Dirac band crossing and topological surface states are crucial for verifying and exploring topological materials. As an isostructural heavy fermion Ce-115 compound, ${\mathrm{LaRhIn}}_5$ exhibits exotic transport behavior potentially arising from linear crossing, although experimental evidence is still lacking. Here, by using angle-resolved photoemission spectroscopy and density functional theory calculations, we reveal the existence of a three-dimensional Dirac point protected by $C_4$ symmetry in ${\mathrm{LaRhIn}}_5$. Moreover, surface states merging into the bulk Dirac bands are also observed, akin to most topological semimetals. However, a comprehensive calculation of the system's topological index indicates a trivial $Z_2$ invariant, which excludes the existence of strong topological nature in the system. The existence of the three-dimensional Dirac fermion in ${\mathrm{LaRhIn}}_5$ might contribute to the understanding of the electronic structure in ${\mathrm{LaRhIn}}_5$ and shed light on the topological nature of the isostructural Ce-115 system.

In this contribution, by employing first-principles calculations and nonadiabatic molecular dynamic simulations, we unequivocally substantiate that the ternary graphene/$\mathrm{ZrA}{\mathrm{s}}_2/\mathrm{HfA}{\mathrm{s}}_2$ van der Walls heterojunction is a highly promising photocatalyst for water splitting. First, through the investigation of stabilities, electronic structures, and optical absorption of two-dimensional $M{X}_2$ series ($M$ = Ti, Zr, Hf; $X$ = N, P, As), $\mathrm{ZrA}{\mathrm{s}}_2/\mathrm{HfA}{\mathrm{s}}_2$ heterojunction was screened out, which features a type-II staggered band arrangement with a Z-type charge transfer mode. Due to the inert activity of intrinsic $\mathrm{ZrA}{\mathrm{s}}_2/\mathrm{HfA}{\mathrm{s}}_2$, the inclusion of external potential still failed to trigger a hydrogen evolution reaction (HER). Second, to boost the photocatalytic activity, graphene was attached to the binary heterostructure. Due to the lower work function of graphene, the energy bands of the ternary graphene/$\mathrm{ZrA}{\mathrm{s}}_2/\mathrm{HfA}{\mathrm{s}}_2$ heterojunction were elevated as a whole, leading to a spontaneous HER. Meanwhile, the built-in electric field was enhanced. The enhanced electric field, on one hand, increases the barrier at the $\mathrm{ZrA}{\mathrm{s}}_2/\mathrm{HfA}{\mathrm{s}}_2$ interface, leading to a longer residence time for the more energetic electrons and holes; and on the other hand, the formation of ohmic contact causes a barrierless transfer for the charges at the graphene/$\mathrm{ZrA}{\mathrm{s}}_2$ interface, and the accumulated electrons rapidly recombine with the holes via the interlayer channel in the effect of enhanced electric field. Moreover, the ternary heterojunction exhibits excellent light absorption characteristics in the visible spectrum, accompanied by a predicted high light conversion efficiency. Our results not only offer a strategy for the photocatalytic performance to be enhanced by attaching graphene to a binary heterostructure but also propose a solid photocatalytic mechanism for the enhanced activity.

The semimetallic to semiconductor transition of a complex oxide, ${\mathrm{Mo}}_8{\mathrm{O}}_{23}$, remains a mysterious process among low-dimensional conductors. Although a general agreement was reached that the transition originates from a purely structural tilt instability related to the ${\mathrm{M}}_3$ instability of perovskites, recent scanning tunneling microscopy as well as Raman/IR reflectivity measurements have cast doubt about this scenario. We report an in-depth analysis of the density functional theory electron-hole response of this material, showing that a consistent scenario for the evolution of its structural and physical properties can not be put forward without taking into account an electron-hole instability at $\mathrm{\Gamma }$ of the perovskite fragment of the structure. We propose that the mechanism of the semimetallic to semiconductor transition involves several order parameters: (i) an octahedral tilt instability (${\eta }_{\text{tilt}}$) driving the incommensurate and later commensurate modulations, and (ii) a $\mathrm{\Gamma }$ electron-hole instability coupled with the lattice via a low-frequency Raman mode. The latter induces the uniform deformation (i.e., tetramerization) of a group of four corner-sharing ${\mathrm{MoO}}_6$ octahedra (${\eta }_{\text{unif}}$) repeating along one of the directions of the lattice. The two order parameters are of different symmetries and are independent in the semimetallic state but couple when the inversion symmetry is lost in the semiconducting state and the Raman mode becomes polar. The development of the uniform order of octahedral tetramers competes with the electronic and structural degrees of freedom of the high-temperature staggered tilt wave and induces a disorder of tetramer orientations stopping the growth of the charge density wave (CDW) coherence below 200 K. It is proposed that the generated polar orientation disorder can be explained by the formation of a series of solitons and antisolitons in the CDW, evidenced by a strong optical response.

