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Der Terahertz‐Frequenzbereich umfasst ein technisch wenig erschlossenes Grenzgebiet im elektromagnetischen Spektrum. Es ist aber besonders interessant, weil es im niederenergetischen Bereich viele Eigenfrequenzen, komplexer Quantenphänomene enthält. Dafür stehen neuerdings intensive Terahertz‐Pulse aus spezialisierten Elektronenbeschleunigern zur Verfügung, die Teil 1 dieses Zweiteilers vorgestellt hat. Teil 2 widmet sich der gezielten Suche nach Materialien, die als Grundbausteine für zukünftige Terahertz‐Technologien geeignet sind. Der Schlüssel dazu ist die Beschleunigung quasifreier Ladungsträger durch das starke Terahertz‐Feld, was in bestimmten Materialien besonders nichtlineare Eigenschaften erzeugen kann. Hierfür erweisen sich topologische Isolatoren als sehr komplexe, aber vielversprechende Materialklasse. Sie könnten auch ultraschnelle optoelektronische Bauteile ermöglichen.

Oil-in-water (O/W) microemulsions typically feature a low viscosity and exhibit the ordinary viscosity reduction as a function of temperature. However, for certain applications avoiding or even reverting the temperature trend might be required. This can be conceived by adding thermoresponsive (TR) block copolymers that induce network formation as temperature rises. Accordingly, various ME–polymer mixtures were studied for which three different block copolymer architectures of BAB*, B2AB*, and B(AB*)2 type were employed. Here, “B” represents a permanently hydrophobic, “A” a permanently hydrophilic, and “B*” a TR block. For the TR-block, three different poly(acrylamide)s, namely poly(N-n-propylacrylamide) (pNPAm), poly(N,N-diethylacrylamide) (pDEAm), and poly(N-isopropylacrylamide) (pNiPAm), were used, which all exhibit a lower critical solution temperature (LCST). For a well selected ME concentration, these block copolymers lead to a viscosity enhancement with rising temperature. At a polymer concentration of about 22 g L-1, the most pronounced enhancement was observed for the pNPAm-based systems with factors up to 3, 5, and 8 for BAB*, B2AB*, and B(AB*)2, respectively. This phenomenon is caused by the formation of a transitory network mediated by TR-blocks, as evidenced by the direct correlation between the attraction strength and the viscosity enhancement. For applications requiring a high hydrophobic payload, which is attained via microemulsion droplets, this kind of tailored temperature-dependent viscosity control of surfactant systems should therefore be advantageous.

Fluctuations and stochastic transitions are ubiquitous in nanometre-scale systems, especially in the presence of disorder. However, their direct observation has so far been impeded by a seemingly fundamental, signal-limited compromise between spatial and temporal resolution. Here we develop coherent correlation imaging (CCI) to overcome this dilemma. Our method begins by classifying recorded camera frames in Fourier space. Contrast and spatial resolution emerge by averaging selectively over same-state frames. Temporal resolution down to the acquisition time of a single frame arises independently from an exceptionally low misclassification rate, which we achieve by combining a correlation-based similarity metric1,2 with a modified, iterative hierarchical clustering algorithm3,4. We apply CCI to study previously inaccessible magnetic fluctuations in a highly degenerate magnetic stripe domain state with nanometre-scale resolution. We uncover an intricate network of transitions between more than 30 discrete states. Our spatiotemporal data enable us to reconstruct the pinning energy landscape and to thereby explain the dynamics observed on a microscopic level. CCI massively expands the potential of emerging high-coherence X-ray sources and paves the way for addressing large fundamental questions such as the contribution of pinning5–8 and topology9–12 in phase transitions and the role of spin and charge order fluctuations in high-temperature superconductivity13,14.

In recent years, nonlinear microfluidics in combination with lab-on-a-chip devices has opened a new avenue for chemical and biomedical applications such as droplet formation and cell sorting. In this article, we integrate ideas from active matter into a microfluidic setting, where two fluid layers with identical densities but different viscosities flow through a microfluidic channel. Most importantly, the fluid interface is laden with active particles that act with dipolar forces on the adjacent fluids and thereby generate flows. We perform lattice-Boltzmann simulations and combine them with phase field dynamics of the interface and an advection–diffusion equation for the density of active particles. We show that only contractile force dipoles can destabilize the flat fluid interface. It develops a viscous finger from which droplets break up. For interfaces with non-zero surface tension, a critical value of activity equal to the surface tension is necessary to trigger the instability. Since activity depends on the density of force dipoles, the interface can develop steady deformation. Lastly, we demonstrate how to control droplet formation using switchable activity.

Fouling during membrane emulsification due to biomolecule adsorption is still a drawback for broader applicability and a better holistic understanding is needed. This study aimed to investigate the fouling effect on the membrane and the enzyme being modified due to adsorption. Therefore, a lipase solution with varying concentrations and pH was filtered through a silica-based membrane. The degree of adsorption, membrane properties (microstructure and phase wetting), and enzymatic characteristics (conformation and activity) were evaluated. For insights on the molecular level, molecular dynamic simulations of the conformational changes of lipase caused by adsorption were performed. Regarding the membrane, an increase in lipase concentration increased the adsorption leading to higher fouling and decreased wetting implying a higher hydrophobicity of the membrane. Additionally, SEM showed that the pH of the lipase solution modified the microstructure of the foulant layer. Regarding the impact on the lipase, molecular dynamic simulations revealed an increase in the hydrophobic surface area, a rearrangement of the C-alpha atoms of the protein backbone, and an increase in the radius of gyration. Despite leading to enzyme mass loss, both the secondary structure and the activity showed no significant differences after processing, which might be due to the reversible adsorption.

Physical review / E 107(2), 025206 (2023). doi:10.1103/PhysRevE.107.025206, Published by APS, Woodbury, NY

Funder: Alexander von Humboldt Foundation, Funder: Experienced Researcher Fellowship, Funder: DFG Collaborative, Funder: PAPIIT, Funder: Danish National Research Foundation, Funder: JSPS, Funder: STFC Centre for Instrumentation, Funder: UKSA Centre for Earth, Funder: Leverhulme Trust; doi: http://dx.doi.org/10.13039/501100000275, Funder: NRF, Funder: Royal Society; doi: http://dx.doi.org/10.13039/501100000288, Funder: Australian Government; doi: http://dx.doi.org/10.13039/100015539, Funder: Cancer Research UK; doi: http://dx.doi.org/10.13039/501100000289, Funder: University of Warwick; doi: http://dx.doi.org/10.13039/501100000741, Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

Radical cations of diamondoids are important intermediates in their functionalization reactions in polar solvents. To explore the role of the solvent at the molecular level, we characterize herein microhydrated radical cation clusters of the parent molecule of the diamondoid family, adamantane (C10H16, Ad), by infrared photodissociation (IRPD) spectroscopy of mass-selected [Ad(H2O)n=1–5]+ clusters. IRPD spectra of the cation ground electronic state recorded in the CH/OH stretch and fingerprint ranges reveal the first steps of this fundamental H-substitution reaction at the molecular level. Analysis of size-dependent frequency shifts with dispersion-corrected density functional theory calculations (B3LYP-D3/cc-pVTZ) provides detailed information about the acidity of the proton of Ad+ as a function of the degree of hydration, the structure of the hydration shell, and the strengths of the CH⋯O and OH⋯O hydrogen bonds (H-bonds) of the hydration network. For n = 1, H2O strongly activates the acidic C–H bond of Ad+ by acting as a proton acceptor in a strong CH⋯O ionic H-bond with cation-dipole configuration. For n = 2, the proton is almost equally shared between the adamantyl radical (C10H15, Ady) and the (H2O)2 dimer in a strong C⋯H⋯O ionic H-bond. For n ≥ 3, the proton is completely transferred to the H-bonded hydration network. The threshold for this size-dependent intracluster proton transfer to solvent is consistent with the proton affinities of Ady and (H2O)n and confirmed by collision-induced dissociation experiments. Comparison with other related microhydrated cations reveals that the acidity of the CH proton of Ad+ is in the range of strongly acidic phenol+ but lower than for cationic linear alkanes such as pentane+. Significantly, the presented IRPD spectra of microhydrated Ad+ provide the first spectroscopic molecular-level insight of the chemical reactivity and reaction mechanism of the important class of transient diamondoid radical cations in aqueous solution.

