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Abstract Mesoscale physics bridges the gap between the microscopic degrees of freedom of a system and its large-scale continuous behavior and highlights the role of a few key quantities in complex and multiscale phenomena, like dynamin-driven fission of lipid membranes. The dynamin protein wraps the neck formed during clathrin-mediated endocytosis, for instance, and constricts it until severing occurs. Although ubiquitous and fundamental for life, the cooperation between the GTP-consuming conformational changes within the protein and the full-scale response of the underlying lipid substrate is yet to be unraveled. In this work, we build an effective mesoscopic model from constriction to fission of lipid tubules based on continuum membrane elasticity and implicitly accounting for ratchet-like power strokes of dynamins. Localization of the fission event, the overall geometry, and the energy expenditure we predict comply with the major experimental findings. This bolsters the idea that a continuous picture emerges soon enough to relate dynamin polymerization length and membrane rigidity and tension with the optimal pathway to fission. We therefore suggest that dynamins found in in vivo processes may optimize their structure accordingly. Ultimately, we shed light on real-time conductance measurements available in literature and predict the fission time dependency on elastic parameters.

Hyperbolic metamaterial (HMM) is a unique type of anisotropic material that can exhibit metal and dielectric properties at the same time. This unique characteristic results in it having unbounded isofrequency surface contours, leading to exotic phenomena such as spontaneous emission enhancement and applications such as super-resolution imaging. However, at optical frequencies, HMM must be artificially engineered and always requires a metal constituent, whose intrinsic loss significantly limits the experimentally accessible wave vector values, thus negatively impacting the performance of these applications. The need to reduce loss in HMM stimulated the development of the second-generation HMM, termed active HMM, where gain materials are utilized to compensate for metal’s intrinsic loss. With the advent of topological photonics that allows robust light transportation immune to disorders and defects, research on HMM also entered the topological regime. Tremendous efforts have been dedicated to exploring the topological transition from elliptical to hyperbolic dispersion and topologically protected edge states in HMM, which also prompted the invention of lossless HMM formed by all-dielectric material. Furthermore, emerging twistronics can also provide a route to manipulate topological transitions in HMMs. In this review, we survey recent progress in topological effects in HMMs and provide prospects on possible future research directions.

Placed in cavity resonators with three-dimensionally confined electromagnetic wave, the interaction between quasiparticles in solids can be induced by exchanging virtual cavity photons, which can have a nonlocal characteristic. Here, we investigate the possibility of utilizing this nonlocality to realize the remote control of the topological transition in mesoscopic moiré superlattices at full filling (one electron/hole per supercell) embedded in a split-ring terahertz electromagnetic resonator. We show that gate tuning one moiré superlattice can remotely drive a topological band inversion in another moiré superlattice not in contact but embedded in the same cavity. Our study of remote on/off switching of a topological transition provides a paradigm for the control of material properties via cavity vacuum fields. [ABSTRACT FROM AUTHOR]

In this paper, the tensile deformation behaviors of polycrystals after relaxation were studied using the phase-field-crystal (PFC) method. Here, the free energy density map characterized the 2D energy distribution of atomic configuration effectively. The application of the Read–Shockley equation distinguished high-energy grain boundary (HEGB) and low-energy grain boundary (LEGB) in large-angle grain boundary (LAGB), and they demonstrated different migration behaviors at the early and later stages. The behaviors of small-angle grain boundary (SAGB), including its migration and grains' rotation, were also studied. Two different mechanisms of dislocation emission and absorption were explored, which demonstrates the possibility of dislocation elevating interfacial energy. The simulated results on the topological transition of grain boundaries prompted us to propose the thinking about the applications of the Neumann–Mullins law and Euler formula. [ABSTRACT FROM AUTHOR]

