We perform hybrid density functional calculation to study the energetics, electronic properties, optical transitions, and migration barriers of native defects in ${\mathrm{CaWO}}_4$. Oxygen and calcium vacancies are most likely to form in the absence of doping, but interstitials could also incorporate. Tungsten-related defects are unlikely to be present. The positively charged $V_{\mathrm{O}}$ and the negatively charged $V_{\mathrm{Ca}}$ are likely to form complexes. Calculated optical transition levels indicate that experimentally observed absorption and emission peaks can be attributed mainly to oxygen-related defects. Calculations of migration barriers allow us to conclude that ${\mathrm{Ca}}_i^{2+}, V_{\mathrm{O}}^{2+}$, and ${\mathrm{O}}_i^{2-}$ are highly mobile, even below room temperature. We have also examined Er dopants, finding that erbium easily substitutes on the Ca site in a positive charge state. Erbium can form complexes with $V_{\mathrm{Ca}}$ and ${\mathrm{O}}_i$, which would deactivate the Er. If Er is introduced by implantation, Er interstitials are likely present, which will produce emission that is prone to spectral diffusion and blinking. Our calculated properties of ${\mathrm{Er}}_i$ explain why annealing at modest temperatures allows the interstitials to move into substitutional sites and point defects to move away, resulting in stable emission.

We report a comprehensive high-temperature structural investigation of the B-site ordered double perovskite ${\mathrm{SrLaCoNbO}}_6$ using combined Raman spectroscopy and x-ray diffraction (XRD) over the range 25–900 ${}^{\circ }\mathrm{C}$. Two distinct temperature-driven anomalies are identified at $T_{\mathrm{OD}}=300\pm 25{}^{\circ }\mathrm{C}$ and $T_{\mathrm{PT}}=750\pm 25{}^{\circ }\mathrm{C}$ through pronounced renormalizations in the phonon frequency and linewidth, accompanied by the evolution and suppression of characteristic XRD reflections. The low-temperature anomaly at $T_{\mathrm{OD}}$ is associated with an isostructural octahedral distortion within the monoclinic $P{2}_1/n$ phase. At $T_{\mathrm{OD}}$, the radial and angular distortion parameters of the ${\mathrm{CoO}}_6$ and ${\mathrm{NbO}}_6$ octahedra decrease to near-zero values before reversing upon further heating due to an inversion of the in-plane Co–O and Nb–O bond-length hierarchy. The high-temperature anomaly at $T_{\mathrm{PT}}$ corresponds to a symmetry-breaking structural phase transition from $P{2}_1/n$ to the monoclinic $I2/m$ phase, confirmed by group-theoretical analysis and Rietveld refinement. These results demonstrate that integrating temperature-dependent Raman spectroscopy with laboratory-based XRD, complemented by quantitative octahedral distortion analysis, provides a robust approach to disentangle isostructural octahedral distortions from symmetry-breaking phase transitions in complex double perovskite oxides without recourse to synchrotron or neutron diffraction facilities.

Long-lived hyperfine coherences in rare-earth-ion doped (REID) crystals provide controlled phase evolution windows for metrology. We use this resource to propose an experimental protocol for accessing strain shifts of ground state hyperfine transitions in non-Kramers REID materials, a quantity that is difficult to access directly with conventional spectroscopic methods. Starting from the crystal field Hamiltonian, we relate the response to strain-dependent effective quadrupole and Zeeman tensors, including changes in electronic wave functions, virtual electronic admixtures, and the bare nuclear quadrupole interaction. The protocol optically prepares a selected hyperfine class, uses a phase-controlled rf $\pi /2$ pulse to create the sensing coherence, and applies synchronized dynamical decoupling pulses during the phase evolution interval so that a coherent ac strain drive accumulates phase rather than averaging away. The accumulated phase is then retrieved by Raman heterodyne readout. The resulting framework provides a route to understanding strain-induced hyperfine shifts in non-Kramers REID systems.