Semiconductor quantum dot molecules are considered as promising candidates for quantum technological applications due to their wide tunability of optical properties and coverage of different energy scales associated with charge and spin physics. While previous works have studied the tunnel-coupling of the different excitonic charge complexes shared by the two quantum dots by conventional optical spectroscopy, we here report on the first demonstration of a coherently controlled inter-dot tunnel-coupling focusing on the quantum coherence of the optically active trion transitions. We employ ultrafast four-wave mixing spectroscopy to resonantly generate a quantum coherence in one trion complex, transfer it to and probe it in another trion configuration. With the help of theoretical modelling on different levels of complexity we give an instructive explanation of the underlying coupling mechanism and dynamical processes.

THz frequencies offer enormous amounts of bandwidth, which could solve the current speed bottleneck for next-generation wireless communications. Recent reports show sub-THz links offering capacities of hundreds of Gbit/s, finally approaching those of state-of-the-art optical transmission channels. Non-etheless, generation, transport, detection and processing of signals in the THz range is far from being a trivial task. Even though the recent evolution of integrated technology is starting to indicate that chip-scale THz technology could gradually close the so-called “THz gap,” much work still needs to be done to enable functional systems, in particular in terms of efficiency. Photonics can be of help, thanks to its extremely low loss and broad bandwidth. Yet, a particularly critical aspect hindering the deployment of THz technology is that state-of-the-art photonics devices generally do not offer sufficient electro-optical bandwidth to process THz signals. Plasmonics, by focusing electromagnetic surface waves at sub-wavelength scales, can play a key role in this quest, as it finally enables the realization of electro-optical devices such as modulators and detectors displaying sufficient compactness and speeds to reach the THz range. This paper overviews recent achievements on plasmonic-based modulators displaying characteristics of speed, efficiency and linearity that enable high-performance access to this much desired frequency range.

We investigate the spontaneous emission noise resilience of the phase-locked operation of two delay-coupled nanolasers. The system is modeled by semi-classical Maxwell–Bloch rate equations with stochastic Langevin-type noise sources. Our results reveal that a polarization dephasing time of two to three times the cavity photon lifetime maximizes the system’s ability to remain phase-locked in the presence of noise-induced perturbations. The Langevin noise term is caused by spontaneous emission processes which change both the intensity auto-correlation properties of the solitary lasers and the coupled system. In an experimental setup, these quantities are measurable and can be directly compared to our numerical data. The strong parameter dependence of the noise tolerance that we find may show possible routes for the design of robust on-chip integrated networks of nanolasers.

The influence of the initial surface roughness of TiAl6V4 samples on the orientation and periodicity of the resulting laser-induced periodic surface structures (LIPSS), as well as the surface wettability and chemistry is reported here. Before LIPSS fabrication, initial sample surface roughness is adjusted by variations of finial polishing steps with polishing grain sizes of 18.3, 8.4, 5, and 0.5 µm. A 3 × 3 irradiation matrix was defined and lasered on all samples by changing the laser power and distance between consecutive laser scans. The resulting structures were characterized by scanning electron microscopy (SEM), atomic force microscopy, Raman spectroscopy, and contact angle measurements. As a further step, three representative generated structures were chosen to explore their bone implant viability by resazurin assays, alkaline phosphatase activity, and direct SEM imaging of the induced cells (MG63) and bacteria (Escherichia coli and Staphylococcus aureus). Results show that initial surface roughness has big influence on the wettability of the resulting surface, as well as inducing small variations on the orientation of the generated LIPSS. Structures generated with a higher integrated fluence have also shown to enhance cell differentiation while reducing bacterial activity, making them a great candidate for improved bone implant compatibility and durability.

Variational quantum machine learning is an extensively studied application of near-term quantum computers. The success of variational quantum learning models crucially depends on finding a suitable parametrization of the model that encodes an inductive bias relevant to the learning task. However, precious little is known about guiding principles for the construction of suitable parametrizations. In this work, we holistically explore when and how symmetries of the learning problem can be exploited to construct quantum learning models with outcomes invariant under the symmetry of the learning task. Building on tools from representation theory, we show how a standard gateset can be transformed into an equivariant gateset that respects the symmetries of the problem at hand through a process of gate symmetrization. We benchmark the proposed methods on two toy problems that feature a non-trivial symmetry and observe a substantial increase in generalization performance. As our tools can also be applied in a straightforward way to other variational problems with symmetric structure, we show how equivariant gatesets can be used in variational quantum eigensolvers., Comment: 25 pages, 15 figures, comments welcome

The luminescence of InxGa1−xN nanowires (NWs) is frequently reported with large red-shifts as compared to the theoretical value expected from the average In content. Both compositional fluctuations and radial built-in fields were considered accountable for this effect, depending on the size, structure, composition, and surrounding medium of the NWs. In the present work, the emission properties of InGaN/GaN NWs grown by plasma-assisted molecular beam epitaxy are investigated in a comprehensive study combining ultraviolet-Raman and photoluminescence spectroscopy (PL) on vertical arrays, polarization-dependent PL on bundles of a few NWs, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and calculations of the band profiles. The roles of inhomogeneous In distribution and radial fields in the context of optical emission properties are addressed. The radial built-in fields are found to be modest, with a maximum surface band bending below 350 meV. On the other hand, variations in the local In content have been observed that give rise to potential fluctuations whose impact on the emission properties is shown to prevail over band-bending effects. Two luminescence bands with large positive and moderate negative polarization ratios of ≈+80% and ≤−60%, respectively, were observed. The red-shift in the luminescence is associated with In-rich inclusions in the NWs due to thermodynamic decomposition during growth. The negative polarization anisotropy is suggested to result from spontaneously formed superlattices in the In-rich regions of the NWs. The NWs show a preferred orthogonal absorption due to the dielectric boundary conditions and highlight the extreme sensitivity of these structures towards light polarization.

In this work, we improve the performance of an optically pumped spintronic terahertz emitter (STE) by a factor of up to 6 in field amplitude through an optimized photonic and thermal environment. Using high-energy pump pulses (energy 5 mJ, fluence >1 mJ/cm2, wavelength 800 nm, duration 80 fs), we routinely generate terahertz pulses with focal peak electric fields above 1.5 MV/cm, fluences of the order of 1 mJ/cm2, and a spectrum covering the range 0.1-11 THz. Remarkably, the field and fluence values are comparable to those obtained from a state-of-the-art terahertz table-top high-field source based on tilted-pulse-front optical rectification in LiNbO3. The optimized STE inherits all attractive features of the standard STE design, for example, ease of use and the straightforward rotation of the terahertz polarization plane, without the typical 75% power loss found in LiNbO3 setups. It, thus, opens up a promising pathway to nonlinear terahertz spectroscopy. Using low-energy laser pulses (2 nJ, 0.2 mJ/cm2, 800 nm, 10 fs), the emitted terahertz pulse has a focal peak electric field of 100 V/cm, which corresponds to a 2-fold improvement, and covers the spectrum 0.3-30 THz., Physical Review Applied, 19 (3), ISSN:2331-7019

We present a microscopic magnetic domain imaging study of single-shot all-optical magnetic toggle switching of a ferrimagnetic Gd26Fe74 film with out-of-plane easy axis of magnetization by X-ray magnetic circular dichroism photoelectron emission microscopy. Individual linearly polarized laser pulses of 800 nm wavelength and 100 fs duration above a certain threshold fluence reverse the sample magnetization, independent of the magnetization direction, the so-called toggle switching. Local deviations from this deterministic behavior close to magnetic domain walls are studied in detail. Reasons for nondeterministic toggle switching are related to extrinsic effects, caused by pulse-to-pulse variations of the exciting laser system, and to intrinsic effects related to the magnetic domain structure of the sample. The latter are, on the one hand, caused by magnetic domain wall elasticity, which leads to a reduction of the domain-wall length at features with sharp tips. These features appear after the optical switching at positions where the line of constant threshold fluence in the Gaussian footprint of the laser pulse comes close to an already existing domain wall. On the other hand, we identify the presence of laser-induced domain-wall motion in the toggle-switching event as a further cause for local deviations from purely deterministic toggle switching.

