Layered PtBi_2 is a candidate for topological superconductivity arising in Fermi-arc surface states. Using spin- and angle-resolved photoemission spectroscopy, we demonstrate that the Fermi arcs in PtBi_2 are singly degenerate and spin-polarized, which establishes their nontrivial topology and constitutes a necessary condition for topological superconductivity. We further uncover a pronounced surface-termination dependence of the Fermi-arc dispersion, yielding either nearly flat or approximately linear bands in agreement with first-principles calculations. Together, the observed spin polarization and termination-dependent bandwidth of the Fermi-arc surface states identify key ingredients underlying the potential emergence of topological superconductivity in PtBi_2.

Pressure offers a clean, reversible tuning knob for steering competing interactions in functional quantum materials and stabilizing emergent phases. Ferromagnetic MnSb2Te4 combines the state of a magnetic topological semimetal, a high Curie temperature and a sizable net magnetic moment, making it a promising platform for the high-temperature quantum anomalous Hall effect. Yet, theory predicts ferromagnetic stoichiometric MnSb2Te4 to host Weyl nodes at the Fermi energy. Using first-principles calculations, we map the structural, electronic, topological and magnetic evolution of MnSb2Te4 under hydrostatic compression of 0−10GPa. The calculated magnetic ordering temperature decreases with increasing pressure, indicating a suppression of ferromagnetic order. Covalent and van der Waals bonds shorten under pressure while the trigonal lattice is preserved. The shorter Sb–Te bond, that drives the pz−pz topological band inversion, is the least compressible. Its slight contraction enhances orbital overlap, triggers a pressure-induced double-band inversion, and shifts the Weyl node from the Fermi level into the conduction band. This change drives a topological phase transition from a Weyl semimetal to a topological semimetal with a Z4=2 topological invariant. This new mechanism thus creates a topological phase that can be adiabatically deformed into a magnetic topological insulator or axion insulator. The non-trivial nature of the new semimetallic phase ensures that gapped Dirac cones persist at the surface, although they appear as resonances embedded in the bulk continuum. Our results highlight lattice-driven band inversions as a versatile handle for engineering topological phases in magnetic van der Waals systems.

Recent reports of surface-localized topological superconductivity in trigonal PtBi_2 highlight the importance of understanding its surface electronic structure. We investigate the bulk and surface band structure of PtBi_2 using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Through photon-energy- and polarization-dependent measurements, we disentangle bulk dispersions from surface states on the two distinct surface terminations of PtBi_2(0001). For both terminations, we assign several different surface states and find good agreement between experiment and calculations. Based on our calculations, we analyze the orbital composition in the surface and bulk bands and compare the results to polarization-dependent ARPES measurements. Together, our results provide a coherent picture of the surface electronic structure of PtBi_2 across both surface terminations.

Magnetic topological insulators can host chiral 1D edge channels at zero magnetic field, when a magnetic gap opens at the Dirac point in the band structure of 2D topological surface states, lead- ing to the quantum anomalous Hall effect in ultra-thin nanostructures. For thicker nanostructures, quantization is severely reduced by the co-existence of edge states with other quasi-particles, usually considered as bulk states. Yet, surface states also exist above the magnetic gap, but it remains difficult to identify electronic subbands by electrical measurements due to strong disorder. Here we unveil surface states in MnBi2Te4 nanostructures, using magneto-transport in very-high magnetic fields up to 55 T, giving evidence of Shubnikov-de-Haas oscillations above 40 T. A detailed analysis confirms the 2D nature of these quantum oscillations, thus establishing an alternative method to photoemission spectroscopy for the study of topological surface states in magnetic topological insulators, using Landau level spectroscopy.

Achieving efficient ultrafast optical control of antiferromagnetic spin dynamics is a central goal for next-generation high-speed THz spintronic and magnonic devices. Resonant optical pumping of crystal-field-split d-d orbital multiplets in magnetic TM ions directly modulates exchange and spin-orbit interactions, inducing large-amplitude coherent spin precession. However, such effects are limited to a handful of systems and there is no general strategy to enhance d-d photomagnetism in antiferromagnets. Here, we demonstrate the engineering of photomagnetism via TM-ion doping in collinear van der Waals antiferromagnets. In Mn_1-xNi_xPS_3, small amounts of Ni^2+ activate a strong photomagnetic response while largely preserving the Néel ground state. Even 10

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.