Early studies on water - n -alkane - ionic surfactant microemulsions provide first hints for the possible existence of a foam-like nanostructure, i.e. a dense packing of polyhedral nanometer-sized water droplets separated by a thin layer of a continuous oil phase. Indeed, we found a foam-like structure in the system water/NaCl - hexyl methacrylate (C 6 MA) - dioctyl sulfosuccinate sodium salt (AOT). We were able to locate an isotropic one-phase channel, the L 3 phase, emanating from the pseudo-binary system water/NaCl - AOT at ambient temperature and extending towards lower NaCl content with increasing oil content. We showed in our previous work that already upon addition of small amounts of oil to the L 3 phase the conductivities become very low and the viscosities very high. Freeze fracture electron microscopy allowed us to visualize the anticipated foam-like nanostructure. To complement our previous work, we investigated the structural transition in the L 3 channel by NMR self-diffusion measurements. The new data unambiguously confirm the existence of a foam-like structure. Based on this confirmation we offer an explanation for the topological transition to a foam-like structure, which one can also consider as a "super-swollen reverse micellar phase" – the first of its kind reported so far. [Display omitted] • First NMR self-diffusion measurements in the L 3 phase of the system water/NaCl ‑ hexyl methacrylate - AOT. • On adding very small amounts of oil the water-continuous sponge-like becomes an oil-continuous foam-like structure. • NMR data unambiguously confirm the existence of a foam-like structure on the water-rich side of the L 3 channel. • First study in which an explanation for the topological transition is given. [ABSTRACT FROM AUTHOR]

In a β‐Mn‐type chiral magnet Co9Zn9Mn2, it is demonstrated that the magnetic field‐driven collapse of a room temperature metastable topological skyrmion crystal (SkX) passes through a regime described by a partial topological charge inversion. Using Lorentz transmission electron microscopy, the magnetization distribution is observed directly as the magnetic field is swept antiparallel to the original skyrmion core magnetization, that is, negative magnetic fields. Due to the topological stability of skyrmions, a direct transition of the metastable SkX to the equilibrium helical state is avoided for increasingly negative fields. Instead, the metastable SkX gradually transforms into giant magnetic bubbles separated by 2π domain walls. Eventually these large structures give way to form a near‐homogeneously magnetized medium that unexpectedly hosts a low density of isolated skyrmions with inverted core magnetization, and thus a total topological charge of reduced size and opposite sign compared with the initial state. A similar phenomenon has been observed previously in systems hosting ordered lattices of magnetic bubbles stabilized by the dipolar interaction and called "topological melting." With support from numerical calculations, it is argued here that the observed regime of partial topological charge inversion has its origin in the topological protection of the starting metastable skyrmion state. [ABSTRACT FROM AUTHOR]

Heterostructures composed of graphene and molybdenum trioxide (MoO 3 ) can support in-plane hybrid polaritons in the infrared. The isofrequency contour for these subwavelength polaritons can exhibit a quasi-flat region when the topological transition occurs as the doping level of graphene is tuned. Such a topological transition can be useful for optical sensing and imaging at nanoscale. Here, by analyzing electron energy-loss spectroscopy (EELS), we theoretically demonstrate that free-electron-photon interactions in the heterostructure can be enhanced due to this quasi-flat region. Moreover, the free-electron-photon interaction is sensitive to the electron trajectory and is robust against certain types of defects in the structure. Furthermore, we show that the free-electron-photon interaction can undergo an ultrafast subpicosecond modulation by optical pumping and heating of graphene. Our findings may pave the way toward dynamical electron beam shaping, free-electron-based quantum light sources, and quantum sensing.

Anisotropic plasmonic surface supports elliptic, hyperbolic and even flattened polaritons, which is quite interesting for the diffractionless and highly collimated propagation of infrared light at the nanoscale. However, direct real-space near-field observation of anisotropic plasmons as well as frequency dependent topological transitions in natural materials have not been realized. In this paper, we theoretically investigate real-space anisotropic plasmons in WTe2 thin films by using a phenomenological cavity model, anisotropic near-field plasmonic images with specific interference patterns and isofrequency curves in momentum space have been demonstrated. Due to the frequency selective forbidden of plasmons along b axis, a topological transition from the elliptic to the hyperbolic regime is manifested. Moreover, the plasmons as well as topological transition present significant electrostatic-gating tunability. Our studies provide new insights into WTe2 based plasmonic components for the manipulation of plasmon propagation, which capable of tailoring anisotropic two-dimensional light confinement in the far-infrared regime and can be applied to investigate other anisotropic materials.