Recent experiments have reported lower critical solution temperature (LCST) phase behavior of aqueous solutions of proteins induced by multivalent ions, where the solution phase separates upon heating. This phenomenon is linked to complex hydration effects that result in a net entropy gain upon phase separation. To decipher the underlying molecular mechanism, we use all-atom molecular dynamics simulations along with the two-phase thermodynamic method for entropy calculation. Based on simulations of a single BSA protein in various salt solutions (NaCl, CaCl_2, MgCl_2, and YCl_3) at temperatures (T) ranging 283-323 K, we find that the cation-protein binding affinity increases with T, reflecting its thermodynamic driving force to be entropic in origin. We show that in the cation binding process, many tightly bound water molecules from the solvation shells of a cation and the protein are released to the bulk, resulting in entropy gain. To rationalize the LCST behavior, we calculate the {\zeta}-potential that shows charge inversion of the protein for solutions containing multivalent ions. The {\zeta}-potential increases with T. Performing simulations of two BSA proteins, we demonstrate that the protein-protein binding is mediated by multiple cation bridges and involves similar dehydration effects that cause a large entropy gain which more than compensates for rotational and translational entropy losses of the proteins. Thus, the LCST behavior is entropy-driven, but the associated solvation effects are markedly different from hydrophobic hydration. Our findings have direct implications for tuning the phase behavior of biological and soft-matter systems, e.g., protein condensation and crystallization.

We consider analytical, numerical, and experimental approaches developed to describe the mechanical contact between a rigid indenter and an elastic half-space coated with an elastic layer. Numerical simulations of the indentation process were performed using the recently generalized boundary element method (BEM). Analytical approximation of the dependence of contact stiffness on the indenter diameter was used to verify the results of BEM simulations. Adhesive contacts of hard indenters of different shapes with soft rubber layers have been experimentally studied using specially designed laboratory equipment. The comparison of the results from all three implemented methods shows good agreement of the obtained data, thus supporting the generalized BEM simulation technique developed for the JKR limit of very small range of action of adhesive forces. It was shown that the half-space approximation is asymptotical at high ratios of layer thickness h to cylindrical indenter diameter D; however, it is very slowly. Thus, at the ratio h/D = 3.22, the half-space approximation leads to 20% lower contact stiffness compared with that obtained for finite thickness using both an experiment and simulation.

Rhythmic activities that alternate between coherent and incoherent phases are ubiquitous in chemical, ecological, climate, or neural systems. Despite their importance, general mechanisms for their emergence are little understood. In order to fill this gap, we present a framework for describing the emergence of recurrent synchronization in complex networks with adaptive interactions. This phenomenon is manifested at the macroscopic level by temporal episodes of coherent and incoherent dynamics that alternate recurrently. At the same time, the dynamics of the individual nodes do not change qualitatively. We identify asymmetric adaptation rules and temporal separation between the adaptation and the dynamics of individual nodes as key features for the emergence of recurrent synchronization. Our results suggest that asymmetric adaptation might be a fundamental ingredient for recurrent synchronization phenomena as seen in pattern generators, e.g., in neuronal systems.

Dead-end filtration is a facile method to globally align single wall carbon nanotubes (SWCNTs) in large area films with a 2D order parameter, S2D, approaching unity. Uniaxial alignment has been achieved using pristine and hot-embossed membranes but more sophisticated geometries have yet to be investigated. In this work, three different patterns with radial symmetry and an area of 3.8 cm2 are created. Two of these patterns are replicated by the filtered SWCNTs and S2D values of ≈0.85 are obtained. Each of the radially aligned SWCNT films is characterized by scanning cross-polarized microscopy in reflectance and laser imaging in transmittance with linear, radial, and azimuthal polarized light fields. The former is used to define a novel indicator akin to the 2D order parameter using Malu's law, yielding 0.82 for the respective film. The films are then transferred to a flexible printed circuit board and terminal two-probe electrical measurements are conducted to explore the potential of those new alignment geometries.

A small sample size and unbalanced sample distribution are two main problems when data-driven methods are applied for fault diagnosis in practical engineering. Technically, sample generation and data augmentation have proven to be effective methods to solve this problem. The generative adversarial network (GAN) has been widely used in recent years as a representative generative model. Besides the general GAN, many variants have recently been reported to address its inherent problems such as mode collapse and slow convergence. In addition, many new techniques are being proposed to increase the sample generation quality. Therefore, a systematic review of GAN, especially its application in fault diagnosis, is necessary. In this paper, the theory and structure of GAN and variants such as ACGAN, VAEGAN, DCGAN, WGAN, et al. are presented first. Then, the literature on GANs is mainly categorized and analyzed from two aspects: improvements in GAN’s structure and loss function. Specifically, the improvements in the structure are classified into three types: information-based, input-based, and layer-based. Regarding the modification of the loss function, it is sorted into two aspects: metric-based and regularization-based. Afterwards, the evaluation metrics of the generated samples are summarized and compared. Finally, the typical applications of GAN in the bearing fault diagnosis field are listed, and the challenges for further research are also discussed.

Tagging, tracking, or validation of products are often facilitated by inkjet-printed optical information labels. However, this requires thorough substrate pretreatment, ink optimization, and often lacks in printing precision/resolution. Herein, a printing method based on laser-driven deposition of solid polymer ink that allows for printing on various substrates without pretreatment is demonstrated. Since the deposition process has a precision of

Ceramic dielectrics with particularly low levels of dielectric loss and low permittivity are of growing interest toward millimeter-wave applications. Based on composition and structural considerations, lithic kosmochlor is expected to meet these requirements while exhibiting low densification temperatures, allowing its integration also in co-fired circuits. Herein, it is found that the spark plasma sintering of LiCrSi2O6 ceramics facilitates densification at temperatures more than 200 °C lower than conventionally processed materials in only a fraction of the time. A spark plasma sintering duration of 10 min is necessary in order to achieve a controllable process with a repeatable high-performance product material exhibiting a fine-grained microstructure. Characterization millimeter-wave frequencies reveal that LiCrSi2O6 materials produced in this manner exhibit excellent dielectric properties (Qf = 80 700 GHz and εr = 7.5 at 134.24 GHz) following densification at only 950 °C with a relative density of 97.4%. These results represent an unprecedented combination of low dielectric losses and processing temperatures for ceramics processed without the addition of sintering aids. The materials and methods explored here present a promising pathway toward high-performance millimeter-wave and co-firable systems.

The rapid development of microscopic techniques over the past decades enables the establishment of single molecule fluorescence imaging as a powerful tool in biological and biomedical sciences. Single molecule fluorescence imaging allows to study the chemical, physicochemical, and biological properties of target molecules or particles by tracking their molecular position in the biological environment and determining their dynamic behavior. However, the precise determination of particle distribution and diffusivities is often challenging due to high molecule/particle densities, fast diffusion, and photobleaching/blinking of the fluorophore. A novel, accurate, and fast statistical analysis tool, Diffusion Analysis of NAnoscopic Ensembles (DANAE), that solves all these obstacles is introduced. DANAE requires no approximations or any a priori input regarding unknown system-inherent parameters, such as background distributions; a requirement that is vitally important when studying the behavior of molecules/particles in living cells. The superiority of DANAE with various data from simulations is demonstrated. As experimental applications of DANAE, membrane receptor diffusion in its natural membrane environment, and cargo mobility/distribution within nanostructured lipid nanoparticles are presented. Finally, the method is extended to two-color channel fluorescence microscopy.

Funder: Alexander von Humboldt‐Stiftung; Id: http://dx.doi.org/10.13039/100005156, Funder: National Sciences and Engineering Research Council of Canada, Hybrid plasmonic devices involve a nanostructured metal supporting localized surface plasmons to amplify light-matter interaction, and a non-plasmonic material to functionalize charge excitations. Application-relevant epitaxial heterostructures, however, give rise to ballistic ultrafast dynamics that challenge the conventional semiclassical understanding of unidirectional nanometal-to-substrate energy transfer. Epitaxial Au nanoislands are studied on WSe2 with time- and angle-resolved photoemission spectroscopy and femtosecond electron diffraction: this combination of techniques resolves material, energy, and momentum of charge-carriers and phonons excited in the heterostructure. A strong non-linear plasmon-exciton interaction that transfers the energy of sub-bandgap photons very efficiently to the semiconductor is observed, leaving the metal cold until non-radiative exciton recombination heats the nanoparticles on hundreds of femtoseconds timescales. The results resolve a multi-directional energy exchange on timescales shorter than the electronic thermalization of the nanometal. Electron-phonon coupling and diffusive charge-transfer determine the subsequent energy flow. This complex dynamics opens perspectives for optoelectronic and photocatalytic applications, while providing a constraining experimental testbed for state-of-the-art modelling.

