Altermagnets (AMs) are an exotic class of antiferromagnet that exhibit spin splitting even in the absence of net global magnetization and spin-orbit coupling (SOC) effects. In this work, we investigated theoretically the supercurrent nonreciprocity in an Ising-superconductor (ISC)/altermagnet/Ising-superconductor Josephson junction which revealed asymmetric Josephson critical currents, $0\text{−}\pi$ transitions, and an anomalous current-phase relation. A strong Josephson diode efficiency (JDE) is observed due to the combined effects of AM strength and orientations in a conventional superconductor even in absence of SOC. However, it significantly enhances in presence of intrinsic SOC (ISOC), resulting in pronounced diode effect in both the single- and double-band ISC/AM based Josephson junction. Additionally, it is observed that JDE is more prominent at higher AM strengths with intermediate orientations in all scenarios. Notably, it is significantly suppressed for orientations $0^{\circ }$ and ${45}^{\circ }$. Our results also indicate that barrier transparency and AM lengths play a crucial role in optimizing the JDE. In a single-band ISC/AM system JDE persists for any AM length, while it reduces at longer AM junctions in case of a double-band ISC/AM system. Moreover, our results suggest that a diode efficiency of $\approx 52\%$ can be achieved in the proposed Josephson junction in both the single- and double-band ISC/AM Josephson junction by considering strong AM strength. Furthermore, the single-band ISC offers a wide AM orientation range in contrast to the double-band ISC for better tunability and optimization of JDE. Our findings highlight the impact of AM strength, orientation, and ISOC on the JDE efficiency, offering insights for superconducting diode design.

Recent angle-resolved photoemission spectroscopy (ARPES) experiments on ${\mathrm{La}}_{2.85}{\mathrm{Pr}}_{0.15}{\mathrm{Ni}}_2{\mathrm{O}}_7$ thin films revealed a superconducting gap near the diagonal direction for the $d_{x^2-y^2}$ orbital, confined to a narrow momentum region. Our numerical calculations indicate that interlayer pairing is dominant, resulting in an $s_{\pm }$-wave symmetry. We propose employing perpendicular electric fields, a practical method in thin-film systems, to verify the pairing symmetry. Our calculations predict that such fields will induce Fermi arcs or nodal points and significantly modulate the gap near the diagonal, with the modulated region overlapping the area probed by ARPES. This approach provides an effective tool for probing pairing symmetry in bilayer nickelate thin films, especially given current limitations in experimental techniques.

Bose-Einstein condensate of dark intervalley excitons must be inherently multicomponent because of crystalline symmetries. Since valleys hosting such excitons are separated by large quasimomenta, a minimal intercomponent Josephson-type coupling can only be established between pairs of excitons from the time-reversed valleys. As a result, a paired condensate can emerge at finite temperature, that is, the off-diagonal order exists for the pairs from the time-reversed valleys, while the individual valleys are disordered. This prediction follows from the elementary mean-field analysis regardless of the dimensionality. However, as Monte Carlo simulations show, no such a phase exists in three-dimensional (3D) crystals. Instead, the multicomponent condensation proceeds as the first-order transition from the normal state. The paired phase does exist in two dimensions (2D) for the number of the components, $N_v\ge 6$. It forms by Berezinskii-Kosterlitz-Thouless transition from the high-temperature (normal) phase. The multicomponent condensate appears upon further lowering of the temperature.

Emerging experimental platforms use amorphousness, a constrained form of disorder, to tailor metamaterial properties. We study localization under this type of disorder in a family of two-dimensional models generalizing recent experiments on photonic systems. Models in this family reside on amorphous analogs of kagome lattices with fixed coordination number, vary by a tunable synthetic field, and remarkably, permit exact results. We observe two kinds of localization that emerge in these models: Anderson localization by amorphous disorder, and the existence of compact, macroscopically degenerate localized states as in many crystalline flat bands. The flat-band-like degeneracy innate to kagome lattices survives under amorphousness without onsite disorder. This phenomenon arises from the cooperation between the structure of the compact localized states and the geometry of the amorphous graph. More surprisingly, for particular values of the field, such states emerge in the amorphous system that were not present on the kagome lattice in the same field. Outside the flat band, constrained amorphous graph geometry necessitates the existence of a fully delocalized state, near which we observe evidence of a localization-delocalization transition. Our platform serves as a demonstration of how the qualitative behavior of a disordered system can be tuned at fixed graph topology and lead to localization phenomena unique to amorphous systems that are not observed in their generically disordered counterparts.