We construct a protocol to adiabatically prepare the ground state of a widely discussed number-conserving model Hamiltonian for ultracold atoms in optical lattices that supports Majorana edge states. In particular, we introduce a symmetry breaking mass term that amounts to threading a commensurate (artificial) magnetic flux through the plaquettes of the considered two-leg ladder, which opens a constant bulk gap. This enables the preparation of the topological Majorana phase from a trivial Mott insulator state with optimal asymptotic scaling of the ramp time in system size, which is linear owing to the critical nature of the target state. Using constructive bosonization techniques that account for both finite-size effects and global fermion number conservation, we are able to fully explain with theory the somewhat counterintuitive necessity of the aforementioned commensurate flux for a controlled bulk gap. Our analytical predictions are corroborated and quantified by unbiased numerical matrix product state (MPS) simulations. Directly building on previous experimental work, the crucial flux-term of the proposed protocol is feasible with state-of-the-art experimental techniques in atomic quantum simulators.

This work presents a first-principles study of the (001) surface energetics of nine $AB{\mathrm{O}}_3$ perovskites ($A=\mathrm{Ca},\mathrm{Sr},\mathrm{Ba}$; $B=\mathrm{Ti},\mathrm{Zr},\mathrm{Sn}$), with a focus on the role of surface vacancies in determining termination stability. Additionally, investigation into the behavior of vacancies as a function of depth from the surface in these perovskites is carried out, and results are compared to formation of the vacancies in bulk. Combining results from these investigations reveals a general trend for all nine perovskites: the undefected $A\mathrm{O}$ surface is more energetically favorable to form than the $B{\mathrm{O}}_2$ surface. This dominance of the $A\mathrm{O}$ over the $B{\mathrm{O}}_2$ surface is further enforced by the phase diagrams of perovskite surfaces. However, $A$-site vacancies at the $A\mathrm{O}$ surface are far more favorable ($1–2 \mathrm{e}\mathrm{V}$ lower in energy) than $B$-site vacancies at the $B{\mathrm{O}}_2$ surface. Charged vacancies only drive this further under oxygen-rich conditions, showing a smaller range of stability for the $A\mathrm{O}$ than the $B{\mathrm{O}}_2$ surface. These results indicate that, while the $A\mathrm{O}$ surface is easier to form, the $B{\mathrm{O}}_2$ surface will display better long-term stability, making it more suitable for use in potential applications. This study furthers the understanding of oxide perovskite (001)-terminated surface stability, which will aid in surface growth and manufacturing.

Terahertz scanning near-field optical microscope (THz-SNOM) is employed to measure ultrafast evolution of terahertz conductivity spectra after photoexcitation of GaAs and InP wafers using ultrashort laser pulses. Unlike in GaAs, the terahertz photoconductivity decay in InP is controlled mainly by the diffusion of electrons away from the photoexcited area, and by the drift due to band bending at the surface of the semiconductor. We propose and discuss several general strategies of the analysis of signals measured using THz-SNOM, and we estimate the accuracy of the obtained near-field photoconductivity spectra.