During the last decades, the combined efforts of biologists, chemists, and physicists in developing high-field/high-frequency EPR techniques and applying them to functional proteins have demonstrated that this type of magnetic resonance spectroscopy is particularly powerful for characterizing the structure and dynamics of stable and transient states of proteins in action on biologically relevant time scales ranging from nanoseconds to hours. The review article describes how high-field EPR methodology, in conjunction with site-specific isotope and spin-labeling strategies, is capable of providing new insights into fundamental biological processes. Specifically, we discuss the theoretical and instrumental background of continuous-wave and pulse high-field EPR and the multiple-resonance extensions EDNMR, ENDOR, TRIPLE, ESEEM, PELDOR, and RIDME. Some emphasis is placed on a balanced description of both the historical spadework and the achieved performance of advanced EPR at 95 GHz and 360 GHz. This culminates in a coherent treatment of state-of-the-art research of high-field EPR in terms of both instrumentation development and application to representative protein complexes such as cofactor binding sites in photosynthesis.

In this paper, we propose a time-varying coupling function that results in enhanced synchronization in complex networks of oscillators. The stability of synchronization can be analyzed by applying the master stability approach, which considers the largest Lyapunov exponent of the linearized variational equations as a function of the network eigenvalues as the master stability function. Here, it is assumed that the oscillators have diffusive single-variable coupling. All possible single-variable couplings are studied for each time interval, and the one with the smallest local Lyapunov exponent is selected. The obtained coupling function leads to a decrease in the critical coupling parameter, resulting in enhanced synchronization. Moreover, synchronization is achieved faster, and its robustness is increased. For illustration, the optimum coupling function is found for three networks of chaotic Rössler, Chen, and Chua systems, revealing enhanced synchronization.

Femtosecond optical control of magnetic materials shows promise for future ultrafast data storage devices. To date, most studies in this area have relied on quasimonochromatic light in magneto-optical pump-probe experiments, which limited their ability to probe semiconducting and molecule-based materials with structured optical spectra. Here, we demonstrate the possibility of extracting the magneto-optical spectrum of the electrons in the conduction band in the two-dimensional van der Waals ferromagnet Cr2Ge2Te6 (CGT), which is made possible due to broadband probing in the visible spectrum. The magneto-optical signal is a sum of contributions from electrons in the conduction and valence bands, which are of opposite sign for CGT. Depending on the probe wavelength used, this difference could lead to an erroneous interpretation that the magnetization direction is reversed after excitation, which has important consequences for understanding spin toggle switching phenomena.

For the study of symmetry-breaking phenomena in neuronal networks, simplified versions of the FitzHugh-Nagumo model are widely used. In this paper, these phenomena are investigated in a network of FitzHugh-Nagumo oscillators taken in the form of the original model and it is found that it exhibits diverse partial synchronization patterns that are unobserved in the networks with simplified models. Apart from the classical chimera, we report a new type of chimera pattern whose incoherent clusters are characterized by spatial random swings among a few fixed periodic attractors. Another peculiar hybrid state is found that combines the features of this chimera state and a solitary state such that the main coherent cluster is interspersed with some nodes with identical solitary dynamics. In addition, oscillation death including chimera death emerges in this network. A reduced model of the network is derived to study oscillation death, which helps explaining the transition from spatial chaos to oscillation death via the chimera state with a solitary state. This study deepens our understanding of chimera patterns in neuronal networks.

The combination of high spatial and temporal resolution is still a limiting factor in the field of surface science. Only very recently, a novel experimental approach has been presented that allows versatile access to this regime by combining ultrafast Terahertz (THz) pulses with the extraordinary spatial resolution of scanning tunneling microscopy (STM): The so-called THz-STM. In this device, the THz pulses act as ultrafast transient bias voltage and hence allow to unravel the ultrafast physics of highly localized electronic states via pump-probe experiments. In this thesis, we describe the process of establishing this novel technique in our group. We firstly discuss the new configuration of the designated lab, the design and alignment of our THz-source as well as its characterization using electro-optic sampling. Subsequently we describe the modifications performed on the preexisting STM to facilitate the coupling of THz radiation. The THz-STM was thoroughly tested in different scenarios showcasing its capabilities. We initially present data originating from optical-pump, THz-probe measurements based on photoelectron emission, confirming the successful coupling of ultrashort THz pulses into the STM. Subsequent measurements using field emission resonances show the stability of our system under cryo conditions and using junctions at tunneling distances. Experiments involving Kondo resonances of point defects in MoS2 prove the sensitivity of our THz-STM when used with small nonlinearities and are used to perform exemplary spatially resolved measurements. Finally we present preliminary time-resolved data as part of an outlook.

Microswimmer suspensions are a paradigmatic example of active matter, a term that describes living or artificial systems consisting of actively moving constituents. The non-equilibrium nature of these self-propelled particles leads to diverse collective behavior and pattern formation. In this thesis, we investigate the flow patterns emerging in microswimmer suspensions such as swimming bacteria. To this end, we rely on a continuum-theoretical description in terms of order parameter fields that we derive on the basis of a generic microscopic model for the swimmers. Our derivation incorporates near-field alignment interactions and far-field hydrodynamic interactions that are mediated by the solvent flow. The Stokes equation governing the solvent flow dynamics has to be supplemented by an ansatz for the active stress resulting from the self-propulsion mechanism. Here, we employ an expansion that leads to higher order gradient terms in the final partial differential equation for the polar order parameter. For weak coupling between solvent flow and polar order parameter, we can further show that our coarse-grained description reduces to a minimal model that was introduced in the context of mesoscale turbulence, a highly dynamic spatiotemporal flow state observed in bacterial suspensions. This reduced model considers solely the dynamics of an effective microswimmer velocity field and also relies on the interplay of higher order gradient terms to reproduce one of the key features of mesoscale turbulence: the selection of a characteristic length scale or vortex size. We focus our efforts on the minimal model to explore the emerging patterns including regular vortex lattices and the turbulent state. In particular, we uncover intriguing transport properties such as a parameter region of optimal turbulent diffusion mediated by the complex interplay of different time scales in the flow. Further, we propose and investigate two methods of controlling the emerging structures. First, we employ an external field that reorients the swimmers in a certain direction. This rotational constraint leads to highly anisotropic, stripe-like structures and can even suppress the pattern formation altogether. Second, we show that strategically placed obstacles can reorganize the microswimmer flow field into a variety of vortex structures with different properties. In addition to the stabilization of symmetric patterns such as square and triangular vortex lattices, we also show how a Kagome arrangement of obstacles can induce a chiral structure characterized by a net rotational flow as a result of the spontaneous symmetry breaking. We further uncover an intriguing analogy to an equilibrium phase transition. Remarkably, the emergence of global ordering in the square vortex lattice can be mapped to a spin system with Ising symmetry and antiferromagnetic coupling., Suspensionen von Mikroschwimmern sind ein Musterbeispiel für aktive Materie. In diesen Nichtgleichgewichtssystemen aus sich selbst antreibenden Einheiten beobachtet man vielfältiges kollektives Verhalten und Strukturbildung. In dieser Arbeit untersuchen wir die Strömungsmuster, die in Suspensionen von Mikroschwimmern wie schwimmenden Bakterien entstehen. Hierfür nutzen wir eine kontinuumstheoretische Beschreibung mittels Ordnungsparametern, die wir auf Basis eines generischen mikroskopischen Modells herleiten. Wir berücksichtigen sowohl kurzreichweitige Ausrichtungswechselwirkungen als auch länger reichende hydrodynamische Wechselwirkungen. Zentral ist hierbei der Ansatz für den aktiven Spannungstensor als Folge der Schwimmbewegungen, welcher zu Gradiententermen höherer Ordnung in der Gleichung für den polaren Ordnungsparameter führt. Bei schwacher Kopplung zwischen polarer Ordnung und Lösungsmittelströmung lassen sich die hergeleiteten Gleichungen reduzieren auf ein bekanntes Mimimalmodell zur Beschreibung von Mesoskalen-Turbulenz, ein hochgradig dynamischer Strömungszustand, der in Bakteriensuspensionen beobachtet wurde. Im reduzierten Modell wird hierbei nur die Dynamik eines effektiven Mikroschwimmergeschwindigkeitsfeldes betrachtet. Gradiententerme höherer Ordnung spielen dabei eine zentrale Rolle und führen zu einem der Hauptmerkmale von Mesoskalen-Turbulenz, dem Herausbilden einer charakteristischen Längenskala bzw. Wirbelgröße. Der Fokus dieser Arbeit liegt auf den Strukturen, die im Minimalmodell entstehen, wozu neben dem turbulenten Zustand auch regelmäßige Wirbelgitter zählen. Mit Hinblick auf mögliche Anwendungen sind insbesondere Transporteigenschaften relevant. Hierbei finden wir einen Parameterbereich mit optimaler turbulenter Diffusion als Folge des Zusammenspiels verschiedener Zeitskalen in der Strömung. Zur Kontrolle der Strukturbildung beschäftigen wir uns mit zwei verschiedenen Methoden. Die erste beinhaltet ein externes Feld, welches den Schwimmern eine bevorzugte Bewegungsrichtung vorgibt. Diese Einschränkung des Rotationsfreiheitsgrades führt zu anisotropen, streifenartigen Mustern und kann die Strukturbildung sogar komplett unterdrücken. Zweitens zeigen wir, wie strategisch platzierte Hindernisse die Mikroschwimmerströmung umleiten und so Wirbelstrukturen mit unterschiedlichen Eigenschaften erzeugen können. Zusätzlich zu symmetrischen Mustern wie quadratischen und triangulären Wirbelgittern stabilisieren wir ein chirales Muster, welches eine Rotationsströmung induziert, indem wir die Hindernisse in einem Kagome-Gitter anordnen. Des Weiteren zeigen wir eine faszinierende Analogie zu Gleichgewichtsphasenübergängen auf, indem wir das Entstehen globaler Ordnung im quadratischen Wirbelgitter auf ein Spin-System mit Ising-Symmetrie und antiferromagnetischer Kopplung abbilden.