Many-body-localization (MBL) transitions are studied in a family of single-spin-flip spin-$\frac{1}{2}$ models, including the one-dimensional (1D) chain with nearest-neighbor interactions, the quantum dot (QD) model with all-to-all pair interactions, and the quantum random energy model (QREM). We investigate the generalized imbalance that characterizes propagation in Fock space out of an initial basis state and, at the same time, can be efficiently probed by real-space measurements. For all models considered, the average imbalance and its quantum and mesoscopic fluctuations provide excellent indicators for the position of the MBL transition $W_c\left(n\right)$, where $n$ is the number of spins. Combining these findings with earlier results on level statistics, we determine phase diagrams of the MBL transitions in the $n\text{−}W$ plane. Our results provide evidence for a direct transition between the ergodic and MBL phases for each of the models, without any intermediate phase. For QREM and QD model, $W_c\left(n\right)$ grows as a power law of $n$ (with logarithmic corrections), in agreement with analytical predictions $W_c^{\mathrm{QREM}}\left(n\right)\sim n^{1/2}lnn$ and $W_c^{\mathrm{QD}}\left(n\right)\gtrsim n^{3/4}{ln}^{1/2}n$. This growth is in stark contrast to the 1D model, where $W_c\left(n\right)$ is essentially independent of $n$, consistent with the analytic expectation $W_c^{1\mathrm{D}}(n\to \infty )=\mathrm{const}$. We also determine the scaling of the transition width $\mathrm{\Delta }W\left(n\right)/W_c\left(n\right)$ and estimate the system size $n$ needed to study the asymptotic scaling behavior. Although the corresponding values of $n$ are larger than those accessible to exact simulations on a classical computer, they are within the reach of quantum simulators. Our results indicate feasibility of experimental studies of $n\text{−}W$ phase diagrams and scaling properties of MBL transitions in models of 1D and QD type and in their extensions to other spatial geometry or distance-dependent interactions.

Spatial topology not only classifies static magnetic textures by magnetization, but also categorizes dynamic spin waves by flow. Here we establish the topological connections between the order and flow in the same magnetic system, and further propose to use the vortices developing in spin waves to probe the essential information of the background magnetic texture. Particularly, the cores of these spin-wave vortices indicate texture magnetization along a specific direction, the windings reveal the texture topology, and their chart yields a unified relation for the topological magnon Hall angle. The geometric relations established purely upon the transverse precession of spin waves about the texture magnetization provide an integrated description of the static and dynamic magnetic phenomena. By utilizing topological defects in excitations to acquire the key features of the background medium, the vortex acts as a powerful toolkit to explore and exploit the functionalities embedded in complex structures.

Perfect circular dichroism has been observed in Raman scattering by optical phonons in single chiral domain $\mathrm{Ni}{\mathrm{Co}}_2\mathrm{Te}{\mathrm{O}}_6$ crystals. The selection rules for optical phonons are determined by the combination of the chiral structure $C$ and electric polarization P along the $c$ axis. These two symmetry operations are equivalent to the ferroaxial order ($C$·P) = A, so the observed optical phonons are referred to as ferroaxial. For a given Raman scattering geometry, the observed effect may also be described as a perfect nonreciprocal propagation of the ferroaxial optical phonons, whose preferable $\vec{q}$-vector direction is determined by the sign of A. The combination of Raman scattering and polarization plane rotation of the transmitted white light allows for identification of the direction of electric polarization P in monodomain chiral crystals. In addition to the ferroaxial selection rules for optical phonons, a weaker ferroaxial dichroism was observed for the magnon peak at 18 $\mathrm{c}{\mathrm{m}}^{-1}$.