Hyperbolic metasurfaces with unique dispersion properties can manipulate light–matter interactions according to the demands. However, due to their inherent physical properties, topological transitions (flat bands) exist only in the orthogonal directions, which greatly limit their application. Here, we unveil rich dispersion engineering and topological transitions in hyperbolic metasurfaces. Based on the effective medium theory, the rotation matrix is introduced into the dispersion relation to explain the distorted energy band diagrams, iso-frequency contours and higher-order multi-dipoles of the novel twisted metasurfaces, thereby forming multi-directional topological transitions and surface plasmon polariton propagation. Furthermore, we develop an integrated model to realize new dual-channel negative refraction and nondiffraction negative refraction. The phenomena observed in the experiments match well with the simulations, which proves that the designed metasurfaces make new types of negative refraction possible and will help to overcome the diffraction limit. The hyperbolic metasurfaces presented here exhibit exceptional capabilities for designing microscopes with a super lens at the molecular level, concealment of military aircraft, invisibility cloaks and other photonic devices with higher transmission efficiency.

Recently, linear-crossing metamaterials (LCMMs) in the hyperbolic topological transition of iso-frequency contour, have attracted people’s great attention. Due to the novel linear dispersion, LCMM provides a new platform to control and enhance the light-matter interactions, such as all-angle negative refraction, filters, super-lens, etc. However, the narrow-band working frequency is currently the major limitation in LCMMs. In this work, we propose two methods to realize multiple linear-crossing metamaterials (MLCMMs), including a basic Drude-Lorenz model and an actual step-like multilayer structure. Especially, in order to identify the designed two kinds of MLCMMs, we numerically demonstrate the unique beam splitting and directional refraction of MLCMM at different frequencies. Our findings may not only provide a new platform for the fundamental study of LCMM, but also facilitate some broadband applications.

In this paper, the tensile deformation behaviors of polycrystals after relaxation were studied using the phase-field-crystal (PFC) method. Here, the free energy density map characterized the 2D energy distribution of atomic configuration effectively. The application of the Read–Shockley equation distinguished high-energy grain boundary (HEGB) and low-energy grain boundary (LEGB) in large-angle grain boundary (LAGB), and they demonstrated different migration behaviors at the early and later stages. The behaviors of small-angle grain boundary (SAGB), including its migration and grains’ rotation, were also studied. Two different mechanisms of dislocation emission and absorption were explored, which demonstrates the possibility of dislocation elevating interfacial energy. The simulated results on the topological transition of grain boundaries prompted us to propose the thinking about the applications of the Neumann–Mullins law and Euler formula.

Recently, topological chains have attracted extensive attention because of their simple structure, rich physics and important applications. In this work, we theoretically and experimentally uncover that the abundant topological phases of periodic trimer chain composed of one kind of meta-atom, namely split-ring resonators (SRRs), can be flexibly controlled by tunning the rotation angle of SRRs. On the one hand, we study the rotation controlled phase transition between two topological distinguished trimer chains with inversion symmetry. The generation of symmetric edge states can be easily controlled in this phase transition. On the other hand, the topological phases of the trimer chain broken inversion symmetry is demonstrated. Especially, the rotation controlled asymmetric edge states are observed in this process. So, rotation provides a new degree of freedom to manipulate edge states in the trimer chain composed of SRRs. The results in this work not only provide a flexible way to observe controlled edge states, but also provide a good research platform for designing other topological models with complex coupling distributions. [ABSTRACT FROM AUTHOR]

The CoSi family hosts unconventional topological nodes with nonzero Chern numbers. The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes. Here, using angle-resolved photoemission spectroscopy, we have systematically investigated the (001) surface states of pristine and Ni-doped CoSi. The surface states form saddle-like band structures at/near the time-reversal invariant point near the Fermi level. The Fermi arcs undergo consecutive Lifshitz transitions at the saddle points X ¯ , leading to changes of the Fermi arc configuration. As the density of states has a van Hove singularity at the saddle points, exotic many-body physical phenomena may emerge accompanied by the topological transitions of surface Fermi arcs. [ABSTRACT FROM AUTHOR]

In particular, for the TM mode, the dispersion relation can be written as: HT ht Graph (2)where I k i SB 0 sb is the wave-vector in free space, and I k i SB x sb , I k i SB y sb are the I x i and I y i components of the wave-vector, respectively. In the case of 0° < I i < 45° and HT ht , the relative permittivity obtained from EMT shows good agreement with Eq. (7). When the rotation angle I i = 0° and HT ht , the effective permittivity only has diagonal terms, which successfully predict the effective medium properties. When I i = 90°, the dispersion relation Eq. (5) changes to: HT ht Graph (6) We can clearly see that when the structural unit rotates 90°, the IFC rotates 90° accordingly. [Extracted from the article]