Lithium fluoride (LiF) crystals and thin films have been successfully investigated as X-ray imaging detectors based on optical reading of visible photoluminescence emitted by stable radiation-induced F2 and F3 + colour centres. In this work, the visible photoluminescence response of optically-transparent LiF film detectors of three different thicknesses, grown by thermal evaporation on Si(100) substrates and irradiated with monochromatic 7 keV X-rays at several doses in the range between 13 and 4.5× 103 Gy, was carefully investigated by fluorescence optical microscopy. For all the film thicknesses, the photoluminescence response linearly depends on the irradiation dose in the investigated dose range. The lowest detected dose, delivered to the thinnest LiF film, only 0.5 μm thick, is estimated 13 Gy. Edge-enhancement imaging experiments, conducted by irradiating LiF film detectors at the same energy placing an Au mesh in front of them at a distance of 15 mm, allowed estimating a spatial resolution of (0.38 ± 0.05) μm, which is comparable to the microscope one. This very high spatial resolution in LiF film radiation detectors based on colour centres photoluminescence is combined with the availability of a wide field of view on large areas.

Stellarators are attractive candidates for commercial fusion power plants: they inherently operate in steady-state and, unlike tokamaks, do not require a plasma current to obtain magnetic confinement, which can lead to current-driven disruptions. The concept of stellarators was first proposed over 70 years ago and now gains renewed interest as a candidate for commercial fusion power plants, mainly caused by the successful operation of the large stellarator experiment ‘Wendelstein 7-X’ [1]. Advances in stellarator optimisation now make it possible to suggest configurations that meet nearly all necessary criteria for a fusion reactor from a physics point of view. In addition, it is possible to find stellarator configurations that are more compact, and thus more economical, and have less turbulent activity than previously suggested configurations. Systems code studies are holistic tools, which are crucial to extrapolate a stellarator to a consistent fusion reactor design point, which matches with physics, engineering and economical constraints. By modelling all relevant properties and boundary conditions, using reduced and computationally fast models, it is possible to quantify these design points and also learn about sensitivities, correlations and relevant trade-offs. However, so far, systems-code studies have mainly been employed for the tokamak concept only, as part of the European tokamak DEMO activity. Because stellarators are not bound to toroidal symmetry, as tokamaks are, they allow for drastically different configurations, especially with respect to the plasma shape and the non-planar coil geometry. To model this vast design space, it is required to develop systems code models, that allow to model a large space of different stellarator configurations within a single code framework. A systems code for such general stellarators did not exist before this work. In this work, a new set of stellarator systems code models is developed and implemented in the European fusion reactor systems code ‘Process’. With these modifications, it is possible to model generic modular stellarators, requiring only the plasma shape and the central coil filaments of the non-planar coils as inputs. This work bases on previous contributions [2], which implemented models for one specific stellarator configuration, namely the Helias 5 stellarator configuration, based on parameters of a respective engineering study [3]. The dependency to such an engineering study was resolved in this work, and a set of models was developed and implemented that are applicable to generic modular stellarators. The new stellarator version of Process is used then to for the first time find a cost-optimised design point of a Helias 5 stellarator, using differently aggressive technology assumptions, find a set of design points for a high field, intermediate-step, prototype stellarator, given uncertainties on certain input parameters, evaluate the relative importance of common targets in stellarator optimization quantitatively in terms of their economical relevance, and lastly demonstrate the usage of Process as a penalty function for different stellarator coil-sets and its possible application for stellarator coil optimisation. The thesis contributes to the area of stellarator systems code studies for fusion power plants and develops models that take the fact into account that there is a growing number of new stellarator configurations available, made possible by recent optimisation advancements., Stellaratoren sind attraktive Kandidaten für kommerzielle Fusionsreaktoren: Im Gegensatz zu Tokamaks operieren Stellaratoren intrinsisch kontinuierlich, und sind, um magnetischen Einschluss zu erreichen, nicht auf einen internen Plasmastrom angewiesen, der zu stromgetriebenen Disruptionen führen kann. Das stellarator Konzept wurde bereits vor fast 70 Jahre vorgeschlagen und erlebt vor allem durch die erfolgreiche Inbetriebnahme des Stellarator-Reaktor-Prototypen ‘Wendelstein 7-X’ [1] erneute Aufmerksamkeit als Kandidat für einen kommerziellen Fusionsreaktor. Weitere Fortschritte in den letzten Jahren in der Optimierung von Stellaratoren ermöglichen es nun, Stellarator-Konfigurationen vorzuschlagen, die fast alle für einen Reaktor notwendigen Kriterien erfüllen. Zudem ist es nun möglich, kompakte Stellaratoren zu finden und Konfigurationen mit reduzierter Turbulenz, die momentan maßgeblich den Einschluss in Wendelstein 7-X limitiert. System-Code-Studien spielen für die Extrapolation zu einem Reaktor und eine entsprechende Stellarator-Reaktoroptimierung eine wichtige Rolle: Durch das vollständige Modellieren aller relevanten Eigenschaften und Randbedinungen mithilfe reduzierter Modelle in einem integrierten Computer-Code, wird es ermöglicht, Erkenntnisse über Reaktor Design Punkte, Sensitivitäten, Korrelationen, relevante Kompromisse und über ökonomische Eigenschaften zu erlangen. System-Codes haben den Vorteil, dass sie physikalische, technologische und ökonomische Aspekte modellieren und somit Design Punkte finden können, die mit allen drei Aspekten übereinstimmen. Solche System-Code-Studien werden momentan vor allem für die Reaktor Extrapolation von Tokamaks verwendet, zum Beispiel als Teil der europäischen DEMO Aktivität, die das Konzept eines Tokamak-Reaktors verfolgt. Da Stellaratoren durch ihre niedrigere axiale Symmetrie weitaus verschiedenere Designlösungen ermöglichen, vor allem im Bezug auf Plasmaform und auf Spulengeometrie, ist es vonnöten, System-Code-Modelle zu entwickeln, die eine große Anzahl möglichst generischer Stellarator Konfigurationen modellieren können. Solch ein Satz von Modellen existierte bis zum Zeitpunkt der vorliegenden Arbeit nicht. In dieser Arbeit wird eine Reihe von System-Code-Modellen entwickelt und in den europäischen Fusions-Reaktor System-Code „Process“ implementiert, der es anschließend ermöglicht, allgemeine, modulare Stellaratoren zu modellieren, auf Basis der letzten Flussfläche des Stellarator-Plasmas und auf Basis des entsprechenden Spulensets, das in der Regel durch nichtplanare zentrale Spulenfilamente beschrieben wird. Diese Arbeit knüpft an vorige Arbeiten an [2], die einen reduzierten Satz an Modellen für eine bestimmte Stellarator Konfiguration, die Helias 5 Konfiguration, auf Basis einer separaten Studie [3] implementiert hatten. Die Abhängigkeit von solch einer Studie wurde in dieser Arbeit gelöst, sowie ein Satz von Modellen entwickelt und implementiert, die auf generische Stellaratoren anwendbar ist. Anschließend an die Beschreibung der in Process implementierten Modelle wird Process, nun für generische modulare Stellaratoren geignet, eingesetzt um zum ersten Mal einen Kosten-optimierten Designpunkt eines optimierten Helias 5 stellarators vorzuschlagen mit verschieden aggressiven Technologie-Annahmen, einen Satz an Designpunkten eines Hoch-Feld Prototyp-Stellarators vorzuschlagen, als Zwischenschritt zu einem Reaktor, gegeben einiger Unsicherheiten auf relevante Anfangsparameter, die relative Wichtigkeit von Optimierungs-Zielen in der Stellarator Optimierung quantitativ zu evaluieren, und zuletzt den Einsatz von Process als Kostenfunktion für verschiedene Stellarator Spulensätze zu demonstrieren und dessen möglichen Einsatz für Stellarator Spulen Optimierung zu zeigen. Die vorliegende Arbeit trägt zu der System-Studien Modellierung von Stellaratoren als Fusionskraftwerke bei. Die Art der implementierten Modelle und die Resultate in dieser Arbeit berücksichtigen den Trend einer stark wachsenden Anzahl an verfügbaren Stellarator-Konfigurationen, die durch Fortschritte in der Stellarator-Optimierung ermöglicht werden.