Optically active defects suspended in an inert solid are an interesting system for sensing and magnetometry at the nanometer scale, in addition to being a potential source of high-density, identical quantum emitters for quantum information. Beyond their response to external fields, the optical absorption and emission spectra also reflect information about the host matrix, which is critical to understand for either application. For the particular system of thulium atoms implanted in solid argon, high resolution laser spectroscopy reveals narrow ensemble linewidths of the $1140\mathrm{n}\mathrm{m}$ $f$ to $f$ ground state spin-orbit transition, which is split due to crystal field effects and hyperfine coupling. Pump-probe spectroscopy is used to identify crystal field levels in at least two stable trapping sites, and the crystal field is determined to be nearly axial in both sites. Strong selection rules indicate that this transition becomes magnetic-electric in the argon host, most likely due to dielectric effects. In the presence of $\mathrm{m}\mathrm{T}$ magnetic fields, Zeeman shifts are resolvable by laser fluorescence, allowing crystal axis selective polarized spectroscopy. These results show that all-optical detection schemes for DC magnetic fields are already possible with thulium-doped argon, and point towards more informed strategies for monitoring and improving crystal growth and annealing.

In this article, dielectric nonlinearities in $0.5\left({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{TiO}}_3\right)-0.5\left({\mathrm{BaZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3\right)$ thin film are studied using impedance spectroscopy and harmonic measurements, as a function of the AC measuring field, at different frequencies and upon cycling. The measurements reveal that the pinching of the hysteresis loop, characterized by a phase angle of the third harmonic close to $-270deg$, is stronger for low frequencies. This confirms that the pinching is induced by the presence of polar nanoregions (PNRs), whose responses are also strongly dependent on frequency. When repeating the measurement, the PNR contribution changes since the phase angle of the third-harmonic response evolves from pinched to conventional relaxor. This shows that strong changes in the PNR configuration can be induced, even for low AC fields. First-order reversal curves (FORCs) confirm the presence of a pinched hysteresis loop. When repeating the FORC measurement a second time, the distribution drastically changes and corresponds to a soft ferroelectric. The asymmetry of the Preisach plane measured using FORCs is confirmed by a proposed measurement strategy: unipolar impedance measurements.

The one-dimensional tilted, periodically driven Fermi-Hubbard chain is a paradigm in the study of quantum many-body physics, particularly for solid-state systems. We uncover the emergence of Floquet scarring states, a class of quantum many-body scarring (QMBS) states that defy random thermalization. The underlying physical mechanism is identified to be the Floquet resonances between these degenerate Fock bases that can be connected by one hopping process. It is the first-order hopping perturbation effect. Utilizing the degenerate Floquet perturbation theory, we derive the exact conditions under which the exotic QMBS states emerge. Phenomena such as quantum revivals and subharmonic responses are also studied. Those results open the possibility of modulating and engineering solid-state quantum many-body systems to achieve nonergodicity.

Motivated by recent theoretical and experimental interest in metamaterials comprising nonlocal coupling terms, we present an analytic framework to realize materials with arbitrary complex dispersion relations. Building on the inverse design method proposed by Kazemi et al. [Phys. Rev. Lett. 131, 176101 (2023)], which demonstrated arbitrary real dispersion relations with real nonlocal coupling terms, we show that using nonconservative, nonlocal couplings not only can band structures be drawn, but arbitrary attenuation of the supported modes can be achieved by tuning their trajectory in the complex frequency plane. This is demonstrated using a canonical mass-spring lattice with higher-order spatial connections; we consider the energy velocity in such systems and show that competing loss and gain of the complex interactions can produce exotic wave dispersion.

${\mathrm{ZrW}}_2{\mathrm{O}}_8$ is the prototypical example of a material exhibiting negative thermal expansion (NTE). It is now widely accepted that in ${\mathrm{ZrW}}_2{\mathrm{O}}_8$, and in many other framework materials exhibiting NTE, a collection of low energy phonon modes, as opposed to just one or two, are responsible for the anomalous thermal properties. However, quantitative verification and analysis of the density functional theory (DFT) calculations which underpin this proposal are still lacking. In particular, probing the low energy phonons directly throughout reciprocal space using inelastic neutron scattering, as opposed to other techniques which only probe the Brillouin zone center, is technically challenging and hence rarely done. Here we report inelastic neutron scattering measurements in a large number of Brillouin zones over a 400 K temperature range. We find excellent agreement between DFT calculations and experimental data at low temperature. However, the shifts in phonon modes predicted by DFT due to the reduction in lattice parameter (warming) are not observed. This is most likely due to counteractive anharmonic effects, which we verified using finite temperature molecular dynamics (MD) calculations. Notwithstanding, both DFT and MD results are consistent with NTE in ${\mathrm{ZrW}}_2{\mathrm{O}}_8$ arising from the tension effect, and by extension this explanation is supported by the neutron scattering results.

