The two-dimensional Shastry-Sutherland lattice (SSL) belongs to important models in the field of quantum magnetism as it combines low-dimensionality, geometrical frustration, and strong anisotropy. Besides the insulating ${\mathrm{SrCu}}_2{\left({\mathrm{BO}}_3\right)}_2$, the metallic tetraboride ${\mathrm{TmB}}_4$ belongs to its best-known examples. In this work, we investigate the development of ${\mathrm{TmB}}_4$ magnetization under magnetic fields ($B$) up to 60 T, applied at different angles with respect to the easy magnetization axis $c$. We aim to determine the extent to which phenomena associated with the SSL remain robust in high magnetic fields when the field is tilted away from this direction. Our results show that at temperatures ($T$) below 20 K, significant deviations from the easy-axis interpretation of magnetization, in which the magnetic moments of Tm-ions are oriented only parallel to $c$ axis, occur at deflection angles higher than 70° and in magnetic fields above ∼30 T. These values noticeably affect the corresponding $B$ versus $T$ phase diagram of ${\mathrm{TmB}}_4$ and point to a collapse of SSL phenomena under these conditions. The observed high field magnetization anomalies in ${\mathrm{TmB}}_4$ may also suggest the existence of new field-induced quantum phases in this Shastry-Sutherland compound.

The polymorphic rhodium-bismuth compound ${\mathrm{RhBi}}_2$ has attracted interest owing to its nontrivial topological electronic states. We report the growth of single crystals of both $\alpha$- and $\beta \text{−}{\mathrm{RhBi}}_2$ and a study of their physical properties at low temperatures and ambient and high pressures beyond 40 GPa. At ambient pressure, $\beta \text{−}{\mathrm{RhBi}}_2$ is a metal with a low density of states at the Fermi level, whereas $\alpha \text{−}{\mathrm{RhBi}}_2$ is a semimetal with large magnetoresistance ($\sim 500\%$). Point-contact Andreev-reflection spectroscopy demonstrates induced superconductivity for both phases. By applying pressure, we observe the emergence of superconductivity at $p\approx 8$ GPa in $\beta \text{−}{\mathrm{RhBi}}_2$ and at $p\approx 20$ GPa in $\alpha \text{−}{\mathrm{RhBi}}_2$, with the critical temperature $T_{\mathrm{c}}$ exhibiting a dome-shaped dependence on pressure in both phases. The maximum values of $T_{\mathrm{c}}$ are 6.6 K at $p\approx 13$ GPa for $\beta \text{−}{\mathrm{RhBi}}_2$ and 3.7 K at $p\approx 24.2$ GPa for $\alpha \text{−}{\mathrm{RhBi}}_2$. Synchrotron x-ray diffraction studies show that the crystal structure of $\alpha \text{−}{\mathrm{RhBi}}_2$ remains stable over the entire investigated pressure range. In contrast, $\beta \text{−}{\mathrm{RhBi}}_2$ undergoes a transition from a triclinic to a tetragonal structure ($\gamma \text{−}{\mathrm{RhBi}}_2$) at $p\approx 13.5$ GPa, accompanied by the attainment of the maximum value of $T_{\mathrm{c}}$.

We synthesize high-quality $\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{Z}{\mathrm{n}}_x\mathrm{Se}$ single crystals over a broad Zn-doping range ($x=0–0.023$) and systematically study the superconductivity of those single crystals. Accompanying the monotonic increment of Zn-doping concentration from 0.000 to 0.023, the superconducting transition temperature ($T_{\mathrm{c}}$) exhibits a pronounced nonmonotonic evolution, suggesting that the underlying mechanism governing $T_{\mathrm{c}}$ extends beyond simple impurity pair breaking. Magnetization and transport measurements confirm the bulk behavior of superconductivity and reveal enhanced scattering effects with Zn doping. The low-temperature specific-heat characteristic is consistently described by a two-gap multiband scenario composed of an isotropic $s$-wave gap and an anisotropic extended $s$-wave gap, whereas single-gap and alternative pairing symmetries fail to describe the data. The nearly unchanged relative weights of the two gap components are consistent with relatively weak interband scattering induced by Zn substitution, thereby preserving multiband superconductivity. These results demonstrate the robustness of multigap superconductivity in $\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{Z}{\mathrm{n}}_x\mathrm{Se}$ and impose stringent constraints on candidate pairing mechanisms, highlighting the role of multiband electronic structure and anisotropic gap formation.

