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Fundamental research on two-dimensional (2D) magnetic systems based on van der Waals materials has been gaining traction rapidly since their recent discovery. With the increase of recent knowledge, it has become clear that such materials have also a strong potential for applications in devices that combine magnetism with electronics, optics, and nanomechanics. Nonetheless, many challenges still lay ahead. Several fundamental aspects of 2D magnetic materials are still unknown or poorly understood, such as their often-complicated electronic structure, optical properties, and magnetization dynamics, and their magnon spectrum. To elucidate their properties and facilitate integration in devices, advanced characterization techniques and theoretical frameworks need to be developed or adapted. Moreover, developing synthesis methods which increase critical temperatures and achieve large-scale, high-quality homogeneous thin films is crucial before these materials can be used for real-world applications. Therefore, the field of 2D magnetic materials provides many challenges and opportunities for the discovery and exploration of new phenomena, as well as the development of new applications. This Roadmap presents the background, challenges, and potential research directions for various relevant topics in the field on the fundamentals, synthesis, characterization, and applications. We hope that this work can provide a strong starting point for young researchers in the field and provide a general overview of the key challenges for more experienced researchers., Comment: 87 pages, 24 figures. Roadmap based on the discussions during the workshop on Quantum Magnetic Materials hosted by the Lorentz Centre in Leiden, the Netherlands (Oct. 2023)

In the last few years, economic agent-based models have made the transition from qualitative models calibrated to match stylised facts to quantitative models for time series forecasting, and in some cases, their predictions have performed as well or better than those of standard models (see, e.g. Poledna et al. (2023a); Hommes et al. (2022); Pichler et al. (2022)). Here, we build on the model of Poledna et al., adding several new features such as housing markets, realistic synthetic populations of individuals with income, wealth and consumption heterogeneity, enhanced behavioural rules and market mechanisms, and an enhanced credit market. We calibrate our model for all 38 OECD member countries using state-of-the-art approximate Bayesian inference methods and test it by making out-of-sample forecasts. It outperforms both the Poledna and AR(1) time series models by a highly statistically significant margin. Our model is built within a platform we have developed, making it easy to build, run, and evaluate alternative models, which we hope will encourage future work in this area.

The significance of Mendeleev's periodic table extends beyond the classification of elements; it lies in its remarkable predictive power for discovering new elements and properties, revealing the underlying symmetrical patterns of nature that were only fully understood with the advent of quantum mechanics. Fundamental material properties, such as electron transport and magnetism, are also governed by crystal symmetry. In particular, spin transport depends on the spin polarization of electronic states, and recently discovered materials where the electron spin polarization is independent of momentum - a property known as a persistent spin texture (PST) - promise extended spin lifetime and efficient spin accumulation. In this paper, we establish the general conditions for the existence of symmetry-protected PST in bulk crystals. By systematically analyzing all 230 crystallographic space groups, similar to elements in the periodic table, we demonstrate that PST is universally present in all nonmagnetic solids lacking inversion symmetry. Using group theory, we identify the regions within the Brillouin zone that host PST and determine the corresponding directions of spin polarization. Our findings, supported by first-principles calculations of representative materials, open the route for discovering robust spintronic materials based on PST.

Van der Waals (vdW) heterostructure of two-dimensional (2D) quantum materials offers a promising platform for efficient control of magnetization dynamics for non-volatile spin-based devices. However, energy-efficient field-free spin-orbit torque (SOT) switching and spin dynamics experiments to understand the basic SOT phenomena in all-2D vdW heterostructures are so far lacking. Here, we demonstrate energy-efficient field-free spin-orbit torque (SOT) switching and tunable magnetization dynamics in a vdW heterostructure comprising out-of-plane magnet Fe3GaTe2 and topological Weyl semimetal TaIrTe4. We measured the non-linear second harmonic Hall signal in TaIrTe4 /Fe3GaTe2 devices to evaluate the SOT-induced magnetization dynamics, which is characterized by a large and tunable out-of-plane damping-like torque. Energy-efficient and deterministic field-free SOT magnetization switching is achieved at room temperature with a very low current density. First-principles calculations unveil the origin of the unconventional charge-spin conversion phenomena, considering the crystal symmetry and electronic structure of TaIrTe4. These results establish that all-vdW heterostructures provide a promising route to energy-efficient, field-free, and tunable SOT-based spintronic devices.