We study the antiferromagnetic XXZ chain with longitudinal boundary magnetic fields using numerical diagonalization and the exact Bethe ansatz solution. We identify a phase transition at $h_w=-\mathrm{\Delta }+1$ (with $\mathrm{\Delta }>1$) as a continuous wetting transition, in which the domain wall delocalizes from the boundary at the transition point. From the exact solution, we obtain both the energy gap and the boundary magnetization. We then propose a perturbation approximation, whose predictions for the energy gap and boundary magnetization closely match the exact results. The universal magnetization profile at the critical point is obtained. Using this approximation, we also compute the correlation function and, in turn, determine the correlation length and the thickness of the wetting layer. The correlation length, the wetting layer thickness, and the dynamical critical exponents are $\nu =1, {\beta }_s=1$, and $z=2$, respectively, together with the universal magnetization profile at the critical point, indicating that the transition belongs to the Ising universality class.

The creation and control of magnetic spin textures is of great interest in fundamental research and future device-oriented applications. Fe/Gd multilayers host a rich variety of magnetic textures including topologically trivial type-2 bubbles and topologically protected chiral type-1 bubbles, also known as dipolar-stabilized skyrmions. Using time-resolved Kerr spectroscopy, we highlight how various control strategies, including temperature, out-of-plane magnetic fields and femtosecond light excitation, can be used to create such textures via different pathways. We find that varying the magnetic field for constant temperature leads to a different ($H,T$) phase diagram of magnetic textures than moving along a temperature trajectory for constant magnetic field. Micromagnetic simulations corroborate this finding and allow us to visualize the different paths taken. Furthermore, we show that the creation of bubbles and skyrmions in this material via impulsive light excitation is not solely governed by temperature-driven processes, since bubbles and skyrmions can be stabilized in parts of the ($H,T$) phase diagram, where neither the constant temperature nor the constant magnetic field trajectory predict their existence. Using this phase diagram, we reason why bubble and skyrmion creation in this particular system is only possible from the stripe domain state. Our observations provide a versatile toolkit for tailoring the creation of magnetic spin textures in Fe/Gd multilayers.

We have investigated the changes in the magnetic properties on ${\mathrm{YbCuS}}_2$ by Lu or Se substitutions from a microscopic perspective. In general, it is expected that nonmagnetic Lu substitution dilutes the magnetic ${\mathrm{Yb}}^{3+}$ concentration and that Se substitution induces the negative pressure in ${\mathrm{YbCuS}}_2$. The ${}^{63/65}\mathrm{Cu}$-nuclear quadrupole resonance (NQR) measurements on polycrystalline ${\mathrm{Yb}}_{0.9}{\mathrm{Lu}}_{0.1}{\mathrm{CuS}}_2$ and $\mathrm{YbCu}{\left({\mathrm{S}}_{0.9}{\mathrm{Se}}_{0.1}\right)}_2$ revealed that the Se substitution leads to larger lattice expansion compared to the Lu substitution. The antiferromagnetic transition temperature $T_{\mathrm{N}}$ decreased from 0.95 K in the unsubstituted system to 0.75 K in both substituted systems. Furthermore, the $T$-linear behavior of the ${}^{63}\mathrm{Cu}$-NQR spin-lattice relaxation rate $1/T_1$, suggesting the presence of the gapless quasiparticle excitations, was observed even in the substituted systems and the value of $1/T_{1}T$ increases. These results under the chemical substitutions are opposite to those under pressure as previously reported and are consistent with the expectation. Our systematic study indicates a clear relationship between the magnetic ordered states and the quasiparticle excitations in ${\mathrm{YbCuS}}_2$.

