We present a theoretical analysis of the origin of ferromagnetism in two-dimensional Co-substituted $h$-ZnO (${h\text{−}\mathrm{Co}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}$) observed experimentally at room temperature within a narrow window of Co concentration ($x\approx 0.12$). A combination of first-principles calculations and site-occupancy disorder technique extended to include spin disorder of a large number of configurations reveals that (a) ferromagnetic (FM) and ferrimagnetic states are thermodynamically stable at $x=0.12$ at the experimental annealing temperature of $400{}^{\circ }\mathrm{C}$ and (b) FM order weakens with slight increase in $x$. The low-energy landscape is dominated by configurations with Co atoms at second-nearest-neighbor sites on the Zn sublattice exhibiting FM coupling, while higher energy configurations with Co atoms at first- and third-nearest-neighbor sites exhibit antiferromagnetic coupling. Electronic structure of the most stable FM configuration is gapped.

In iron-based superconductors (FeSCs), the interplay between electronic nematicity and superconductivity is essential for understanding the exotic superconducting ground state. In the nematic regime, in-plane strain ($\varepsilon$) tuning of the superconducting transition temperature $T_c [\mathrm{\Delta }{T}_c\left(\varepsilon \right)=\alpha \varepsilon +\beta {\varepsilon }^2]$ offers a unique approach to investigate the evolution of pairing symmetry if both $s$- and $d$-wave pairing instabilities are relevant. Here, we employ in-plane strain to tune the $T_c$ of ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$, in which both nematicity and superconductivity undergo significant changes with doping. While $T_c$ is usually suppressed quadratically with $\varepsilon$ in optimally doped ${\mathrm{BaFe}}_2{\mathrm{As}}_2, \mathrm{\Delta }{T}_c\left(\varepsilon \right)$ in ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$ dominated by $\mathrm{\Delta }{T}_c\left(\varepsilon \right)=\beta {\varepsilon }^2$ changes its sign from $\beta$ < 0 in FeSe to $\beta$ > 0 in ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$ ($x\gtrsim 0.10$), indicating an evolution of the pairing symmetry from an $s_{\pm }$ state toward an $s+d$ wave state. These findings highlight the $\mathrm{\Delta }{T}_c\left(\varepsilon \right)$ as a powerful probe for elucidating the superconducting pairing symmetry in the nematic regime of FeSCs and provide unique insights into the evolution of pairing symmetry in FeSCs.

Quantum entanglement between the spin, orbital, and lattice degrees of freedom in condensed matter systems can emerge due to an interplay between spin-orbit and vibronic interactions. Heavy transition metal ions decorated on a face-centered-cubic lattice, for example, in $5d^1$ double perovskites, are particularly suited to support these quantum entangled states, but direct evidence has not yet been presented. In this work, we report additional peaks in the low-energy spectra of a $5d^1$ double perovskite, ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$, which cannot be explained by adopting a purely classical description of lattice vibrations. Instead, our theoretical analysis demonstrates that these spectroscopic signatures are characteristic of orbital-lattice entangled states in ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$. Crucially, both theory and experiment demonstrate that these quantum-entangled states persist to low temperatures, despite the onset of multipolar order.

Graphene has emerged as a paradigmatic material in condensed matter physics due to its exceptional electronic, mechanical, and thermal properties. A deep understanding of its thermoelectric transport behavior is crucial for the development of novel nanoelectronic and energy-harvesting devices. In this work, we investigate the thermoelectric transport properties of monolayer graphene subjected to randomly distributed localized strain fields, which locally induce impurity-like perturbations. These strain-induced impurities are modeled via 2D Dirac oscillators, capturing the coupling between pseudorelativistic charge carriers and localized distortions in the lattice. Employing the semiclassical Boltzmann transport formalism, we compute the relaxation time using a scattering approach tailored to the Dirac oscillator potential. From this framework, we derive analytical expressions for the electrical conductivity, Seebeck coefficient, and thermal conductivity. The temperature dependence of the scattering centers density is also investigated. Our results reveal how strain modulates transport coefficients, highlighting the interplay between mechanical deformations and thermoelectric performance in graphene. This study provides a theoretical foundation for strain engineering in thermoelectric graphene-based devices.