The molecular interactions of numerous real fluids, like argon, nitrogen, or carbon dioxide, are adequately described by the two-center Lennard-Jones plus quadrupole potential. Applying this model class in molecular dynamics simulations, evaporation is investigated systematically. The influence of the molecular anisotropy and quadrupole as well as the boundary conditions, i.e., bulk liquid temperature and evaporation magnitude, is reported. A method for specifying the evaporation magnitude in terms of hydrodynamic velocity is further developed for that purpose. Analyses show that the largest molar flux and energy flux occur for spherical molecules and that anisotropy and quadrupole influence several quantities. Depending on the bulk liquid temperature, the quadrupole predominantly affects the interface temperature, while the anisotropy of the molecule significantly influences the interface temperature as well as both molar and energy fluxes. In addition, the preferred average orientation of the molecules in the interface region is investigated. The evaporation coefficient is determined, and thermodynamic states traversed during the evaporation process are discussed.

Many quantum information protocols require the implementation of random unitaries. Because it takes exponential resources to produce Haar-random unitaries drawn from the full $n$-qubit group, one often resorts to $t$-designs. Unitary $t$-designs mimic the Haar-measure up to $t$-th moments. It is known that Clifford operations can implement at most $3$-designs. In this work, we quantify the non-Clifford resources required to break this barrier. We find that it suffices to inject $O(t^{4}\log^{2}(t)\log(1/\varepsilon))$ many non-Clifford gates into a polynomial-depth random Clifford circuit to obtain an $\varepsilon$-approximate $t$-design. Strikingly, the number of non-Clifford gates required is independent of the system size -- asymptotically, the density of non-Clifford gates is allowed to tend to zero. We also derive novel bounds on the convergence time of random Clifford circuits to the $t$-th moment of the uniform distribution on the Clifford group. Our proofs exploit a recently developed variant of Schur-Weyl duality for the Clifford group, as well as bounds on restricted spectral gaps of averaging operators., v3: version published in Communications in Mathematical Physics, title changed; v2: improved presentation, added consequences of the main result and fixed typos; 46 pages, 1 figure

We study numerically effects of time delay in networks of delay-coupled excitable FitzHugh–Nagumo systems with dissipation. Generation of periodic self-sustained oscillations and its threshold are analyzed depending on the dissipation of a single neuron, the delay time, and random initial conditions. The peculiarities of spatiotemporal dynamics of time-delayed bidirectional ring-structured FitzHugh–Nagumo neuronal systems are investigated in cases of local and nonlocal coupling topology between the nodes, and a first-order nonequilibrium phase transition to synchrony is established. It is shown that the emergence of an oscillatory activity in delay-coupled FitzHugh–Nagumo neurons is observed for smaller values of the coupling strength as the dissipation parameter decreases. This can provide the possibility of controlling the spatiotemporal behavior of the considered neuronal networks. The observed effects are quantified by plotting distributions of the maximal Lyapunov exponent and the global order parameter in terms of delay and coupling strength.

Flexible characterization techniques that identify and quantify experimental imperfections under realistic assumptions are crucial for the development of quantum computers. Gate set tomography is a characterization approach that simultaneously and self-consistently extracts a tomographic description of the implementation of an entire set of quantum gates, as well as the initial state and measurement, from experimental data. Obtaining such a detailed picture of the experimental implementation is associated with high requirements on the number of sequences and their design, making gate set tomography a challenging task even for only two qubits. In this work, we show that low-rank approximations of gate sets can be obtained from significantly fewer gate sequences and that it is sufficient to draw them randomly. Such tomographic information is needed for the crucial task of dealing with coherent noise. To this end, we formulate the data processing problem of gate set tomography as a rank-constrained tensor completion problem. We provide an algorithm to solve this problem while respecting the usual positivity and normalization constraints of quantum mechanics by using second-order geometrical optimization methods on the complex Stiefel manifold. Besides the reduction in sequences, we demonstrate numerically that the algorithm does not rely on structured gate sets or an elaborate circuit design to robustly perform gate set tomography. Therefore, it is more flexible than traditional approaches. We also demonstrate how coherent errors in shadow estimation protocols can be mitigated using estimates from gate set tomography., Comment: 14+12 pages, several figures and diagrams; v2: An error in our interface to pyGSTi has been corrected and Sections IV.A and IV.B have been reworked; v3: Added a new section on noise mitigation for shadow estimation with compressive GST, a corresponding appendix, an improved runtime table and various clarifications

Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modeling, two excitation processes of spin dynamics in NiO: an off-resonant instantaneous optical spin torque in (111) oriented films and a strain-wave-induced THz torque induced by ultrafast Pt excitation in (001) oriented films. Both phenomena lead to the emission of a THz signal through the inverse spin Hall effect in the adjacent heavy metal layer. We unravel the characteristic timescales of the two excitation processes found to be 300 fs, respectively, and thus open new routes towards the development of fast opto-spintronic devices based on antiferromagnetic materials.

We show that two seemingly unrelated problems - the trapping of an atom in an optical superlattice (OSL) and the libration of a planar rigid rotor in combined electric and optical fields - have isomorphic Hamiltonians. Formed by the interference of optical lattices whose spatial periods differ by a factor of two, OSL gives rise to a periodic potential that acts on atomic translation via the AC Stark effect. The latter system, also known as the generalized planar pendulum (GPP), is realized by subjecting a planar rigid rotor to combined orienting and aligning interactions due to the coupling of the rotor's permanent and induced electric dipole moments with the combined fields. The mapping makes it possible to establish correspondence between concepts developed for the two eigenproblems individually, such as localization on the one hand and orientation/alignment on the other. Moreover, since the GPP problem is conditionally quasi-exactly solvable (C-QES), so is atomic trapping in an OSL. We make use of both the correspondence and the quasi-exact solvability to treat ultracold atoms in an optical superlattice as a semifinite-gap system. The band structure of this system follows from the eigenenergies and their genuine and avoided crossings obtained previously for the GPP as analytic solutions of the Whittaker-Hill equation. These solutions characterize both the squeezing and the tunneling of atoms trapped in an optical superlattice and pave the way to unraveling their dynamics in analytic form., 25 pages, 12 figures, 2 tables, Submitted to the New Journal of Physics

Single-crystalline antiferromagnetic artificially layered [Ni/Mn] films of different thicknesses, covered by ferromagnetic Co layers, are deposited on Cu3Au(001).Their structural and magnetic properties are characterized by low-energy electron diffraction (LEED) and magneto-optical Kerr effect, respectively, and compared with disordered NixMn100-x alloy films with the same Ni/Mn ratio and the same film thickness. LEED intensity-versus-energy curves show that the perpendicular inter-atomic lattice distance is decreased in the artificially layered [Ni/Mn] samples incomparison to the disordered NixMn100-x alloy films.At the same time, the artificially layered [Ni/Mn] films exhibit higher coercivity and exchange bias of the adjacent Co layer compared to those of NixMn100-x/Co. This is discussed as a consequence of the different interatomic lattice distance, presumably caused by an ordered buckling in the artificially layered [Ni/Mn] samples, leading to a stronger interlayer exchange coupling.