Intrinsic magnetic topological insulators can host quantum states with quantized magneto-electric responses, such as the axion and Chern insulators states evidenced in ultra-thin MnBi2Te4 films. Yet, whereas quantization is investigated thoroughly, transport properties related to the phase of charge carriers remains unexplored. Here, we study quantum coherent transport in mesoscopic Hall bars fabricated from thick exfoliated MnBi2Te4 flakes, and reveal the longest phase-coherence length ever observed in a mesoscopic magnet (about 500nm at 1K), associated to 2D topological surface states. In the fully-coherent regime, significant non-local contributions to quantum interference up to the micron scale lead to giant-amplitude universal conductance fluctuations (about 20e2/h). In the self-averaging regime, the statistical properties of conductance fluctuations confirm the 2D nature of quantum interference and different dephasing mechanisms are identified, as due to either magnetism or magnetic flux through coherent loops. Remarkably, the weak decoherence in magnetic topological insulator nanostructures show their potential to realize novel quantum spin interferometers based on dephasing by local magnetic textures at liquid-helium temperatures.

Layered ternary (MnX 2Te4)(X 2Te3) n (X = Bi or Sb, n = 0-3) tellurides are intensely studied as perspective magnetic topological insulators: MnBi2Te4 and MnBi4Te7 demonstrate the quantum anomalous Hall effect up to several Kelvin. To enlarge the temperature range for this quantum behavior, the materials require a net magnetization and a high Curie temperature, T C. Recently, we found that Mn enrichment and Mn/Sb site intermixing increase the T C from 30 K in MnSb2Te4 to 58 K in Mn2.01(1)Sb1.19(1)Te4. Here, we synthesize the utmost manganese-rich members of this materials family, with an average Mn content of 28-32 at. % and the record T C = 65-73 K nearing the liquid-nitrogen threshold. By combining single-crystal X-ray diffraction, ab initio modeling and bulk DC magnetization, we pinpoint the relationship between the lattice symmetry and the magnetic order. The trigonal Mn1.90(1)Sb1.39(1)Te4 phase with manganese atoms in the van der Waals gap hosts the highest-T C ferrimagnetic state. We get the first insights into its electronic structure and topological nature by ab initio modeling using density functional theory. Initiated by the filling of the van der Waals gap, the compound mimics a structural transition from a trigonal (sp. gr. R3m) to a cubic lattice (sp. gr. Fm3m), which is reminiscent of the structural polymorphism of the Ge-Sb-Te thermoelectrics.

We investigated the electronic properties of the topological insulator Bi_2Te_3 by scanning tunneling microscopy and spectroscopy at low temperature. We obtained high-resolution quasiparticle interference data of the topological surface Dirac electrons at different energies. Spin-selective joint density of states calculations were performed for surface and bulk electronic states to interpret the observed quasiparticle interference data. The topological properties of our crystals are demonstrated by the absence of backscattering along with the linear energy dispersion of the dominant scattering vector. In addition, we detect non-dispersive scattering modes which we associate with bulk-surface scattering and, thus, allow an approximate identification of the bulk energy gap range based on our quasiparticle interference data. Measurements of differential conductance maps in magnetic fields up to 15 T have been carried out, but no strong modifications could be observed.

High-resolution angle-resolved photoemission spectroscopy (ARPES) performed on the single-layered cuprate (Pb1-y,Biy)2Sr2-xLaxCuO6+delta (Bi2201) reveals a 6-10% difference in the nodal kF vectors along the TY and TX directions. This asymmetry is notably larger than the 2% orthorhombic distortion in the CuO2 plane lattice constants determined using X-ray crystallography from the same samples. First principles calculations indicate that crystal-field splitting of the bands lies at the root of the kF asymmetry. Concomitantly, the nodal Fermi velocities for the TY quadrant exceed those for TX by 4%. Momentum distribution curve widths for the two nodal dispersions are also anisotropic, showing identical energy dependencies, bar a scaling factor of similar to 1.17 +/- 0.05 between TY and TX. Consequently, the imaginary part of the self-energy is found to be 10-20% greater along TY than TX. These results emphasize the need to account for Fermi surface asymmetry in the analysis of ARPES data on Bi-based cuprate high temperature superconductors such as Bi2201. To illustrate this point, an orthorhombic tight-binding model (with twofold in-plane symmetry) was used to fit ARPES Fermi surface maps spanning all four quadrants of the Brillouin zone, and the ARPES-derived hole-doping (Luttinger count) was extracted. Comparison of the Luttinger count with one assuming four-fold in-plane symmetry strongly suggests the marked spread in previously-reported Fermi surface areas from ARPES on Bi2201 results from the differences in kF along TY and TX. Using this analysis, a new, linear relationship emerges between the hole-doping derived from ARPES (pARPES) and that derived using the Presland (pPresland) relation such that pARPES = pPresland + 0.11. The implications for this difference between the ARPES-and Presland-derived estimates for p are discussed and possible future directions to elucidate the origin of this discrepancy are presented.