The quantum adiabatic theorem is a fundamental result in quantum mechanics, with a multitude of applications, both theoretical and practical. Here, we investigate the dynamics of adiabatic processes for quantum many-body systems by analyzing the properties of observable-free intensive quantities. In particular, we study the adiabatic rate function $f(T,\mathrm{\Delta }\lambda )$ in dependence of the ramp time $T$, which gives us a complete characterization of the many-body adiabatic fidelity as a function of $T$ and the strength of the parameter displacement $\mathrm{\Delta }\lambda$. $f(T,\mathrm{\Delta }\lambda )$ quantifies the deviation from adiabaticity for a given process and therefore allows us to control and define the notion of adiabaticity in many-body systems. First we study $f(T,\mathrm{\Delta }\lambda )$ for the one-dimensional transverse field Ising model and the Luttinger liquid, both of which are quadratic systems and therefore allow us to look at the thermodynamic limit. For ramps across gapped phases, we relate $f(T,\mathrm{\Delta }\lambda )$ to the transition probability of the system and for ramps across a gapless point, or gapless phase we relate it to the excitation density of the relevant quasiparticles. Then we investigate the XXZ model, which allows us to see the qualitative features that survive when interactions are turned on. Several key results in the literature regarding the interplay of the thermodynamic and the adiabatic limit are obtained as inferences from the properties of $f(T,\mathrm{\Delta }\lambda )$ in the large-$T$ limit.

We present a multiscale computational approach that combines atomistic spin models with the cluster multipole (CMP) method. The CMP method enables a systematic and accurate generation of complex noncollinear magnetic structures using symmetry-adapted representations. The parameters of the spin model are derived from density functional theory using the magnetic force theorem, with the paramagnetic state as a reference. The energy landscape of CMP-generated structures is inspected at the model Hamiltonian level and sets of low-energy magnetic structures are identified for each material candidate. The inclusion of relativistic antisymmetric and anisotropic pair interactions lifts partially the degeneracy among these most stable structures. To demonstrate the applicability and predictive capability of the method, we apply it to the noncollinear ${\mathrm{Mn}}_{3}X$ and collinear ${\mathrm{Fe}}_{3}X$ $(X=\mathrm{Ga},\mathrm{Ge}, \text{and} \mathrm{Sn})$ kagome compounds. The computational efficiency of the method in identifying low-energy structures among multiple CMP configurations highlights its potential for high-throughput screening of complex magnets with unknown magnetic order.

The hexagonal ${\mathrm{Mn}}_{3-x}{\mathrm{Fe}}_x\mathrm{Sn}$ compounds possess several desirable properties that make them suitable magnetocaloric materials, including a ferromagnetic (FM)-to-paramagnetic (PM) transition near room temperature and soft magnetic behavior. In this study, we use the melt-spinning technique to explore the Mn-Fe-Sn ternary system. By combining magnetization measurements, Mössbauer spectroscopy, neutron diffraction (ND), oriented powder x-ray diffraction, and density functional theory (DFT) calculation, the magnetocaloric effect, spin structures, and the intrinsic magnetic properties of polycrystalline ${\mathrm{Mn}}_{3-x}{\mathrm{Fe}}_x\mathrm{Sn}$ $(x=0.8-1.4)$ compounds are determined. The FM-to-PM transition temperature $T_{\mathrm{C}}$ ranges from 253 K $(x=0.8)$ to 394 K $(x=1.4)$. At low temperature, a spin reorientation at $T_{\mathrm{S}}$ is observed, where below $T_{\mathrm{S}}$ a coexistence of FM order with spins along the $c$ axis and antiferromagnetic order with spins within the $a-b$ plane occurs for $x=0.8$ and 1.0. However, for compounds with $x=1.2$ and 1.4, only FM order with spins along the $c$ axis has been found below $T_{\mathrm{S}}$. Above $T_{\mathrm{S}}$, the spin structure corresponds to FM order with spins aligned within the $a-b$ plane for all compositions. The magnetic moments of Mn and Fe were evaluated using DFT, demonstrating good agreement with the ND results.