Synthesis of one‐dimensional nanofibers with distinct topological (higher‐order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non‐uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post‐polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene‐embedded rigid π‐conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV‐light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible‐light irradiation followed by aging to restore fully folded structures. [ABSTRACT FROM AUTHOR]

Multicolor carbon dot (CD)‐based nanomaterials offer a variety of opportunities for potential applications in bioimaging, optoelectronic devices, and information security. However, it still remains a challenge to modulate the conjugated π‐structure of CDs to achieve multicolor room‐temperature phosphorescence (RTP). Herein, the authors present a strategy based on thermally driven amorphous−crystalline phase transition to achieve multicolor carbonized polymer dots (CPDs) with the emission color tunable from green to orange‐red. This is the first report on multicolor RTP emission from CDs by means of thermal stimulus. Further investigations reveal that the formation of self‐protective covalently crosslinked frameworks and codoping of multiple heteroatoms play a crucial role in the production of RTP. RTP color tunability can be attributed to different crystalline contents of the conjugated π‐domain within CPDs. Potential application of the developed CPDs as printable and writable security inks for advanced multilevel anti‐counterfeiting and encryption is demonstrated. This work paves a path for the development of multicolor RTP materials and suggests great potential of CDs in exploiting novel optical materials toward intriguing applications. [ABSTRACT FROM AUTHOR]

The propagation properties of electromagnetic waves depend on media dispersion in momentum space, which can be characterized using isofrequency contours (IFCs). Normal linear‐crossing metamaterials (NLCMMs), which undergo a new type of topological transition between two kinds of hyperbolic media, are attracting attention because of their potential as a new avenue for controlling light propagation and verifying unusual phenomena involving zero‐index and hyperbolic media. Herein, the rotation of the optical axis is treated as a new degree of freedom and a tilted linear‐crossing metamaterial (TLCMM) is theoretically proposed. Upon rotating the optical axis angle such that it is equal to the cone angle, it is found that this special TLCMM has the shape of a type‐III Dirac cone, in condensed matter physics. Boundary conditions and the causality law are used to reveal that electromagnetic waves in this critical TLCMM can achieve abnormal refraction without reflection and filtering. Moreover, these phenomena are observed experimentally in a planar circuit‐based system. The results regarding the manipulation of electromagnetic waves may enable their use in planar‐integrated photonics, including for directional propagation, cloaking, and switching.

We carried out first-principles calculations to investigate the electronic properties of the monolayer blue phosphorene (BlueP) decorated by the group-IVB transition-metal adatoms (Cr, Mo and W), and found that the Cr-decorated BlueP is a magnetic half metal, while the Mo- and W-decorated BlueP are semiconductors with band gaps smaller than 0.2 eV. Compressive biaxial strains make the band gaps close and reopen, and band inversions occur during this process, which induces topological transitions in the Mo-decorated BlueP (with strain of −5.75%) and W-decorated BlueP (with strain of −4.25%) from normal insulators to topological insulators (TIs). The TI gap is 94 meV for the Mo-decorated BlueP and 218 meV for the W-decorated BlueP. Such large TI gaps demonstrate the possibility to engineer topological phases in the monolayer BlueP with transition-metal adatoms at high temperature. [ABSTRACT FROM AUTHOR]

Abstract We investigate the structure attained by neutron star matter with proton to neutron ratios ranging from x = 0.1 to 0.5, densities in the range of 0.02 fm−3 < ρ < 0.085 fm−3, and temperatures T < 4 MeV. In particular we study the pasta shapes and the phase changes previously observed in nuclear matter, as well as the behavior of the symmetry energy. We corroborate the existence of homogeneous to non-homogeneous phase transitions, and the different values of the symmetry energy at different densities and temperatures. Highlights • We clarified the matter on the relevance of quantal delocalization. • We made clear that the parameters of the screening Coulomb potential ensure the stability of the pasta properties. • We improved the Esym computation (see Section 2.2.2 and Appendix A) according to the reviewers suggestions. [ABSTRACT FROM AUTHOR]