Altermagnets exhibit spin-split band structures without net magnetization, offering a promising platform for unconventional spin transport and multiferroic phenomena. Based on symmetry analysis and first-principles calculations, $\mathrm{VO}{X}_2$ $(X=\text{Cl,}\text{Br,}\text{I})$ monolayers are identified as two-dimensional ferroelectric altermagnetic multiferroics, in which spin splitting is precisely tunable by switching either ferroelectric polarization or the Néel vector. Notably, the noncentrosymmetric altermagnetic structure of ${\mathrm{VOI}}_2$ gives rise to a giant, magnetically reversible bulk spin photovoltaic effect. Crystal symmetry enables a decoupling between spin and charge shift currents, allowing the generation and independent control of pure spin and pure charge photocurrents. These responses serve as internal readout mechanisms of the four ferroic multistates, enabling programmable switching via electric, magnetic, or optical fields. Our findings establish a general design strategy for nonvolatile multistate memory and nonlinear optospintronic devices based on two-dimensional multiferroics with symmetry-enabled spin-charge disentanglement.

We report a comprehensive experimental investigation of the structural, thermodynamic, static, and dynamic properties of a triangular lattice antiferromagnet ${\mathrm{Rb}}_3\mathrm{Yb}$(${\mathrm{VO}}_4{)}_2$. Through the analysis of magnetic susceptibility, magnetization, and specific heat, complemented by crystal electric field (CEF) calculations, we confirm the Kramers' doublet with effective spin $J_{\mathrm{eff}}=1/2$ ground state. Magnetic susceptibility and isothermal magnetization analysis reveal a weak antiferromagnetic interaction among the $J_{\mathrm{eff}}=1/2$ spins, characterized by a small Curie-Weiss temperature (${\theta }_{\text{CW}}^{\text{LT}}\simeq -0.26$ K) or a reduced exchange coupling ($J/k_{\mathrm{B}}\simeq 0.18$ K). The ${}^{51}\mathrm{V}$ NMR spectra and spin-lattice relaxation rate ($1/T_1$) show no evidence of magnetic long-range-order down to 1.6 K but reflect strong influence of CEF excitations in the intermediate temperatures. At low temperatures, $1/T_1\left(T\right)$ shows pronounced frequency dependence and $1/T_1$ vs field at different temperatures follows the scaling behavior, highlighting the role of paramagnetic fluctuations. The CEF calculations using the point charge approximation divulge a large energy gap ($\sim 18.61$ meV) between the lowest and second lowest energy doublets, further establishing Kramers' doublet as the ground state. Our calculations also reproduce the experimental magnetization and specific heat data and indicate an in-plane magnetic anisotropy. These findings position ${\mathrm{Rb}}_3\mathrm{Yb}$(${\mathrm{VO}}_4{)}_2$ as an ideal candidate to explore intrinsic quantum fluctuations and possible quantum spin-liquid physics in a ${\mathrm{Yb}}^{3+}$-based triangular lattice antiferromagnet.

Conventional superconductor/insulator/superconductor (SIS) Josephson junctions, devices where two superconductors are separated by a tunnel barrier, are technologically important as elements in quantum circuits, particularly with their key role in superconducting qubits. An important characteristic of Josephson junctions is the relation between the supercurrent $I_s$ and the phase difference $\phi$ between them. For SIS junctions, the current-phase relation is sinusoidal and $2\pi$ periodic. Other types of Josephson junctions, where the material between the superconductors is a weak link or a normal metal (N) may have nonsinusoidal current-phase relations that are still $2\pi$ periodic. We show here that a multiterminal diffusive SNS Josephson junction with four superconducting contacts can show a current phase relation between two of the contacts that is a superposition of $2\pi$ and $4\pi$ periodic components whose relative strength is controlled by the phase difference between the other two contacts, becoming $2\pi$ or $4\pi$ periodic for certain values of this phase difference. This tunability might have applications in tailoring the Hamiltonians of superconducting quantum circuits.

We study ${\mathbb{Z}}_2$ topological ordered phases in $2+1$ dimensions characterized by generalized modulated symmetries. Such phases have explicit realizations in terms of fixed-point Hamiltonians involving commuting projectors with support $h=3,5,7,...$ in the horizontal direction, which dictates the modulation of the generalized symmetries. These symmetries are sensitive to the lattice sizes. For certain sizes, they are spontaneously broken and the ground state is degenerated, while for the remaining ones, the symmetries are explicitly broken and the ground state is unique. The ground state dependence on the lattice sizes is a manifestation of the ultraviolet/infrared (UV/IR) mixing. The structure of the modulated symmetries implies that the anyons can move only in rigid steps of size $h$, leading to the notion of position-dependent anyons. The phases exhibit rich boundary physics with a variety of gapped phases, including trivial, partial and total symmetry-breaking, and SPT phases. Effective field theory descriptions are discussed, making transparent the relation between the generalized modulated symmetries and the restrictions on anyon mobility, incorporating the boundary physics in a natural way and showing how the short-distance details can be incorporated into the continuum by means of twisted boundary conditions.