Solid solutions of ${\mathrm{PbZr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ (PZT) with $x\le 0.06$ undergo a phase transition from the cubic paraelectric phase to a phase usually characterized as ferroelectric. In this case, a complex system of superstructure peaks appears in the vicinity of the positions $\vec{Q}=(h+\frac{1}{2}k+\frac{1}{2}l)$, indicating the formation of incommensurate modulation of the structure. The absence of extinctions indicates a connection between the superstructure and cation displacements. A clear understanding of the relevant critical dynamics is still absent. We analyze synchrotron radiation scattering data on a PZT2.4 single crystal, focusing on diffuse scattering around the $M$ point of the Brillouin zone. We describe the data using a model that explicitly accounts for the coupling between the transverse acoustic and antiferrodistortive (AFD) phonon branches, which become symmetry allowed along the $\mathrm{\Sigma }$ line. The inverse dynamical response is represented by a $2\times 2$ matrix, and the resulting hybridized modes are used to compute the energy-integrated diffuse intensity in the high-temperature limit. The temperature dependence is governed solely by the softening of the AFD mode, which follows a Curie-Weiss law. The model successfully reproduces the observed line shapes at several temperatures. The obtained dispersion curves reveal a mixed soft mode with a minimum at an incommensurate wave vector, whose position near the phase transition agrees qualitatively with the satellite peaks observed below $T_c$. The present analysis indicates that the satellites observed in the intermediate polar phase originate from an incommensurate phase transition, driven by a mixed soft mode. Based on the obtained results, we propose a description of the observed complete pattern of superstructure reflections as a result of a transition to an incommensurate phase characterized by a 24-ray star of the wave vector $\mathbf{q}=(1/2-\delta ,1/2-\delta ,\delta )$. In this case, the $M$-type reflections turn out to be second-order reflections. The proposed description resolves the contradictions between models that interpret the observed superstructure as arising from either oxygen octahedra rotations or antiparallel cation displacements. The proposed structure is in good agreement with selected area electron diffraction data.

Two-dimensional (2D) metal borocarbide superconductors represent an emerging category of low-dimensional materials consisting of boron, carbon, and metal atoms, which hold substantial promise for applications in next-generation low-power superconducting electronics and quantum devices. Here, we design a family of 2D metal borocarbide superconductors with the chemical formula $X{\mathrm{B}}_6{\mathrm{C}}_6 (X=\mathrm{Al},\mathrm{Ga},\mathrm{In})$ using a high-throughput structural search combined with first-principles calculations. These compounds crystallize in a graphene-like metal-intercalated structure, belonging to the layer group with $P\overline{6}2m$ symmetry, where metal atoms are intercalated between the honeycomb boron–carbon (B–C) layers. These compounds have an extremely low metal content, with 83% less metal than ${\mathrm{MgB}}_2$ on a per-light-atom basis. The calculated results indicate that superconducting transition temperatures ($T_c$) of 2D ${\mathrm{InB}}_6{\mathrm{C}}_6, {\mathrm{GaB}}_6{\mathrm{C}}_6$, and ${\mathrm{AlB}}_6{\mathrm{C}}_6$ are 43.61 K, 42.20 K, and 39.97 K, respectively, all of which exceed the $T_c$ values of the conventional ${\mathrm{MgB}}_2$ superconductor (39 K). The high-$T_c$ values of these 2D metal borocarbide superconductors are mainly attributed to the strong coupling between the metallized $\sigma /\pi$ orbitals and the in-plane phonon vibrations of the B–C frameworks. These findings confirm that moderate metal doping in 2D light-element frameworks constitutes an effective strategy for achieving high-temperature superconductivity, thereby offering insights for the exploration of further superconductors.

In rare-earth ion-doped crystals, inhomogeneous absorption profiles reflect the distribution of local environments experienced by individual ions. While each optical transition probes this distribution differently, their fine spectral structures may retain correlations arising from shared local perturbations. In this paper, we present a low-temperature, high-resolution spectroscopic study in ${\mathrm{Er}}^{3+}:\mathrm{YSO}$ of the transition ${}^{4}I_{15/2}\to {}^{4}I_{11/2}$ at 980 nm and compare it to the well-known transition ${}^{4}I_{15/2}\to {}^{4}I_{13/2}$ at 1.5 $\mu \mathrm{m}$. Using spectral hole burning on one transition while monitoring the other, we uncover spectral correlations across two transitions connecting distinct spin-orbit multiplets, providing insight into the microscopic origin of inhomogeneous distributions in rare-earth doped crystals.

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 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.

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.