Abstract The fidelity between two infinitesimally close states and the fidelity susceptibility of a system are known to detect quantum phase transitions. Here we show that the k -space fidelity between two states far from each other and taken deep inside (bulk) of two phases, generically vanishes at the k-points where there are gapless points in the energy spectrum that give origin to the lines (edges) separating the phases in the phase diagram. We consider a general case of two-band models and present a sufficient condition for the existence of gapless points, given there are pairs of parameter points for which the fidelity between the corresponding states is zero. By presenting an explicit counter-example, we show that the sufficient condition is not necessary. Further, we show that, unless the set of parameter points is suitably constrained, the existence of gapless points generically implies accompanied pairs of parameter points with vanishing fidelity. Also, we show the connection between the vanishing fidelity and gapless points on a number of concrete examples (topological triplet superconductor, topological insulator, 1 d Kitaev model of spinless fermions, BCS superconductor, Ising model in a transverse field, graphene and Haldane Chern insulator), as well as for the more general case of Dirac-like Hamiltonians. We also briefly discuss the relation between the vanishing fidelity and gapless points at finite temperatures. [ABSTRACT FROM AUTHOR]

In this paper, plasmonic responses of phosphorene in the presence of strain and doping have been systematically investigated. Based on density functional theory, permittivities include both the intraband and interband transitions of electrons have been calculated. Due to the modification of the band structure, significantly higher Drude plasma frequency has been observed along the zigzag direction, other than the armchair direction as in the usual case. The resulting unusual plasmonic responses change their anisotropy, both in the elliptic as well as the hyperbolic regimes. Based on our calculations, positive strain as large as 5% along the zigzag direction can even lead to so-called reversed hyperbolic plasmonic responses. The k -surfaces of the plasmonic modes in extended monolayer have been analytically solved, and it is found that actively switching the topology (between elliptic and hyperbolic regimes) of the plasmonic responses by changing the Fermi level is possible in phosphorene at certain frequencies. In the end, a simple model has been proposed to describe such plasmonic responses in the infrared and the parameters of the model have been listed in tables which can be used directly in calculating the permittivities. Our studies may extend the scope of existing investigations of phosphorene plasmons and lead to band engineering as a way to control plasmons in two-dimensional materials.

Abstract Cold and isospin-symmetric nuclear matter at sub-saturation densities is known to form the so-called pasta structures, which, in turn, are known to undergo peculiar phase transitions. Here we investigate if such pastas and their phase changes survive in isospin asymmetric nuclear matter, and whether the symmetry energy of such pasta configurations is connected to the isospin content, the morphology of the pasta and to the phase transitions. We find that indeed pastas are formed in isospin asymmetric systems with proton to neutron ratios of x = 0.3 , 0.4 and 0.5, densities in the range of 0.05 fm − 3 < ρ < 0.08 fm − 3 , and temperatures T < 2 MeV. Using tools (such as the caloric curve, Lindemann coefficient, radial distribution function, Kolmogorov statistic, and Euler functional) on the composition of the pasta, determined the existence of homogeneous structures, tunnels, empty regions, cavities and transitions among these regions. The symmetry energy was observed to attain different values in the different phases showing its dependence on the morphology of the nuclear matter structure. [ABSTRACT FROM AUTHOR]

Featured Application: Active optical devices. Topological transition of the iso-frequency contour (IFC) from a closed ellipsoid to an open hyperboloid provides unique capabilities for controlling the propagation of light. However, the ability to actively tune these effects remains elusive, and the related experimental observations are highly desirable. Here, a tunable electric IFC in a periodic structure composed of graphene/dielectric multilayers is investigated by tuning the chemical potential of the graphene layer. Specially, we present the actively controlled transportation in two kinds of anisotropic zero-index media containing perfect electric conductor/perfect magnetic conductor impurities. Finally, by adding variable capacitance diodes into a two-dimensional transmission-line system, we present an experimental demonstration of the actively controlled magnetic topological transition of dispersion based on electrically controllable metamaterials. With the increase in voltage, we measure the different emission patterns from a point source inside the structure and observe the phase-transition process of IFCs. The realization of an actively tuned topological transition will open up a new avenue in the dynamical control of metamaterials. [ABSTRACT FROM AUTHOR]

The significance of topological phases has been widely recognized in the community of condensed matter physics. The well controllable quantum systems provide an artificial platform to probe and engineer various topological phases. The adiabatic trajectory of a quantum state describes the change of the bulk Bloch eigenstates with the momentum, and this adiabatic simulation method is however practically limited due to quantum dissipation. Here we apply the 'shortcut to adiabaticity' (STA) protocol to realize fast adiabatic evolutions in the system of a superconducting phase qubit. The resulting fast adiabatic trajectories illustrate the change of the bulk Bloch eigenstates in the Su-Schrieffer-Heeger (SSH) model. A sharp transition is experimentally determined for the topological invariant of a winding number. Our experiment helps identify the topological Chern number of a two-dimensional toy model, suggesting the applicability of the fast adiabatic simulation method for topological systems. [ABSTRACT FROM AUTHOR]