The application of anti-corrosion coated, high-strength steels in the automotive industry has increased in recent years. In combination with various zinc-based surface coatings, liquid metal embrittlement cracking can be observed in some of these materials. A high-quality, crack-free spot-welded joint is essential to realize the lightweight potential of the materials. In this work, the LME susceptibility of different coatings, which will be determined by the crack length and the occurrence rate, will be investigated using a welding under external load setup. The uncoated specimens did not show any LME. EG, GI and GA showed significantly less LME than ZM coatings. The latter coatings showed much larger crack lengths than the EG, GI and GA coatings. Furthermore, two mechanisms regarding the LME occurrence rate were observed: the occurrence of LME in zinc–magnesium coatings was theorized to be driven by the material properties of the coatings, whereas the occurrence of LME at EG, GI and GA samples was forced mainly by the application of the external tensile load. In the experimental setup of this work, the materials were exposed to unusually high mechanical loads (up to 80% of their yield strength) to evoke LME cracks.

In this work we study the effects of high-temperature annealing on epitaxial AlN films, grown on (0001) sapphire substrates by metal-organic vapor phase epitaxy (MOVPE) and RF-sputtering. Combining transmission electron microscopy (TEM) techniques with secondary ion mass spectrometry (SIMS), we study the microstructural changes of the layers following thermal annealing at temperatures in the 1500-1740°C range. The investigations reveal the following results: (i) Oxygen diffuses from the sapphire to the AlN layer during annealing. Two diffusion mechanisms are active: a fast pipe-diffusion through the high density of threading dislocations (initially ~1010 cm-2), and a slower bulk diffusion radially from the dislocations. This establishes diffusion cylinders in the material around the dislocations, containing oxygen at the solubility limit for the given temperature. (ii) Vacancy complexes (VAl–2ON+) form during the annealing as compensating defects to the electrically active oxygen impurities (ON-). These vacancy complexes, forming in the vicinity of threading dislocations, drive the climb-motion of the dislocations, which drives the crystal recovery observed upon annealing. (iii) AlN layers grown by RF-sputtering exhibit a lower dislocation density than MOVPE-grown ones after annealing. We assign this to the presence of densely distributed nanopipes in the as-grown film. The nanopipes upon annealing transform through necking into faceted voids, which undergo Ostwald ripening, thereby injecting vacancies into the films. The total density of these vacancies exceeds by far the equilibrium concentration that is present in the volume due to oxygen doping at the annealing temperature, and efficiently promote the crystal recovery. (iv) Sputter-grown AlN layers exhibit a columnar structure due to the formation of basal stacking faults (BSF) that fold into prismatic stacking faults (PSF). These faulted domains shrink and disappear upon annealing, via a climb-motion of the PSFs, promoted by the large concentration of vacancies and driven by the reduction in interfacial energy., In dieser Arbeit untersuchen wir die Auswirkungen des Hochtemperatur-Ausheilens auf epitaktische AlN-Schichten, die durch metallorganische Gasphasenepitaxie (MOVPE) und RF-Sputtern auf (0001) Saphirsubstraten abgeschieden wurden. Mittels Transmissionselektronenmikroskopie (TEM) und Sekundärionen-Massenspektrometrie (SIMS) untersuchen wir die mikrostrukturellen Veränderungen der Schichten nach dem thermischen Ausheilen bei Temperaturen im Bereich von 1500-1740°C. Die Untersuchungen zeigen die folgenden Ergebnisse: (i) Sauerstoff diffundiert während des Ausheilens vom Saphirsubstrat in die AlN-Schicht. Dabei sind zwei Diffusionsmechanismen aktiv: eine schnelle Pipediffusion durch die hohe Dichte von Fadenversetzungen (anfänglich ~1010 cm-2) und eine langsamere Volumendiffusion radial von den Versetzungen weg. Dadurch bilden sich im Material um die Versetzungen herum Diffusionszylinder, in denen die Sauerstoff die Sättigung bei der gegebenen Ausheilungstemperatur erreicht. (ii) Während des Ausheilens bilden sich Leerstellenkomplexe (VAl-2ON+) die die Sauerstoffverunreinigungen (ON-) elektrisch kompensieren. Diese Leerstellenkomplexe, die sich in der Nähe von Fadenversetzungen bilden, treiben die Kletterbewegung der Versetzungen, die für die beim Ausheilen beobachtete Kristallerholung verantwortlich ist. (iii) AlN-Schichten, die durch RF-Sputtern gezüchtet wurden, erreichen beim Ausheilen eine geringere Versetzungsdichte als MOVPE-gezüchtete Schichten. Wir führen dies auf Nanoröhren zurück, die in den wie-gewachsenen Schichten hoher Dichte auftreten. Diese Nanoröhren transformieren sich während des Auslheilens durch Einschnürung in facettierte Poren die dann der Ostwald-Reifung unterliegen. Dadurch werden Leerstellen in die Schicht injiziert. Die totale Konzentration dieser Leerstellen überschreitet bei weitem die Gleichgewichtskonzentration die durch Sauerstoffdotierung bei den gegebenen Ausheilungstemperaturen erreichbar ist und fördert so effektiv die Kristallerholung. (iv) Durch Sputtern gewachsene AlN-Schichten weisen eine säulenartige Struktur auf, die auf die Bildung von basalen Stapelfehlern (BSF) zurückzuführen ist, die sich zu prismatischen Stapelfehlern (PSF) falten. Diese gestörten Domänen schrumpfen und verschwinden beim Ausheilen durch eine Kletterbewegung der PSFs, die durch die hohe Konzentration von Leerstellen und die Verringerung der Grenzflächenenergie getrieben wird.

Current flow in electronic devices can be asymmetric with bias direction, a phenomenon underlying the utility of diodes1 and known as non-reciprocal charge transport2. The promise of dissipationless electronics has recently stimulated the quest for superconducting diodes, and non-reciprocal superconducting devices have been realized in various non-centrosymmetric systems3–10. Here we investigate the ultimate limits of miniaturization by creating atomic-scale Pb–Pb Josephson junctions in a scanning tunnelling microscope. Pristine junctions stabilized by a single Pb atom exhibit hysteretic behaviour, confirming the high quality of the junctions, but no asymmetry between the bias directions. Non-reciprocal supercurrents emerge when inserting a single magnetic atom into the junction, with the preferred direction depending on the atomic species. Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle currents flowing by means of electron–hole asymmetric Yu–Shiba–Rusinov states inside the superconducting energy gap and identify a new mechanism for diode behaviour in Josephson junctions. Our results open new avenues for creating atomic-scale Josephson diodes and tuning their properties through single-atom manipulation.

The one-sided Möbius strip with its characteristic 180° twist in the loop has inspired philosophers, artists and scientists since hundreds of years and continues to do so. On the molecular level, only in the last 15 years have some groups succeeded in synthesizing new expanded porphyrin compounds large enough to adopt Möbius-strip topology and Möbius aromaticity, the first being Lechosław Latos-Grażyński and collaborators in Wroclaw (2007) and Atsuhiro Osuka and collaborators in Kyoto (2008). We report on new studies of expanded porphyrins with either Möbius topology or Hückel topology that were synthesized in these laboratories. In this minireview, we focus on recent continuous-wave and time-resolved EPR, ENDOR and DFT MO studies on open-shell states of di-p-benzi[28]hexaphyrin(1.1.1.1.1.1), specifically, on the ground-state radical cation doublet state (total electron spin S = 1/2) and the first excited triplet state (S = 1). The review is largely based on the results and discussions of two previous publications: Möbius et al. (Appl Magn Reson 47:757–780, 2016) and Ema et al. (J Phys Chem Lett 9:2685–2690, 2018). In the open-shell systems, besides the electron-nuclear hyperfine couplings also the zero-field interaction tensor turned out to be a viable sensor for electronic structure changes between Möbius and Hückel topologies. In the Outlook section, we address the cyclotides, a new class of natural circular mini-proteins, usually less than 100 amino acids long. They are distinguished by exceptional chemical and biological stability. This is due to topological constraints imposed by threefoil knot and Möbius-strip formation. As a result, their physical qualities are “topologically protected”. This makes them highly interesting for medical or agricultural applications, for example as novel active ingredients against autoimmune diseases, viral infections, or as agents against insect damage to crops.