Materials with bright excitons as the ground state are considered ideal platforms in the fields of light emission and light absorption. However, in systems with strong spin-orbit coupling, dark excitons that are exempt from spin selection rules become the ground state, leading to degraded optoelectronic performance. Two-dimensional Janus heterobilayers, with their stable intrinsic electric field from symmetry breaking, offer a promising tuning strategy for modifying excitonic states. In this work, the $\mathrm{Mo}\mathit{XY}{\mathrm{N}}_4$/$\mathrm{W}\mathit{XY}{\mathrm{N}}_4$ $(X, Y=\mathrm{Si}, \mathrm{Ge})$ heterobilayers are constructed, and their electronic and excitonic properties are calculated using the GW-BSE method. The results reveal that the synergistic interface effects and the Janus intrinsic electric field significantly modify the band alignment (type II→type I) and control the relative position of the first-bright excitonic state within the overall excitonic states, i.e., the energy difference between first-dark and first-bright excitonic states exhibits a significant increase $(0.218\to 0.836\mathrm{eV})$ or decrease $(0.218\to 0.017\mathrm{eV})$, rendering the bright exciton effectively quasidegenerate with the ground state. This work provides an important theoretical basis for the performance optimization of optoelectronic devices and deepens the understanding of exciton physics of materials.

Structural chirality gives rise to characteristic responses that change sign with the handedness of the crystal structure. One example is electrical magnetochiral anisotropy (eMChA), a change in resistivity that depends linearly on the applied current and magnetic field. Motivated by recent measurements of a strong eMChA in $p$-doped trigonal tellurium, we carry out an ab initio study of the intrinsic eMChA response in this material as a function of temperature and doping concentration. We use the semiclassical Boltzmann transport formalism within the constant relaxation time approximation to express the bulk eMChA response tensor in terms of the energy dispersion, intrinsic magnetic moment (both spin and orbital), and Berry curvature of the conduction Bloch states. We find that the orbital-Zeeman coupling dominates the calculated intrinsic response, with smaller contributions coming from the spin-Zeeman coupling and from the Berry curvature, and that the effect is maximal when both the current and magnetic field are along the trigonal axis. The calculated results show a reasonable agreement with the available experimental data. To facilitate further ab initio studies of eMChA in other materials, the code developed in this work is made available as part of the WannierBerri package.

The atomic lattice plays a critical role in the emergence of high-$T_c$ superconductivity in cuprates. While the dynamics associated with electron-lattice coupling typically unfold on picosecond-to-femtosecond timescales, we present an x-ray photon correlation spectroscopy investigation on an optimally doped La-based cuprate that reveals a strong response of kilosecond-scale lattice relaxation dynamics to the superconducting state. Notably, an anomaly emerges around $T_c$: upon cooling into the superconducting state, the average atomic relaxation lifetime decreases, i.e., dynamics accelerate. This indicates a significant change in the local disorder-induced strain field dynamics at the superconducting transition, highlighting a remarkable coupling between superconductivity and the lattice on quasistatic timescales.

The nonlinear Schrödinger equation supports solitons—self-interacting, localized states that behave as nearly independent objects. Here, we show the existence of solitons with self-induced nonreciprocal dynamics in a discrete nonlinear Schrödinger equation. This nonreciprocal behavior, dependent on soliton power and symmetry, occurs when parity is broken in a lattice with an Ablowitz-Ladik type of nonlinearity. Initially stable at high power, solitons exhibit nonreciprocal instabilities as power decreases, leading to unidirectional acceleration and amplification. This behavior is topologically protected by winding numbers on the solitons' mean-field Hamiltonian and their stability matrix, linking nonlinear dynamics and point gap topology in non-Hermitian Hamiltonians.