The emergence of an orbital angular momentum (OAM) response to a charge current holds promise for technological applications, allowing electrical control of magnetization dynamics. Often, the OAM current is invoked in explaining experimental results for very large orbital transport effects, but this is conceptually challenging as the OAM current is not a conserved quantity. Instead of utilizing the orbital conductivity associated with the nonconserved OAM current, we here use nonequilibrium Green's functions to directly image the OAM density in real space under an applied electric current bias. We find strong spatial variations in OAM density, with the lattice acting as a source and sink of OAM. Moreover, we show that the OAM response depends sensitively on the angle between the charge current and the crystal axis. This enables the generation of a transverse OAM response in one current direction and solely a longitudinal response in another. We refer to this as an orbital splitter effect, analogous to the spin splitter effect in altermagnets.

Antiferromagnets are emerging as promising alternatives to ferromagnets in spintronics applications. A key feature of antiferromagnets is their anisotropic magnetoresistance (AMR), which has the potential to serve as a sensitive marker for the antiferromagnetic order parameter. However, the underlying origins of this behavior remains poorly understood, particularly in thin film geometries. In this study, we report the observation of AMR in epitaxial thin films of the collinear ${L1}_0$ antiferromagnet ${\mathrm{MnPt}}_x{\mathrm{Pd}}_{1-x}$. In the thicker films, AMR is dominated by a noncrystalline twofold component, which emerges from domain reconfiguration and spin canting under applied magnetic field. As the film thickness is reduced, however, a crystalline fourfold component emerges, accompanied by the appearance of uncompensated magnetic moment, which strongly modifies the magnetotransport properties in the thinner films. We demonstrate that interfacial interactions lead to a large density of states (DOS) at the Fermi level. This enhanced DOS, combined with disorder in the thinner films, stabilizes the uncompensated moment and results in a fourfold modulation of the DOS as the Néel vector rotates, explaining the observed AMR behavior.

Spin-orbit torque (SOT) induced magnetization switching has attracted attention because of its applicability to a fast writing method in nonvolatile memory. However, it has been clarified that the magnetization switching is sensitive to the current density, the magnetic field strength, and the initial condition, even at zero temperature due to back switching, where the magnetization moves close to the switched state in the presence of SOT but is back to the initial state after turning off the current. Here, we study the SOT-driven magnetization switching probability at finite temperature through numerical simulation of the Landau-Lifshitz-Gilbert equation. The switching probability decreases as the electric current density increases, which is in contrast to that found in the conventional spin-transfer torque devices. The decrease of the switching probability originates from the combination of the back switching and thermal fluctuation. It is found that the switching probability can be kept high when fieldlike torque with an appropriate value is introduced. The analysis on the temporal dynamics indicates that the presence of the fieldlike torque leads to an effective enhancement of the damping torque and results in a fast relaxation to the switched state, which helps to avoid the back switching.

We report the discovery of pressure-induced superconductivity transitions in RbMgBi, a nonmetallic layered compound under ambient conditions. Upon compression, RbMgBi first undergoes an insulator-to-metal transition at $\sim 4.5\mathrm{GPa}$, coinciding with the emergence of a superconducting phase (SC-I). A second superconducting phase (SC-II) appears near 10.4 GPa, with both phases coexisting until SC-II becomes dominant above $\sim 14\mathrm{GPa}$. High-pressure ac susceptibility confirmed the bulk superconducting nature in both phases. High-pressure x-ray diffraction reveals a substantial $c$-axis contraction and a structural transition from a tetragonal $P4$/nmm to an orthorhombic Cmcm phase near 5.5 GPa, underscoring the role of interlayer spacing in enabling superconductivity. Hall measurements show marked carrier evolution at the critical pressures, while first-principles calculations indicate a pressure-driven electronic reconstruction—from a single-band regime to a multiband state with enhanced Fermi velocity and superfluid density. Our results demonstrate a strong interplay between structural compression, carrier dynamics, and superconducting behavior, offering new insight into pressure-tuned superconductivity and guiding principles for designing emergent superconductors via coupled structural-electronic engineering.