We study the geometric contribution to the superfluidity in quasicrystals in which the conventional momentum-space quantum geometric tensor cannot be defined due to the lack of translational invariance. Based on the correspondence between the momentum and magnetic flux, we propose a general framework to define the quantum metric in flux space and reveal its contribution to the superfluid weight in quasicrystalline superconductors. As an application, we investigate the attractive Hubbard model on various extrinsic and intrinsic quasicrystals with flat-energy spectra. In the weak-coupling limit, we reveal the geometric origin of the superfluid weight in quasicrystals with flat-energy spectra and establish its connection to the quantum metric in flux-space. Moreover, by analyzing the spread of Wannier functions, we propose a general fluctuation mechanism that explains how quasiperiodicity modulates the integrated flux-space quantum metric. Our theory provides a general way to examine the effect of the quantum geometry in systems lacking translational symmetry.

We report intriguing characteristics of light-induced and tunable shift currents in $\mathrm{B}{\mathrm{i}}_{1-\mathrm{x}}\mathrm{S}{\mathrm{m}}_{\mathrm{x}}\mathrm{Fe}{\mathrm{O}}_3\left(0.00\le \mathrm{x}\le 0.18\right)$ films, reflecting contributions from optoelectronic processes through structural phase evolution. Optical reflectance spectroscopy reveals asymmetry in sub-band-gap and direct-band-gap transitions, indicating phase-induced energy-level shifts. We demonstrate how visible light dramatically alters transitions involving $\mathrm{O}\text{−}2p\leftrightarrow \mathrm{Fe}-3d$ exchange interactions, and how continuous-wave illumination selectively excites charge carriers in ${\mathrm{Bi}}_{1-x}{\mathrm{Sm}}_x{\mathrm{FeO}}_3$, leading to spatial separation into localized and bandlike states upon optical transitions, thereby laying out all spatial control routes to shift photovoltaic currents.

We investigate the extended $t\text{−}J$ model on honeycomb lattices with next-nearest-neighbor electron hopping $t^{\prime }$ and superexchange coupling $J^{\prime }={(t^{\prime }/t)}^{2}J$ using large-scale density-matrix renormalization group (DMRG) simulations and slave-boson mean-field theory (SBMFT). By systematically varying $t^{\prime }$ and cylinder geometries, our DMRG results reveal several competing phases with distinct charge and superconducting (SC) properties. On YC4-0 cylinders possessing bonds lying along the ${\vec{e}}_y$ direction, the ground state of doped models exhibits pronounced quasi-long-range $d$-wave SC with coexisting armchair-oriented stripes across a broad range of $t^{\prime }$. Notably, the SC Luttinger exponent has a nonmonotonic dependence on $t^{\prime }$, showing the strongest pairing tendency near $t_{\text{op}}^{\prime }\approx 0.4$ among the doping levels and parameter values studied. Conversely, XC cylinders host a competing long-range zigzag-stripe phase with exponentially decaying SC correlations for $t^{\prime }>0.5$, highlighting the role of boundary geometry in stabilizing distinct competing phases in DMRG. Complementary SBMFT calculations compare the relative energies of the competing charge patterns without finite-cylinder constraints and find the armchair stripe to have the lowest energy among the selected charge-density-wave candidates.

There are conflicting predictions and reports on the character of the exciton Mott transition (EMT) in monolayer transition metal dichalcogenides. It could be either a discontinuous or a continuous transition from the excitonic to the plasma phase, with important implications for devices such as photoswitches. To resolve the nature of the transition in monolayer ${\mathrm{WS}}_2$, we study its ultrafast optical response upon resonant photoexcitation of the A exciton across a broad range of photoexcitation densities. In agreement with previously reported measurements, we observe that the A exciton quenches gradually with increasing excitation density. However, a detailed lineshape analysis unveils an abrupt red shift in the transient peak positions of the A and B exciton resonances above an excitation density threshold. This is attributed to band gap renormalization arising from the formation of a free charge carrier plasma, i.e., the EMT. The plasma phase decays with a time constant of 0.65 ps into the excitonic state. The abrupt appearance of the plasma phase at the threshold density suggests that the EMT is a discontinuous and not a continuous transition. This work demonstrates how transient optical spectroscopy combined with simultaneous lineshape analysis of two excitonic resonances can be used to investigate the EMT in 2D materials.