Cross-Modal Retrieval (CMR), which retrieves relevant items from one modality (e.g., audio) given a query in another modality (e.g., visual), has undergone significant advancements in recent years. This capability is crucial for robots to integrate and interpret information across diverse sensory inputs. However, the retrieval space in existing robotic CMR approaches often consists of only one modality, which limits the robot's performance. In this paper, we propose a novel CMR model that incorporates three different modalities, i.e., visual, audio and tactile, for enhanced multi-modal object retrieval, named as VAT-CMR. In this model, multi-modal representations are first fused to provide a holistic view of object features. To mitigate the semantic gaps between representations of different modalities, a dominant modality is then selected during the classification training phase to improve the distinctiveness of the representations, so as to improve the retrieval performance. To evaluate our proposed approach, we conducted a case study and the results demonstrate that our VAT-CMR model surpasses competing approaches. Further, our proposed dominant modality selection significantly enhances cross-retrieval accuracy., Comment: 7 pages, 6 figures, accepted to the 2024 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2024)

Efficient conversion between charge currents and spin signals is crucial for realizing magnet-free spintronic devices. However, the strong spin-orbit coupling that enables such a conversion, causes rapid relaxation of spins, making them difficult to transport over large length scales. Here, we show that spin-momentum entanglement at the Fermi surface of chiral tellurium crystals leads to the appearance of slow collective relaxation modes. These modes, called relaxons, resemble the persistent spin helix, a collective spin-wave excitation with extended lifetime observed in quantum wells. The slow relaxons dominate the electrically generated spin and orbital angular momentum accumulation in tellurium and make it possible to combine a very high 50% conversion efficiency with a long spin lifetime. These results, obtained from the exact solution of the Boltzmann transport equation, show that chiral crystals can be used for highly efficient generation and transmission of spin signals over long distances in spintronic devices., Comment: 9 pages, 4 figures

Topological insulators have been studied intensively over the last decades. Among these materials, three-dimensional (3D) zirconium pentatelluride (ZrTe$_5$) stands out as one of the most intriguing for both theoretical and experimental studies because of its diverse range of distinct topological phases. In this work, we employ density functional theory to study the electronic structure and quantum oscillations exhibited by various topological phases of 3D bulk ZrTe$_5$. We have discovered that by analyzing combined patterns in band structures, Fermi surfaces, and Shubnikov-de Haas (SdH) oscillations we can determine the corresponding topological phase without relying on the conventional calculation of topological invariants or boundary state contributions. This approach facilitates the identification of topological phases in ZrTe$_5$ directly from experimental quantum oscillation measurements. Using this method, we have analyzed the entire process of topological phase transition, revealing changes in the topology of the Fermi pockets and validating the shapes deduced from the experimental data for the topological phases.

Technology is increasingly used in Nature Reserves and National Parks around the world to support conservation efforts. Endangered species, such as the Eurasian Lynx (Lynx lynx), are monitored by a network of automatic photo traps. Yet, this method produces vast amounts of data, which needs to be prepared, analyzed and interpreted. Therefore, researchers working in this area increasingly need support to process this incoming information. One opportunity is to seek support from volunteer Citizen Scientists who can help label the data, however, it is challenging to retain their interest. Another way is to automate the process with image recognition using convolutional neural networks. During the panel, we will discuss considerations related to nature research and conservation as well as opportunities for the use of Citizen Science and Machine Learning to expedite the process of data preparation, labelling and analysis., Comment: 10 pages, 11 figures, MIDI 2023 conference

The diverse and intriguing phenomena observed in twisted bilayer systems, such as graphene and transition metal dichalcogenides, prompted new questions about the emergent effects that they may host. However, the practical challenge of realizing these structures on a scale large enough for spectroscopic investigation, remains a significant hurdle, resulting in a scarcity of direct measurements of the electronic band structure of twisted transition metal dichalcogenide bilayers. Here we present a systematic nanoscale angle-resolved photoemission spectroscopy investigation of bulk, single layer, and twisted bilayer WS2 with a small twist angle of 4.4{\deg}. The experimental results are compared with theoretical calculations based on density functional theory along the high-symmetry directions {\Gamma}-K and {\Gamma}-M. Surprisingly, the electronic band structure measurements suggest a structural relaxation occurring at 4.4{\deg} twist angle, and formation of large, untwisted bilayer regions., Comment: 23 pages, 11 figures