Various approaches to the optical diagnostics of evolving polymer foams formed as a result of a decrease in the external pressure according to a given scenario in the "polymer-supercritical fluid" systems are considered.Formed polymer foams are considered as a material platform for the creation of scaffolds for biomedical applications. Diagnostics of the current state of the foam was carried out by statistical analysis of the spatiotemporal fluctuations of the probe laser radiation,multiple scattered in the volume of the evolving foam, or by analyzing the fluorescent response during foaming of the "polymer-fluorophore" mixture, pumped by laser radiation in the absorption band of the fluorophore. A relationship has been established between the average lifetime of dynamic speckles in scattered laser light and a generalized parameter characterizing the foam expansion dynamics. It was also found that the waveguide effect in the walls of the formed pores has a significant influence on the fluorescent response of the evolving foam, leading to an increase in the characteristic dwell time of fluorescence radiation in the walls and, accordingly, to an increase in the contribution of the induced component to the fluorescent response. Keywords: fluorescent response, speckle correlometry, polylactide, foaming, supercritical carbon dioxide.

AbstractTopological superconductors hosting Majorana zero modes are of great interest for both fundamental physics and potential quantum computing applications. In this work, we investigate the transport properties of the intrinsic magnetic topological insulator MnBi2Te4 (MBT). In normal transport measurements, we observe the presence of chiral edge channels, though with deviations from perfect quantization due to factors such as non-uniform thickness, domain structures, and the presence of quasi-helical edge states. Subsequently, we fabricate superconducting junctions using niobium leads on MBT exfoliated flakes, which show an onset of supercurrent with clear Josephson coupling. The interference patterns in the superconducting junctions reveal interesting asymmetries, suggesting changes in the magnetic ordering of the MBT flakes under small applied magnetic fields. Moreover, the modulation of the critical current by magnetic field reveals a SQUID-like pattern, suggesting the presence of supercurrent through the quasi-helical edge states.

Magnetic topological insulators (TIs) herald a wealth of applications in spin-based technologies, relying on the novel quantum phenomena provided by their topological properties. Particularly promising is the (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ layered family of established intrinsic magnetic TIs that can flexibly realize various magnetic orders and topological states. High tunability of this material platform is enabled by manganese-pnictogen intermixing, whose amounts and distribution patterns are controlled by synthetic conditions. Positive implication of the strong intermixing in MnSb$_2$Te$_4$ is the interlayer exchange coupling switching from antiferromagnetic to ferromagnetic, and the increasing magnetic critical temperature. On the other side, intermixing also implies atomic disorder which may be detrimental for applications. Here, we employ nuclear magnetic resonance and muon spin spectroscopy, sensitive local probe techniques, to scrutinize the impact of the intermixing on the magnetic properties of (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ and MnSb$_2$Te$_4$. Our measurements not only confirm the opposite alignment between the Mn magnetic moments on native sites and antisites in the ground state of MnSb$_2$Te$_4$, but for the first time directly show the same alignment in (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ with n = 0, 1 and 2. Moreover, for all compounds, we find the static magnetic moment of the Mn antisite sublattice to disappear well below the intrinsic magnetic transition temperature, leaving a homogeneous magnetic structure undisturbed by the intermixing. Our findings provide a microscopic understanding of the crucial role played by Mn-Bi intermixing in (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ and offer pathways to optimizing the magnetic gap in its surface states.

AbstractMagnetic topological insulators (TIs) herald a wealth of applications in spin‐based technologies, relying on the novel quantum phenomena provided by their topological properties. Particularly promising is the (MnBi2Te4)(Bi2Te3)n layered family of established intrinsic magnetic TIs that can flexibly realize various magnetic orders and topological states. High tunability of this material platform is enabled by manganese–pnictogen intermixing, whose amounts and distribution patterns are controlled by synthetic conditions. Here, nuclear magnetic resonance and muon spin spectroscopy, sensitive local probe techniques, are employed to scrutinize the impact of the intermixing on the magnetic properties of (MnBi2Te4)(Bi2Te3)n and MnSb2Te4. The measurements not only confirm the opposite alignment between the Mn magnetic moments on native sites and antisites in the ground state of MnSb2Te4, but for the first time directly show the same alignment in (MnBi2Te4)(Bi2Te3)n with n = 0, 1 and 2. Moreover, for all compounds, the static magnetic moment of the Mn antisite sublattice is found to disappear well below the intrinsic magnetic transition temperature, leaving a homogeneous magnetic structure undisturbed by the intermixing. The findings provide a microscopic understanding of the crucial role played by Mn–Bi intermixing in (MnBi2Te4)(Bi2Te3)n and offer pathways to optimizing the magnetic gap in its surface states.