To fulfill the security requirements of quantum cryptography, photon number coherence (PNC) of single-photon sources has recently become an important figure of merit. Quantum dots (QDs) embedded in photonic microcavities offer a mature source of single photons, of which many properties can be tuned by the use of different excitation protocols or parameters. We show that the “Swing-UP of quantum EmitteR population” (SUPER) scheme can significantly decrease the PNC of the emitted photon, compared to resonant excitation. The reason for this is a laser-induced Stark shift, which effectively decouples the QD from the cavity during the SUPER excitation. Our calculations account for environmental effects such as phonons and radiative losses.

By placing a thin Si layer (less than $100\mathrm{nm}$) on top of a dielectric layer over bulk Si, the optical field at a graphene/silicon Schottky junction can be enhanced by a factor of 8.4 at the wavelength of $700\mathrm{nm}$. The large field enhancement originates from the subnanometer thickness of graphene. The open-cavity structure can be tuned to enhance absorption in the near-infrared region which increases the photocurrent. Model calculations show that although the presence of a thin Si layer reduces the overall photocurrent output, the amount of silicon required to generate a given photocurrent is significantly lower than in conventional silicon solar cells. First experimental devices using graphene on silicon-on-insulator substrates have shown promising initial results.

We investigate the robustness of unbound states in one-dimensional quasiperiodic models with very deep potentials. By constructing a deeper extension of the Liu-Xia model and combining inverse participation ratio calculations with Lyapunov-exponent analysis based on Avila's global theory, we show that increasing the potential depth does not eliminate unbound states. Instead, it shifts and narrows their energy window to $-2t-V<E<2t-V$. We further extend the analysis to non-Hermitian quasiperiodic potentials with gain and loss. In these systems, unbound states survive within analytically determined real-energy intervals, but they no longer occupy the whole interval uniformly; rather, they coexist with bound states and form a mixed bound-unbound phase. The corresponding boundaries between the mixed region and the pure bound-state regions are obtained exactly from the Lyapunov exponent. These results demonstrate that unbound states in extreme quasiperiodic potentials are controlled not only by the potential depth, but also by the spectral and localization structures induced by non-Hermiticity.

Quantum many-body scars enable long-lived coherent dynamics in otherwise thermalizing systems, but controlling their stability under periodic driving remains challenging. We study the PXP model subjected to a continuous two-frequency drive and show that the frequency ratio $c={\omega }_2/{\omega }_1$ acts as a control parameter for the resulting Floquet dynamics. In a rotating-frame description, the drive generates Bessel-dressed couplings in an effective Floquet Hamiltonian whose harmonic content depends explicitly on $c$. This $c$-dependent dressing changes the competition between coherent revival dynamics and thermalization. Small integer values of $c$ stabilize scar-induced oscillations down to substantially lower driving frequencies than in the single-frequency limit. At fixed low frequency, small noninteger rational values of $c$ can instead produce isolated suppressions of coherent revivals, an effect that weakens as $c$ increases. Successive Fibonacci rational approximants also reproduce the quasiperiodic dynamics over finite observation times. We further show that two-frequency driving produces tunable rational subharmonic responses in local observables, including higher-order responses that are relatively stable for small $c$ compared with those in the corresponding single-frequency protocol. Our results demonstrate that two-frequency driving provides a route to controlling prethermal nonergodic dynamics and temporal responses in the constrained PXP model.