Obstructed atomic phases, with their realizations in systems of diverse dimensionality, have recently arisen as one of the topological states with greatest potential to show higher-order phenomena. In this work we report a special type of obstruction, known as orbital-mediated atomic obstruction, in monolayers of materials with crystalline symmetry described by the space group $P\overline{3}m1$. By means of a minimal tight-binding model and first-principles calculations, we show that this obstructed phase is related to the mismatch of the charge centers coming from the atomic limit with respect to the centers that are obtained from a reciprocal space description. Although we find atomic limits that correspond with occupied atomic sites, orbital-mediated atomic obstruction requires the presence of orbitals that have no support in real space. In order to demonstrate the nontrivial character of the obstruction, we confirm the presence of a filling anomaly for finite geometries that is directly associated with the bulk configuration, and discuss the role of the boundary states and their underlying mechanism. Several material examples are presented to illustrate the ubiquity of these nontrivial responses and, in turn, to discuss the differences related to the particular ground-state configuration. In addition, we perform a survey of materials and elaborate a list of candidate systems which will host this obstructed phase in monolayer form.

Bulk ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ (MBT) is an intrinsic antiferromagnetic topological insulator. However, its low Néel temperature of $\sim 25$ K severely restricts its practical applications. Here, we propose a van der Waals heterostructure composed of monolayer MBT (ML-MBT) and monolayer ${\mathrm{MnBr}}_3$, an intrinsic Chern insulator possessing a high Curie temperature ($T_C\sim 200\mathrm{K}$). By employing density functional theory calculations and Monte Carlo simulations, we demonstrate that interfacing ML-MBT with ${\mathrm{MnBr}}_3$ significantly enhances the $T_C$ of ML-MBT by a factor of four to five. Electronic correlations characterized by the Hubbard parameter $U_2$ for Mn-$d$ orbitals in ${\mathrm{MnBr}}_3$ play a crucial role in governing magnetic coupling within the system. At a moderate correlation strength of $U_2=3.0\mathrm{eV}$, slight structural distortions in ${\mathrm{MnBr}}_3$ break intralayer symmetry, enabling robust interlayer ferromagnetic coupling and yielding a single, unified magnetic transition. Increasing $U_2$ reduces these structural distortions, weakens interlayer coupling, and induces two distinct magnetic transitions, indicating interlayer magnetic decoupling. Thus, the $\mathrm{MBT}/{\mathrm{MnBr}}_3$ heterostructure offers an interesting approach for controlling magnetic order and enhancing the performance of spintronic devices.

Asymmetric transmissions have a number of significant applications in a variety of fields, including communication and sensing systems. In this study, we present the numerical simulations of a single phonon diode model comprising a metagrating and a superlattice structure. By breaking the spatial inversion symmetry, the unidirectional transmission of a single phonon can be achieved in the proposed setup. This unidirectional phenomenon can be attributed to the occurrence of distinct mode transitions at two sides of the diode. Moreover, we demonstrate that the precise control of energy flow partition passing through the metagrating can be achieved by optimizing the metagrating parameters via machine learning, resulting in a significant contrast between the energy transmission in two directions, up to two orders of magnitude. The physical mechanisms to achieve enhanced rectification efficiency are discussed in detail. This work therefore paves a feasible pathway in designing functional phononic devices based on stylized metagrating structures.

Implementing an improved method for analytic continuation and working with imaginary-time correlation functions computed using quantum Monte Carlo simulations, we resolve the single-particle dispersion relation and the density of states (DOS) of the two-dimensional Hubbard model at half filling. At intermediate interactions of $U/t=4,6$, we find quadratic dispersion around the gap minimum at wave vectors $\mathbf{k}=(\pm \pi /2,\pm \pi /2)$ (the $\mathrm{\Sigma }$ points). We find saddle points at $\mathbf{k}=(\pm \pi ,0),(0,\pm \pi )$ (the $X$ points), where the dispersion is approximately quartic, leading to a sharp DOS maximum above the almost flat ledge arising from the states close to $\mathrm{\Sigma }$. The fraction of quasiparticle states within the ledge is $n_{\mathrm{ledge}}\approx 0.15$. Upon doping away from half filling, within the rigid-band approximation, these results support Fermi pockets around the $\mathrm{\Sigma }$ points, with states around the $X$ points becoming filled only at doping fractions $x\ge n_{\mathrm{ledge}}$. The high density of states away from the $\mathrm{\Sigma }$ gap edge may be an important clue for a finite minimum doping level for superconductivity and other instabilities of doped Mott insulators.