The shape of the Fermi surface influences many physical phenomena in materials and a growing interest in how the spin-dependent properties are related to the fermiology of crystals has surged. Recently, a novel current-dependent nonlinear magnetoresistance effect, known as bilinear magnetoelectric resistance (BMR), has been shown to be not only sensitive to the spin-texture in spin-polarized non-magnetic materials, but also dependent on the convexity of the Fermi surface in topological semimetals. In this paper, we show that the temperature dependence of the BMR signal strongly depends on the crystal axis of the semimetallic MoTe${}_2$. For the a-axis, the amplitude of the signal remains fairly constant, while for the b-axis it reverses sign at about 100 K. We calculate the BMR efficiencies at 10 K to be $\chi^{J}_{A} = (100\pm3)$ nm${}^2$T${}^{-1}$A${}^{-1}$ and $\chi^{J}_{B} = (-364\pm13)$ nm${}^2$T${}^{-1}$A${}^{-1}$ for the a- and b-axis, respectively, and we find that they are comparable to the efficiencies measured for WTe${}_2$. We use density functional theory calculations to compute the Fermi surfaces of both phases at different energy levels and we observe a change in convexity of the outer-most electron pocket as a function of the Fermi energy. Our results suggest that the BMR signal is mostly dominated by the change in the Fermi surface convexity., Comment: 7 pages, 3 figures

Revived interest in lunar and planetary exploration is heralding a new era for human spaceflight, characterized by frequent strain on astronaut's mental well-being, which stems from increased exposure to isolated, confined, and extreme (ICE) conditions. Whilst Immersive Virtual Reality (IVR) has been employed to facilitate self-help interventions to mitigate challenges caused by isolated environments in several domains, its applicability in support of future space expeditions remains largely unexplored. To address this limitation, we administered the use of distinct IVR environments to crew members (n=5) partaking in a simulated lunar habitat study. Utilizing a Bayesian approach to scrutinize small group data, we discovered a significant relationship between IVR usage and a reduction in perceived stress-related symptoms, particularly those associated with asthenia (syndrome often linked to chronic fatigue and weakness; a condition characterized by feelings of energy depletion or exhaustion that can be amplified in ICE conditions). The reductions were most prominent with the use of interactive virtual environments. The 'Aesthetic Realities' - virtual environments conceived as art exhibits - received exceptional praise from our participants. These environments mark a fascinating convergence of art and science, holding promise to mitigate effects related to isolation in spaceflight training and beyond.

Incommensurate heterostructures of two-dimensional (2D) materials, despite their attractive electronic behaviour, are challenging to simulate because of the absence of translation symmetry. Experimental investigations of these structures often employ scanning tunneling microscopy (STM), however there is to date no comprehensive theory to simulate an STM image in such systems. In this paper, we present a geometry-based method to generate STM images in incommensurate van der Waals (vdW) heterostructures, which we call the moir\'e plane wave expansion model (MPWEM). We generate the STM images using a weighted sum of three image terms: the non-interacting STM images of (1) the substrate layer, (2) the adsorbate layer, and (3) a semi-empirical Fourier expansion of the moir\'e wavevectors obtained analytically which results from the interaction of (1) and (2). We illustrate and benchmark the model using selected vdW 2D systems composed of structurally and electronically distinct crystals, and show that the method reproduces experimental STM images down to angstrom-scale details. The MPWEM, thanks to its simplicity, can serve as an initial prediction tool prior to more computationally expensive calculations which are often limited by the number of atoms and the requirement of periodic supercells, and thus offers a promising class of computationally-friendly STM simulations, of high relevance in the growing field of twistronics., Comment: 12 pages, 5 figures (+ supplementary information)

The recently reported Bilinear Magnetoeletric Resistance (BMR) in novel materials with rich spin textures, such as bismuth selenide (Bi$_2$Se$_3$) and tungsten ditelluride (WTe$_2$), opens new possibilities for probing the spin textures via magneto-transport measurements. By its nature, the BMR effect is directly linked to the crystal symmetry of the materials and its spin texture. Therefore, understanding the crystallographic dependency of the effect is crucial. Here we report the observation of crystallographic-dependent BMR in thin WTe$_2$ layers and explore how it is linked to its spin textures. The linear response measured in first harmonic signals and the BMR measured in second harmonic signals are both studied under a wide range of magnitudes and directions of magnetic field, applied current and at different temperatures. We discover a three-fold symmetry contribution of the BMR when current is applied along the a-axis of the WTe$_2$ thin layer at 10 K, which is absent for when current is applied along the b-axis.