Ferrovalleytricity switching is the most crucial operation in valleytronics. In current valleytronic research, it is predominately realized by magnetic field, which is not favored in terms of efficiency. Here, we propose a mechanism that allows ferrovalleytricity switching fully controlled by voltage pulses. The physics correlates to the peculiar magnetoelectric coupling in multiferroic heterobilayers, where the reversal of ferroelectric polarization reverses interlayer magnetic ground order. We show that such coupling can enable the reversal of spin orientation and consequently the ferrovalleytronic polarization of carriers through purely electric means, thereby achieving electrically switchable ferrovalleytricity. Using first-principles calculations, we further validate this mechanism in the multiferroic heterobilayer ${\mathrm{CuCrP}}_2{\mathrm{S}}_6/{\mathrm{CrBr}}_3$. The significant disparity in magnetic anisotropy of two constitute layers is identified to play a vital role in realizing the mechanism. Our findings establish a promising route toward the electric field control of ferrovalleytricity.

Based on the strong-disorder renormalization group method, a microscopic mechanism of defect formation in the quantum annealing of the random transverse-field Ising chain is proposed, which represents the annealing process as a gradual aggregation of strongly coupled spin clusters. The ferromagnetic ground state of clusters is either preserved or gets excited in pairwise fusions of clusters, depending on the effective annealing rate of the fusion, the latter events being responsible for the appearance of defects in the final state. A consequence of the theory is that, although the Griffiths-McCoy phases surrounding the critical point are gapless, they are still effectively gapped from the point of view of quantum annealing. Thereby, we provide an explanation of the finiteness of the gap outside the critical point, which was implicit in an early approach to the problem by Kibble-Zurek scaling [Dziarmaga, Phys. Rev. B 74, 064416 (2006)]. Furthermore, by identifying the accessible excitations, we refine the functional form of the vanishing of the gap at the critical point. The defect density in the final state is found to decrease with the annealing time $\tau$, as $n\left(\tau \right)\sim {ln}^{-2}\left(\frac{\tau }{{ln}^2\tau }\right)$ for large $\tau$. In addition to this, our approach gives access also to the density of defects at intermediate times of the annealing process.

Crystalline symmetry can be used to predict bulk and surface properties of topological phases. For noninteracting cases, symmetry-eigenvalue analysis of Bloch states at high-symmetry points in the Brillouin zone simplifies the calculation of topological quantities. However, when open boundaries are present, and only the point-group part of the symmetry group remains, it is unclear how to utilize crystalline symmetries to diagnose band topology. In this work, we introduce topological crystalline markers to characterize bulk topology in $C_n$-symmetric ($n=2,3,4,6$) crystalline insulators and superconductors with and without translation symmetry. These markers are expressed using a crystalline-symmetry operator and the ground-state projector, and are defined locally in position space. First, we provide a general method to calculate topological markers in periodic systems with an arbitrary number of unit cells. This includes cases where momentum quantization does not span all necessary high-symmetry points for computing the topological quantities, which we address using twisted boundary conditions. Second, we map these markers to the Chern number, bulk polarization, and sector charge for two-dimensional $C_n$-symmetric insulators in symmetry classes A, AI, AII, and superconductors in class D. Finally, we show how to numerically calculate the markers in finite-size systems with translation-symmetry (and even rotation-symmetry) breaking defects, and how to diagnose the bulk topology from the marker. Our results demonstrate how to compute bulk topological crystalline invariants locally in position space, thereby providing broader scope to diagnosing bulk crystalline topology that works even in inhomogeneous systems where there is no global rotation symmetry.

We investigate high-harmonic generation (HHG) in a dimerized Kitaev chain. The dimerization in the model is introduced through a site-dependent modulating potential, determined by a parameter $\lambda \in [-1:1]$. This parameter also determines the strength of the hopping amplitudes and tunes the system's topology. Depending upon the parameter $\lambda$, the HHG emission spectrum can be classified into three segments. The first segment exhibits two plateau structures, with the dominant one resulting from transitions to the chiral partner state, consistent with quasiparticle behavior in the topological superconducting phase. The second segment displays multiple plateaus, where intermediate states enable various transition pathways to higher conduction bands. Finally, the third segment presents broader plateaus, indicative of active interband transitions. In the $\lambda \le 0$ regime, we observe the midgap states (MGSs) hybridize with the bulk, suppressing the earlier observed harmonic enhancements. This highlights the key role of the intermediate states, particularly when MGSs are isolated. These results demonstrate that harmonic emission profiles can be selectively controlled through the modulating parameter $\lambda$, offering new prospects for tailoring HHG in topological systems.