Boundary conditions are usually expected to cause only finite-size corrections to bulk quantities, but this expectation can fail for dynamical quantum phase transitions. In this work, we show that such boundary dependence is encoded in dynamical zero modes (DZMs) of the Loschmidt matrix, which are defined as singular vectors whose singular values vanish in the thermodynamic limit. Using the Su-Schrieffer-Heeger (SSH), extended SSH, and Kitaev models as examples, we find that the time interval where the Loschmidt rate functions (LRFs) under periodic and open boundary conditions differ coincides with the emergence of DZMs in the open-boundary Loschmidt matrix. These modes carry the boundary-dependent contribution: removing them from the open-boundary LRF recovers the periodic-boundary result. We further show that these DZMs lead to finite-precision numerical instability, since their finite-size singular values decay exponentially with system size and eventually become unresolved in fixed-precision arithmetic. A reliable small-size branch before this loss of precision can be used to estimate the LRF in the thermodynamic limit by linear extrapolation. Our results identify DZMs as both a diagnostic of boundary-dependent LRFs and the origin of the associated numerical instability.

We report near-surface small-angle neutron scattering (NS-SANS) and complementary off-specular neutron reflectometry (OSR) of the magnetic order in a single-crystalline epitaxial MnSi film grown on Si(111) in the thick-film limit. Providing a means of direct reciprocal space mapping, NS-SANS and OSR reveal one-dimensional magnetic modulations perpendicular to the film surface under magnetic fields parallel and perpendicular to the film surface, where additional polarized neutron reflectometry (PNR) and magnetization measurements are in excellent agreement with the literature. Regardless of the field orientation, our data do not suggest the presence of more complex spin textures, notably the formation of skyrmions. This observation establishes a distinct contrast to bulk MnSi thinned to similar nanoscale thicknesses, in which a skyrmion lattice dominates the phase diagram under perpendicular fields. Extended x-ray absorption fine structure measurements suggest that small shifts of the Si positions within the unstrained unit cell of the film control the magnetic state, representing the main structural difference between epitaxial and thinned bulk MnSi.

We report a systematic study of the interplay between oxygen nonstoichiometry, crystal structure, and magnetic and electrotransport properties in ${\mathrm{Sr}}_{1-x}{\mathrm{Nd}}_x{\mathrm{CoO}}_{3-\delta }$ $(x=0.1,0.2,0.3)$. High-resolution neutron powder diffraction combined with synchrotron x-ray powder diffraction reveals that increasing the oxygen content induces a structural transition from a layered $I4/mmm$ $(2a_p\times 2a_p\times 4a_p)$ phase to an oxygen-deficient orthorhombic $Pmmm$ $(a_p\times a_p\times 2a_p)$ phase with preferential oxygen-vacancy occupation. This transition is accompanied by a crossover from a G-type antiferromagnetic state with a weak ferromagnetic component to a ferromagnetic state, and a drastic decay in resistivity. The evolution of the magnetic and transport properties is discussed in terms of changes in the Co spin state, enhanced $\mathrm{Co}3d$–O $2p$ orbital overlap upon oxygen uptake, and a magnetically inhomogeneous ferromagnetic state associated with residual oxygen vacancies and mixed ${\mathrm{Co}}^{3+}$ and ${\mathrm{Co}}^{4+}$ valence. Our findings experimentally confirm that the stabilization of the layered “314” structure is driven by the presence and ordering of oxygen vacancies rather than A-site cation ordering, whereas the oxygen-deficient oxidized compounds represent an intermediate orthorhombic state preceding fully stoichiometric phases.

Identifying Majorana zero modes in semiconductor-superconductor nanowires requires ultralow temperature transport measurements in dilution refrigerators, making device screening slow and resource intensive. Here, we investigate whether high-temperature conductance data can be used to infer low-temperature Majorana nanowire properties before committing devices to dilution-refrigerator characterization. We generate paired high- and low-temperature conductance simulations for disordered Majorana nanowires and train neural networks to perform two related tasks. First, we use a shifted window U-net transformer diffusion-inspired architecture to reconstruct low-temperature conductance from thermally broadened high-temperature measurements, achieving high-fidelity recovery with $R^2\approx 0.95$ for local conductance and $R^2\approx 0.91$ for nonlocal conductance. Second, we train a video vision transformer-based network to predict the low-temperature topological visibility directly from high-temperature conductance, obtaining $R^2\approx 0.80$. These results demonstrate that machine-learning models can recover and infer low-temperature Majorana features from experimentally easier high-temperature data, providing a practical route for rejecting poor devices early thus avoiding slow and resource-intensive dilution refrigeration for nonpromising devices. This high-temperature screening approach could substantially accelerate the experimental feedback loop for Majorana nanowire device development.