Transition metal dichalcogenides exhibit giant spin-orbit coupling, and intriguing spin-valley effects, which can be harnessed through proximity in van der Waals (vdW) heterostructures. Remarkably, due to the prismatic crystal field, the Zeeman-type band splitting of valence bands reach values of several hundreds of meV. While this effect is suppressed in the commonly studied hexagonal (H)-stacked bilayers due to the presence of inversion symmetry, the recent discovery of sliding ferroelectricity in rhombohedral (R-)stacked MX$_2$ bilayers (M=Mo, W; X=S, Se) suggests that the Zeeman effect could be present in these non-centrosymmetric configurations, making it even more intriguing to investigate how the spin-resolved bands would evolve during the phase transition. Here, we perform density functional theory calculations complemented by symmetry analysis to unveil the evolution of ferroelectricity during sliding and the behavior of Zeeman splitting along the transition path. While the evolution of the out-of-plane component of the electric polarization vector resembles the conventional ferroelectric transition, we observe significant in-plane components parallel to the sliding direction, reaching their maximum at the intermediate state. Moreover, we demonstrate that the R-stacked bilayers exhibit persistent Zeeman-type band splitting throughout the transition path, allowed by the lack of inversion symmetry. Further analysis of different stacking configurations generated by sliding along various directions confirms that the Zeeman effect in MX$_2$, primarily arising from the polarity of prismatic ligand coordination of the metal atom, is remarkably robust and completely governs the spin polarization of bands, independently of the sliding direction. This resilience promises robust spin transport in vdW based MX$_2$ bilayers, opening new opportunities for ferroelectric spintronics.

Efficient generation and manipulation of spin signals in a given material without invoking external magnetism remain one of the challenges in spintronics. The spin Hall effect (SHE) and Rashba-Edelstein effect (REE) are well-known mechanisms to electrically generate spin accumulation in materials with strong spin-orbit coupling (SOC), but the exact role of the strength and type of SOC, especially in crystals with low symmetry, has yet to be explained. In this study, we investigate REE in two different families of non-magnetic chiral materials, elemental semiconductors (Te and Se) and semimetallic disilicides (TaSi$_2$ and NbSi$_2$), using an approach based on density functional theory (DFT). By analyzing spin textures across the full Brillouin zones and comparing them with REE magnitudes calculated as a function of chemical potential, we link specific features in the electronic structure with the efficiency of the induced spin accumulation. Our findings show that magnitudes of REE can be increased by: (i) the presence of purely radial (Weyl-type) spin texture manifesting as the parallel spin-momentum locking, (ii) high spin polarization of bands along one specific crystallographic direction, (iii) low band velocities. By comparing materials possessing the same crystal structures, but different strengths of SOC, we conclude that larger SOC may indirectly contribute to the enhancement of REE. It yields greater spin-splitting of bands along specific crystallographic directions, which prevents canceling the contributions from the oppositely spin-polarized bands over wider energy regions and helps maintain larger REE magnitudes. We believe that these results will be useful for designing spintronics devices and may aid further computational studies searching for efficient REE in materials with different symmetries and SOC strengths.

The COVID-19 pandemic has stimulated the scientific world to intensify virus-related studies, aimed at the development of quick and safe ways of detecting viruses in human body, studying the virus-antibody and virus-cell interactions, and designing nanocarriers for targeted antiviral therapies. However, research on dangerous viruses can only be performed in certified laboratories that follow strict safety procedures. Thus, developing deactivated virus constructs or safe-to-use virus-like objects, which imitate real viruses and allow performing virus-related studies in any research laboratory, constitutes an important scientific challenge. One of the groups of such species are the so-called virus-like particles (VLPs). Instead of capsids with viral DNA/RNA, VLPs have synthetic cores with real virus proteins attached to them. We have developed a method for the preparation of VLPs imitating the virus responsible for the COVID-19 disease: the SARS-CoV-2. The particles have Au cores surrounded by "coronas" of S1 domains of the virus's Spike protein. Importantly, they are safe to use and specifically interact with SARS-CoV-2 antibodies. Moreover, Au cores exhibit localized surface plasmon resonance (LSPR), which makes the synthesized VLPs suitable for biosensing applications. Within our studies, the effect allowed us to visualize the interaction between the VLPs and the antibodies and identify the characteristic vibrational signals. What is more, additional functionalization of the particles with a fluorescent label revealed their potential in studying specific virus-related interactions. Notably, the universal character of the developed synthesis method makes it potentially applicable for fabricating VLPs imitating other life-threatening viruses.