The ground-state features of a mixed-spin Heisenberg bond-alternating chain with unit cell consisting of spin-1/2 and general spin- S dimers are investigated using density matrix renormalization group (DMRG) calculations. Similar spin units are considered to interact via an isotropic antiferromagnetic coupling constant J 1 , while an exchange constant J 2 accounts for the interaction between distinct spin units. With increasing values of an external magnetic field, the system presents a sequence of magnetic-field-driven transitions between gapped plateau and gapless spin-liquid phases. At zero field, a quantum phase transition emerges between two topologically distinct gapped phases at a quantum critical point J c = (J 2 / J 1) | c at which the energy spin-gap closes. We employ a tangential finite-size scaling analysis of the relevant energy gap to precisely locate the quantum critical point and to estimate the correlation length critical exponent for several magnitudes of the spin S. While the critical value of the coupling constant ratio decreases with S , the scaling of the correlation length presents a universal power-law with a logarithmic correction scaling. • A bond alternating quantum spin chain with coupled dimers is considered. • The system presents a topological quantum phase transition at zero field. • A tangential finite-size scaling analysis of DMRG data unveils the relevant critical features. • The critical exchange ratio depends on the relative magnitude of the spin dimers. • The localization length is shown to present a logarithmic correction to power-law scaling. [ABSTRACT FROM AUTHOR]

Holey layered HEO nanocrystals with surface FLP sites have been synthesized via a temperature-variable topological transition. Merits of high-entropy oxides and nanoscale effects are favored yielding a superior catalytic performance toward the transfer hydrogenation (CTH) reaction of biomass-derived carbonyl compounds at mild conditions. Mechanistic investigation indicates that the formation of active regions between FLPs provides a stronger driving force for dissociating alcohols and activating the carbonyl groups of substrates, accounting for the enhanced catalytic activity. [Display omitted] • Holey layered high entropy oxide (HEO) nanocrystals with abundant frustrated Lewis pairs (FLPs) have been synthesized. • Combination of HEO properties and nanoscale effect drives FLPs concentrations of as-obtained catalyst up to 585.4 μmol/g. • Catalysts display superior catalytic activity and cycling performance toward the CTH reaction under mild conditions. • FLPs provide stronger driving forces for dissociating alcohols and activating the carbonyl groups of substrates. • Direct hydrogen transfer dominates the catalytic reaction over holey lamellar HEO catalysts. Creating frustrated Lewis pairs (FLPs) on stable high-entropy oxides (HEOs) is a new challenge, and also an uncultivated field in catalysis. Herein, holey layered HEO spinel nanocrystals with rich FLPs were synthesized via a temperature-driven topological transition. The FLPs on the surface of HEO spinel nanocrystals are created by oxygen vacancies (Lewis acid sites) and proximal surface hydroxyls or surface lattice oxygen (Lewis base sites). Rich FLPs furnish HEO nanocrystals a superior activity towards the catalytic transfer hydrogenation reaction of biomass-derived carbonyl compounds at mild conditions. The active regions in between FLPs provide a strong driving force for dissociating alcohols and activating carbonyl groups of substrates, as evidenced by the attenuated total reflectance-infrared spectroscopy (ATR-IR) analysis, which enhances the catalytic activity. This work develops a new kind of hydrogenation catalysts and provides a perspective for creating solid FLPs. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions, particular those without the support of external magnetic fields over a wide temperature region, are promising as alternative spintronic units to overcome the fundamental size limitation of conventional magnetic bits. In this study, we use in situ Lorentz microscope to directly demonstrate the generation and sustainability of robust biskyrmion lattice at zero magnetic field over a wide temperature range of 16-338 K in MnNiGa alloy. This procedure includes a simple field-cooling manipulation from 360 K (higher than Curie temperature TC ~ 350 K), where topological transition easily occurs by adapting the short-range magnetic clusters under a certain magnetic field. The biskyrmion phase is favored upon cooling below TC. Once they are generated, the robust high-density biskyrmions persist even after removing the external magnetic field due to the topological protection and the increased energy barrier. [ABSTRACT FROM AUTHOR]