AbstractThe layered material α-RuCl3 is a promising candidate to realize the Kitaev quantum spin liquid (QSL) state. However, at ambient pressure, deviations from the perfect Kitaev geometry prevent the existence of the QSL state at low temperatures. Here we present the discovery of a pressure-induced high-symmetry phase in α-RuCl3, which creates close to ideal conditions for the emergence of a QSL. Employing a novel approach based on Bragg and diffuse scattering of synchrotron radiation, we reveal a pressure-induced reorganization of the RuCl3-layers. Most importantly, this reorganization affects the structure of the layers themselves, which acquire a high trigonal symmetry. For this trigonal phase the largest ratio between the Kitaev (K) and the Heisenberg exchange (J) ever encountered is found: K/J = 124. Additionally, we demonstrate that this phase can also be stabilized by a slight biaxial pressure. This not only resolves the conflicting reports of low-temperature structures in the literature, but also facilitates the investigation of the high-symmetry phase and its potential QSL using a range of experimental techniques.

The van-der-Waals antiferromagnetic topological insulator MnBi2Te4 is one of the few materials that realize the sought-after quantum anomalous Hall (QAH) state and quantized surface charge transport. To assess the relevance of its isostructural analog MnSb2Te4 as a potential QAH candidate, the roles of Mn/Sb site mixing and cationic vacancies need to be clarified. Recent findings have shown that non-stoichiometry in Mn1 +/- xSb2 -/+ xTe4 is an efficient tuning knob to achieve a net spin-polarized state and to raise the magnetic ordering temperature well above that of MnBi2Te4. Here, we report the crystal structure, the bulk and the surface magnetism of two new Mn1+xSb2_xTe4 samples: Mn1.08Sb1.92Te4(x approximate to 0.1) with TC = 44 K, and Mn2.01Sb1.19Te4(x approximate to 1.0) with the record TC = 58 K. We quantify the site mixing comprehensively by combining various structural probes on powders and single crystals, and then employ bulk, local (electron spin resonance), and spectroscopic (x-ray magnetic circular dichroism) probes to connect these insights to the magnetism of these materials. We demonstrate that Mn over-stoichiometry up to x = 1.0, in combination with a particular Mn/Sb intermixing pattern and the increasingly three-dimensional character of the magnetic order, push the TC upwards. The tendency towards more robust ferromagnetism mediated by stronger interlayer exchange in Mn1+xSb2_xTe4 upon increasing x is confirmed by bulk magnetometry and by a series of density-functional-theory calculations of model structures with varying intermixing.

Utilizing an interplay between band topology and intrinsic magnetism, the two-dimensional van der Waals (vdW) system MnBi_2Te_4 provides an ideal platform for realizing exotic quantum phenomena and offers great opportunities in the emerging field of antiferromagnetic spintronic technology. Yet, the fabrication of MnBi_2Te_4-based nanodevices is hindered by the high sensitivity of this material, which quickly degrades when exposed to air or to elevated temperatures. Here, we demonstrate an alternative route of fabricating vdW-MnBi_2Te_4-based electronic devices using the cryogenic dry transfer of a printable circuit embedded in an inorganic silicon nitride membrane. The electrical connections between the thin crystal and the top surface of the membrane are established through via contacts. Our magnetotransport study reveals that this innovative via contact approach enables exploring the MnBi_2Te_4-like sensitive 2D materials and engineering synthetic heterostructures as well as complex circuits based on the two-dimensional vdW systems.

The problem of rehabilitation of patients with multimorbid pathology currently holds its medical and social relevance, due to the complexity of choosing an adequate treatment and predicting possible complications at the hospital stage. This is determined by the predominant monomorbid nature of clinical recommendations, as well as the difficulty of analyzing all risk factors and predicting the outcome of a comorbid disease. The article describes the case of a 60-year-old man with comorbid cerebrocardiovascular pathology, transferred from the palliative department to a rehabilitation center. The score on the Rehabilitation Routing Scale (RRS) was 5 points with a prospective regression to 6 points. As part of a multidisciplinary rehabilitation team (MDRT), the patient underwent a complex of rehabilitation measures including physical and cognitive rehabilitation, apparatus physiotherapy, speech and occupational therapy, complementary to medication. On the 21st day of rehabilitation measures, the patient's condition improved by 1.2 times in terms of RRS, 4 times according to the NIHSS stroke scale, 3 times in muscle strength according to the MRCWS, 2 times in mAS spasticity, 4 times in dysphagia, and 1,5 times in balance, Barthel Index of ADL – by 1.5 times, Rivermead Mobility Index – 3 times.

Nanoscale phase separation was induced in the K‐doped RuCl 3 van der Waals material by annealing, and studied with the goal to find a natural design strategy for the formation of two‐dimensional architectures as an alternative to the costly and time‐consuming experimental artificial growth methods. Phase conversion was traced by means of thermogravimetric analysis combined with mass spectrometry. The local crystal structure of co‐existing K 3 Ru 2 Cl 9 domains with the sizes of about 100 nm was solved by 3D electron diffraction.