With the emerging availability of intense attosecond pulses and pulse trains in the X-ray and extreme ultraviolet (XUV) regime at free-electron lasers, and high harmonic generation sources, fast electronic dynamics in single nanostructures are becoming accessible for imaging techniques. This work addresses the detection of ultrafast electronic dynamics down to the attosecond domain in single nanoparticles using coherent light scattering. In particular, scattering images of helium nanodroplets, which serve as a simple model system, are produced using XUV light. In order to provide the necessary particularly high intensities, an intense XUV light source based on high harmonic generation has been developed in a collaboration of several research groups at the Max Born Institute. Besides the optimization of the generation process itself, the geometry of the associated beamline significantly determines the achievable intensities. To use the maximum intensities also for imaging helium droplets, a new experimental setup was designed. It includes focusing optics specially developed for this experiment and several tools for characterizing the pulses interacting with the helium droplets. Both the development of the intensity-optimized XUV light source and the experimental setup have made it possible to detect a change in the scattering response of helium droplets induced by a near-infrared (NIR) laser pulse on the femto- to even attosecond time scale. In agreement with a previous measurement, a reduced scattering signal was now routinely observed during simultaneous illumination of the droplets with NIR and XUV pulses. Moreover, a change in the amount of scattered light during simultaneous illumination was observed when the time delay of the two pulses was varied in the attosecond range. In fact, an oscillation of the scattered signal with a period of about half an NIR laser pulse cycle was measured and reproduced several times. By modeling the experiment through the dipole response of a single electron in a helium atom, the observed change can be attributed to phenomena known from atomic physics, namely the AC Stark shift and light-induced states. In particular, the observed oscillation per NIR half cycle is attributed to quantum path interference occurring in light-induced states. The experiment in this work is one of the first to detect attosecond electron dynamics in individual nanoparticles by coherent light scattering. This opens up new possibilities for the temporally and spatially resolved study of electronic processes in condensed matter on the nanoscale., Mit der zunehmenden Verfügbarkeit intensiver Attosekundenpulse und -pulszüge im Röntgen- und extrem ultraviolettem (XUV) Bereich an Freie-Elektronen-Laser und mit Hilfe von der Erzeugung hoher Harmonischer wird die schnelle elektronische Dynamik in einzelnen Nanostrukturen für bildgebende Verfahren zugänglich. Diese Arbeit befasst sich mit dem Nachweis ultraschneller elektronischer Dynamiken bis in den Attosekundenbereich in einzelnen Nanopartikeln mittels kohärenter Lichtstreuung. Im speziellen werden Streubilder von Heliumnanotröpfchen, welche als einfaches Modellsystem dienen, mit XUV Licht erzeugt. Damit die notwendigen besonders hohen Intensitäten zur Verfügung stehen, wurde in einer Zusammenarbeit mehrerer Forschungsgruppen am Max-Born-Institut eine intensive XUV-Lichtquelle auf Basis von der Erzeugung von hohen Harmonischen entwickelt. Neben der Optimierung des Erzeugungs-Prozesses selbst, bestimmt die Geometrie der zugehörigen Strahlführung maßgeblich die erreichbaren Intensitäten. Um auch bei der Abbildung von Heliumtröpfchen von maximalen Intensitäten profitieren zu können, wurde zudem ein neuer Versuchsaufbau konzipiert. Dieser umfasst unter anderem eine speziell für dieses Experiment entwickelte Fokussieroptik und mehrere Werkzeuge zur Charakterisierung der mit den Heliumtröpfchen wechselwirkenden Pulse. Sowohl die Entwicklung der intensitätsoptimierten XUV-Lichtquelle als auch des Versuchsaufbaus haben es ermöglicht, eine durch einen nahinfraroten (NIR) Laserpuls induzierte Änderung der Streureaktion von Heliumtröpfchen auf der Femto- bis sogar Attosekunden-Zeitskala nachzuweisen. Es konnte in Übereinstimmung mit einer früheren Messung nun routinemäßig ein reduziertes Streusignal bei gleichzeitiger Ausleuchtung der Tröpfchen mit NIR- und XUV-Pulsen beobachtet werden. Darüber hinaus wurde insbesondere eine Änderung der Menge an gestreutem Licht während der gleichzeitigen Ausleuchtung auch dann beobachtet, wenn die Zeitverzögerung der beiden Pulse im Attosekundenbereich variiert wurde. Tatsächlich wurde eine Oszillation des Streusignals mit einer Periode von etwa einem halben NIR-Laserpulszyklus gemessen und mehrfach reproduziert. Durch die Modellierung des Experiments über die Dipolantwort eines einzelnen Elektrons in einem Heliumatom kann die beobachtete Änderung auf aus der Atomphysik bekannte Phänomene zurückgeführt werden, nämlich die AC-Stark-Verschiebung und lichtinduzierte Zustände. Insbesondere wird die beobachtete Oszillation pro NIR-Halbzyklus Quantenpfadinterferenzen, die in lichtinduzierten Zuständen auftreten, zugeschrieben. Das Experiment dieser Arbeit ist eines der Ersten, das eine Elektronendynamik im Attosekundenbereich in einzelnen Nanopartikeln durch kohärente Lichtstreuung nachweist. Damit öffnen sich neue Möglichkeiten zur zeitlich und räumlich aufgelösten Untersuchung elektronischer Prozesse in kondensierter Materie auf der Nanoskala.

This study investigates loudness perception in real-world contexts using predictors related to the sound, situation, or person. In the study, 105 participants recorded 6594 sound environments in their homes, which were then evaluated based on the Experience Sampling Method. Hierarchical linear regressions using a loudness level based on ISO 532-1 allowed for obtaining the best model fits for predicting perceived loudness and explaining the highest variance. LAeq and LAF5 provided comparable results and may require less computational effort. However, the analysis shows that only one-third of the variance explained by fixed effects was attributable to the loudness level. Sixteen percent stemmed from perceived properties of the soundscape; 1% were attributable to relatively temporally stable, person-related predictors like participants' age; non-auditory situational predictors made no additional contribution. The results thus did not confirm previous findings on loudness perception under laboratory conditions, emphasizing the importance of the situational context. Along with the current paper, a comprehensive dataset, including the assessed person-related, situational, and sound-related measures as well as LAeq time-series and third-octave spectrograms, is provided to enable further research on sound perception, indoor soundscapes, and emotion.

The aim of molecular coarse-graining approaches is to recover relevant physical properties of the molecular system via a lower-resolution model that can be more efficiently simulated. Ideally, the lower resolution still accounts for the degrees of freedom necessary to recover the correct physical behavior. The selection of these degrees of freedom has often relied on the scientist’s chemical and physical intuition. In this article, we make the argument that in soft matter contexts desirable coarse-grained models accurately reproduce the long-time dynamics of a system by correctly capturing the rare-event transitions. We propose a bottom-up coarse-graining scheme that correctly preserves the relevant slow degrees of freedom, and we test this idea for three systems of increasing complexity. We show that in contrast to this method existing coarse-graining schemes such as those from information theory or structure-based approaches are not able to recapitulate the slow time scales of the system.

N2 can be stepwise converted in silico into one molecule NH3 and a secondary amide with a bond activator molecule consisting only of light main group elements. The proposed N2-activating pincer-related compound carries a silyl ion (Si(+)) center as well as three Lewis acidic (–BF2) and three Lewis basic (–PMe2) sites, providing an efficient binding pocket for gaseous N2 within the framework of intramolecular frustrated Lewis pairs (FLP). In addition, it exhibits supportive secondary P–B and F…B contacts, which stabilize the structure. In the PSi(+)–N–N–BP environment the N≡N triple bond is extended from 1.09 Å to remarkable 1.43 Å, resembling a N–N single bond. The strongly activated N–N-fragment is prone to subsequent hydride addition and protonation steps, resulting in the energy efficient transfer of two hydrogen equivalents. The next hydride added causes the release of one molecule NH3, but leaves the ligand system as poisoned R3Si(+)–NH2–PMe2 or R3Si(+)-NH3 dead-end states behind. The study indicates that approximately tetrahedral constrained SiBP2-pockets are capable to activate N2, whereas the acid-rich SiB3- and SiB2P-pocktes, as well as the base-rich SiP3-pockets fail, hinting towards the high relevance of the acid-base proportion and relative orientation. The electronic structure of the N2-activated state is compared to the corresponding state of a recently published peri-substituted bond activator molecule featuring a PSi(+)–N–N–Si(+)P site (Mebs & Beckmann 2022).

Density modelling is the task of learning an unknown probability density function from samples, and is one of the central problems of unsupervised machine learning. In this work, we show that there exists a density modelling problem for which fault-tolerant quantum computers can offer a super-polynomial advantage over classical learning algorithms, given standard cryptographic assumptions. Along the way, we provide a variety of additional results and insights, of potential interest for proving future distribution learning separations between quantum and classical learning algorithms. Specifically, we (a) provide an overview of the relationships between hardness results in supervised learning and distribution learning, and (b) show that any weak pseudo-random function can be used to construct a classically hard density modelling problem. The latter result opens up the possibility of proving quantum-classical separations for density modelling based on weaker assumptions than those necessary for pseudo-random functions., 15 pages, one figure