The dynamical property of electrons with the tilted Dirac cone was examined using the tilted Weyl equation. The polarization function exhibits cusps and nonmonotonic structures by varying both the frequency and the momentum. A pair of tilted Dirac cones exhibits a new plasmon for the intermediate magnitude of momentum owing to the combined effects of two tilted cones. Dirac electrons with the zero-gap state (ZGS) in organic conductor α-(BEDT-TTF)2I3 are examined by calculating the Berry curvature, which displays the peak structure for a pair of Dirac particles between the conduction band and the valence band. The ZGS is theoretically predicted for α-(BEDT-TTF)2NH4Hg(SCN)4 under uniaxial pressure. Examining the band structure of the stripe charge ordered state of α-(BEDT-TTF)2I3 under pressure, we have found a topological transition from a conventional insulator to a new phase of a pair of Dirac electrons with a finite mass. Further, investigating the zero-energy (N = 0) Landau level under a strong magnetic field, we propose ferromagnetism breaking the SU(2) valley-pseudo-spin symmetry, and the phase fluctuations of the order parameters leading to Kosterlitz-Thouless transition at lower temperatures.

In this study, a Dirac cone is yielded at the corner of the Brillouin zone of a two-dimensional solid phononic crystal, which consists of a triangular array of hexagonal steel with a trilobal hole drilled in the center. With the rotation of the trilobal hole, the Dirac degeneracy switches between the deterministic form and accidental form. Every Dirac point is the critical state of a topological phase transition process, which occurs six times within an angular period of $120^\circ .$ This structure offers a flexible way to achieve topological transitions and provides multiple routes to construct an interface that supports valley-dependent edge states between two topologically distinct PCs. The associated backscattering suppressed wave propagation along the multiple curved interface channels is also demonstrated. In addition, our design shows the robust propagation of topological interface states against the perturbation of the structure. This study could potentially be significant in the design of acoustic devices for practical applications, such as acoustic signal lossless transport and tunable multi-channel sound transmission.

Topological transition of the iso-frequency contour (IFC) from a closed ellipsoid to an open hyperboloid provides unique capabilities for controlling the propagation of light. However, the ability to actively tune these effects remains elusive, and the related experimental observations are highly desirable. Here, a tunable electric IFC in a periodic structure composed of graphene/dielectric multilayers is investigated by tuning the chemical potential of the graphene layer. Specially, we present the actively controlled transportation in two kinds of anisotropic zero-index media containing perfect electric conductor/perfect magnetic conductor impurities. Finally, by adding variable capacitance diodes into a two-dimensional transmission-line system, we present an experimental demonstration of the actively controlled magnetic topological transition of dispersion based on electrically controllable metamaterials. With the increase in voltage, we measure the different emission patterns from a point source inside the structure and observe the phase-transition process of IFCs. The realization of an actively tuned topological transition will open up a new avenue in the dynamical control of metamaterials.

The helical spin texture on the surface of topological crystalline insulators (TCI) makes these materials attractive for application in spintronics. In this work, spin-polarization and electronic structure of surface states of (111)-oriented Pb 1 − x Sn x Se TCI epitaxial films are examined by angle- as well as spin-resolved photoemission spectroscopy (SR-ARPES). High-quality epilayers with various Sn content are grown by the molecular beam epitaxy (MBE) method. Topological-normal insulator transition manifesting itself as band gap opening is observed. It is shown that the gap opening can be induced not only by changing the Sn content of the epilayer but also depositing a transition metal (TM) on its surface. In the latter case, the observed gaping of the surface states is caused by change in surface composition and not by magnetism. We also show that helical spin polarization is present not only for samples of topological composition but also for trivial ones (with an open band gap). The observed spin polarization reaches a value of 30% for the in-plane spin component and is almost absent for the out-of-plane one. We believe that our work will pave the way for the application of surface states not only of topological but also normal insulators based on lead–tin chalcogenides in spin-charge conversion devices. [Display omitted] • High quality topological crystalline insulator (111) Pb 1 − x Sn x Se epilayers are grown by molecular beam epitaxy. • Helical surface states are observed by spin-resolved ARPES for both trivial and topological compositions of Pb 1 − x Sn x Se. • Deposition of transition metals on the surface of the topological crystalline insulator shifts the band inversion point. [ABSTRACT FROM AUTHOR]