Studies of structure-property relationships in spintronics are essential for the design of materials that can fill specific roles in devices. For example, materials with low symmetry allow unconventional configurations of charge-to-spin conversion which can be used to generate efficient spin-orbit torques. Here, we explore the relationship between crystal symmetry and geometry of the Rashba-Edelstein effect (REE) that causes spin accumulation in response to an applied electric current. Based on a symmetry analysis performed for 230 crystallographic space groups, we identify classes of materials that can host conventional or collinear REE. Although transverse spin accumulation is commonly associated with the so-called 'Rashba materials', we show that the presence of specific spin texture does not easily translate to the configuration of REE. More specifically, bulk crystals may simultaneously host different types of spin-orbit fields, depending on the crystallographic point group and the symmetry of the specific $k$-vector, which, averaged over the Brillouin zone, determine the direction and magnitude of the induced spin accumulation. To explore the connection between crystal symmetry, spin texture, and the magnitude of REE, we perform first-principles calculations for representative materials with different symmetries. We believe that our results will be helpful for further computational and experimental studies, as well as the design of spintronics devices., Comment: 10 pages, 5 figures

Ferroelectric materials hold great potential for alternative memories and computing, but several challenges need to be overcome before bringing the ideas to applications. In this context, the recently discovered link between electric polarization and spin textures in some classes of ferroelectrics expands the perspectives of the design of devices that could simultaneously benefit from ferroelectric and spintronic properties. Here, we explore the concept of non-volatile ferroelectric control of charge-to-spin conversion in semimetallic WTe$_2$, which may provide a way for non-destructive read-out of the polar state. Based on the first-principles simulations, we show that the Rashba-Edelstein effect (REE) that converts electric currents into spin accumulation switches its sign upon the reversal of the electric polarization. The numerical values of REE, calculated for the first time for both bulk and bilayer WTe$_2$, demonstrate that the conversion is sizable, and may remain large even at room temperature. The ferroelectric control of spin transport in non-magnetic materials provides functionalities similar to multiferroics and allows the design of memories or logic-in-memory devices that combine ferroelectric writing of information at low power with the spin-orbit read-out of state.

We report on the Fermi surfaces and superconducting parameters of CaSb$_2$ single crystals (superconducting below $T_{\text{c}}\sim 1.8~\text{K}$) grown by the self-flux method. The frequency of de-Haas-van-Alphen and Shubnikov-de-Haas oscillations evidences a quasi-two-dimensional (quasi-2D) Fermi surface, consistent with one of the Fermi surfaces forming Dirac lines predicted by first-principles calculations. Measurements in the superconducting state reveal that CaSb$_2$ is close to a type-I superconductor with the Ginzburg-Landau (GL) parameter of around unity. The temperature dependence of the upper critical field $H_{\text{c2}}$ is well described by a model considering two superconducting bands, and the enhancement of the effective mass estimated from $H_{\text{c2}}(0~\text{K})$ is consistent with the quasi-2D band observed by the quantum oscillations. Our results indicate that a quasi-2D band forming Dirac lines contributes to the superconductivity in CaSb$_2$., Comment: 13 pages, 13 figures

Chiral materials, similarly to human hands, have distinguishable right-handed and left-handed enantiomers which may behave differently in response to external stimuli. Here, we use for the first time an approach based on the density functional theory (DFT)+PAOFLOW calculations to quantitatively estimate the so-called collinear Rashba-Edelstein effect (REE) that generates spin accumulation parallel to charge current and can manifest as chirality-dependent charge-to-spin conversion in chiral crystals. Importantly, we reveal that the spin accumulation induced in the bulk by an electric current is intrinsically protected by the quasi-persistent spin helix arising from the crystal symmetries present in chiral systems with the Weyl spin-orbit coupling. In contrast to conventional REE, spin transport can be preserved over large distances, in agreement with the recent observations for some chiral materials. This allows, for example, the generation of spin currents from spin accumulation, opening novel routes for the design of solid-state spintronics devices.

Direct and inverse spin Hall effects lie at the heart of novel applications that utilize spins of electrons as information carriers, allowing generation of spin currents and detecting them via the electric voltage. In the standard arrangement, applied electric field induces transverse spin current with perpendicular spin polarization. Although conventional spin Hall effects are commonly used in spin-orbit torques or spin Hall magnetoresistance experiments, the possibilities to configure electronic devices according to specific needs are quite limited. Here, we investigate unconventional spin Hall effects that have the same origin as conventional ones, but manifest only in low-symmetry crystals where spin polarization, spin current and charge current are not enforced to be orthogonal. Based on the symmetry analysis for all 230 space groups, we have identified crystal structures that could exhibit unusual configurations of charge-to-spin conversion. The most relevant geometries have been explored in more detail; in particular, we have analyzed the collinear components yielding transverse charge and spin current with spin polarization parallel to one of them, as well as the longitudinal ones, where charge and spin currents are parallel. In addition, we have demonstrated that unconventional spin Hall effect can be induced by controllable breaking the crystal symmetries by an external electric field, which opens a perspective for external tuning of spin injection and detection by electric fields. The results have been confirmed by density functional theory calculations performed for various materials relevant for spintronics. We are convinced that our findings will stimulate further computational and experimental studies of unconventional spin Hall effects.