Graphene has been studied in detail due to its mechanical, electrical, and thermal properties. It is well documented that the introduction of dopants or defects in the lattice can be used to tune material properties for a specific application, such as in electronics, sensors, or catalysis. To design graphene with specific properties, one must achieve control over the composition and concentration of defects. This requires a fundamental understanding of the stability of defects and their interaction in a superstructure. We present a comprehensive defect structure determination approach that enables close to exhaustive enumeration of all relevant defect structures. The approach uses a combination of density functional theory and machine learning to build a transferable energy model for defect formation. We show the capabilities of our approach for free-standing graphene with heteroatom defects, establishing a thermodynamic model to investigate how temperature affects the configuration space of doped graphene. Our analysis yields physical insights into defect interactions. A characteristic peak in the heat capacity indicates a structural transition. We provide a mechanistic explanation for this behavior and demonstrate how the transition temperature shifts with different thermodynamic reservoirs.

We theoretically demonstrate that axial phonons, lattice vibration quanta carrying finite angular momentum, can host a $d$-wave angular momentum texture in orbital altermagnets in the absence of spin-orbit coupling. We consider a minimal electronic tight-binding model with $d$-wave loop-current order that breaks time-reversal symmetry. Within the Born-Oppenheimer approximation, we incorporate electron-phonon coupling via the molecular Berry curvature and show that the underlying $d$-wave orbital magnetic moment texture of the electronic state is transferred to the phonons without requiring the relativistic spin-orbit coupling. Our results expand the range of platforms available for engineering axial phonons and point to functionality unique to $d$-wave textures, including angular-momentum Seebeck and splitter effects, corresponding to longitudinal and transverse angular-momentum currents driven by a temperature gradient.

Using time-of-flight neutron spectroscopy, we have mapped out the magnetic excitations in the van der Waals antiferromagnet ${\text{NiBr}}_2$ over a broad range of energies and momenta. The observed well-defined magnon dispersions are quantitatively reproduced by linear spin-wave theory based on a minimal bilinear Hamiltonian that includes Heisenberg exchange interactions up to third-nearest neighbors, interlayer couplings, and a single-ion anisotropy term, with no need to invoke a Kitaev interaction. This finding is consistent with the fact that bromine is lighter than iodine, leading to weaker ligand-mediated spin-orbit coupling in ${\text{NiBr}}_2$ than in ${\text{NiI}}_2$, and consequently a reduced Kitaev interaction. Our results establish ${\text{NiBr}}_2$ as a Heisenberg-dominated van der Waals antiferromagnet and support the view that the ligand spin-orbit coupling governs the strength of the bond-dependent interactions within the $\text{Ni}{\mathit{\text{X}}}_2$ (X = halogen) family.

The kagome metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ hosts an intriguing interplay between charge-density-wave (CDW) order and superconductivity that is highly sensitive to lattice distortions. However, determining the specific roles of the in-plane $\left(A_{1g,1}\right)$ and out-of-plane $\left(A_{1g,2}\right)$ symmetric strain channels has been hindered by their intrinsic mixing in conventional piezo-based experiments. Here, we combine in-plane uniaxial strain with direct $c$-axis compression to independently access and disentangle these symmetry-resolved responses in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. We reveal that $c$-axis compression drives a substantial, linear enhancement of the superconducting transition temperature $\left(T_c\right)$ alongside a suppression of $T_{\mathrm{CDW}}$. The tuning efficiency of this out-of-plane deformation acts with an opposite sign and far exceeds that of in-plane strain, demonstrating that $c$-axis lattice control dictates the phase competition. Furthermore, by isolating the pure elastoresistivity coefficients, we find that the out-of-plane cross-coupling coefficient $\left(m_{13}\right)$ is comparable in magnitude but opposite in sign to the in-plane response $(m_{11}+m_{12})$. Unlike the sharply peaked in-plane response, $m_{13}$ exhibits a distinct, order-parameter-like onset across the CDW transition. Our results establish that out-of-plane lattice control plays a dominant role in tuning the intertwined states in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ and provide a general pathway for resolving strain-coupled electronic responses in layered quantum materials.