We develop a density matrix renormalization group (DMRG) algorithm for constrained quantum lattice models that successfully implements the local constraints as symmetries in the contraction of the matrix product states and matrix product operators. Such an implementation allows us to investigate a quantum dimer model in DMRG for any lattice geometry wrapped around a cylinder with substantial circumference. We have thence computed the ground-state phase diagram of the quantum dimer model on a triangular lattice, with the symmetry-breaking characteristics of the columnar solid phase and $\sqrt{12}\times \sqrt{12}$ valence bond solid phase fully captured, as well as the topological entanglement entropy of the ${\mathbb{Z}}_2$ quantum spin-liquid phase that extends to the Rokhsar-Kivelson point on nonbipartite lattice accurately revealed. Our DMRG algorithm opens new opportunities for tensor-based approaches to constrained models, including but not limited to dimer-type systems. Such models are often directly relevant to frustrated quantum magnets and synthetic quantum simulators.

The layer-dependent electronic and thermal transport properties of phosphorene offer a unique platform for designing high-performance thermoelectric devices. Here, we employ a combination of density functional theory and nonequilibrium Green's function formalism to investigate the thermoelectric performance of phosphorene-based transistors with spatially modulated layer thicknesses. By engineering the thickness of the active region from four layers to a single monolayer, we demonstrate a significant enhancement in the thermoelectric figure of merit $\left(ZT\right)$, achieving $ZT\approx 1.1$ at 300 $\mathrm{K}$ for transport along the armchair direction: a threefold increase over uniform four-layer devices. This improvement arises from the interplay between suppressed phonon thermal conductivity (reduced by $70\%$ via interfacial scattering) and maintained high electrical conductivity due to tailored band alignment and anisotropic charge transport. The armchair-oriented devices outperform zigzag configurations owing to their lower lattice thermal conductivity, despite the latter's superior power factor. Phonon transport calculations, utilizing Stillinger-Weber potentials and Green's function methods, reveal that thickness gradients induce strong backscattering, effectively decoupling electronic and thermal transport. Furthermore, the transition to monolayer regions creates a type-I heterojunction, enhancing thermopower while minimizing parasitic heat dissipation. Our results not only establish phosphorene as a versatile candidate for on-chip energy harvesting, but also provide a general framework for leveraging dimensionality and anisotropy in van der Waals heterostructures to optimize thermoelectric efficiency.

The quantum properties of nitrogen-vacancy $\left({\mathrm{NV}}^{-}\right)$ centers in diamond have laid the foundation for solid-state quantum bit (qubit) applications. However, as the demand for quantum computing and communication grows, the exploration of new materials has become essential. In recent years, two-dimensional (2D) materials have shown tremendous potential in qubit research due to their rich quantum phenomena, high tunability, and ease of integration. In this study, based on first-principles calculations, we propose that 2D $1T$-phase ${\mathrm{SnO}}_2$ monolayer is an experimentally viable qubit host material. With an ultrawide band gap of 4.11 eV, $1T\text{−}{\mathrm{SnO}}_2$ monolayer exhibits phosphorus-oxygen $\left({\mathrm{P}}_{\text{O}}\right)$ defects that possess stable spin doublet $(S=1/2)$ and spin triplet $(S=1)$ ground states, which are preserved during optical excitation—a critical requirement for qubit functionality. Our calculations show that ${\mathrm{P}}_{\text{O}}^0$ and ${\mathrm{P}}_{\text{O}}^{+1}$ defects are stable within a Fermi level range of 0 to 2.88 eV. Their zero-phonon lines (ZPL) of 0.65 and 0.52 eV, respectively, fall within the infrared region, making them suitable for optical detection and microwave control. The dimensional reduction in 2D $1T\text{−}{\mathrm{SnO}}_2$ monolayer is predicted to weaken the hyperfine interaction, improving qubit performance. The ${\mathrm{P}}_{\text{O}}$ defect centers in ${\mathrm{SnO}}_2$ provide a promising solution for solid-state qubit applications. Future experimental studies are expected to validate these theoretical predictions, offering important support for the advancement of quantum computing and communication technologies.