We report on the discovery of field-induced large colossal magnetoresistance (CMR) of ∼ −${10}^{14}\%$ and angular magnetoresistance (AMR) ∼ ${10}^{14}\%$ achieved simultaneously in an antiferromagnetic rare-earth dichalcogenide ${\mathrm{EuSe}}_2$. Such intriguing observations are attributed to strong magnetic anisotropy and magnetic-field induced antiferromagnetic to ferromagnetic transition of the localized $\mathrm{E}{\mathrm{u}}^{2+}$ spins, which in turn closes the bandgap by lifting the degeneracy of Se-$5p$ bands near Fermi level. Our density functional theory calculations perfectly replicate the experimental findings based on the Brillouin function and carries transport model. The present work provides a potential simple antiferromagnetic material for achieving angle-sensitive spintronic devices.

We investigate one-dimensional (1D) and 2D cluster states under local decoherence to assess the robustness of their mixed-state subsystem symmetry-protected topological (SSPT) order. By exactly computing fidelity correlators via dimensional reduction of effective statistical mechanics models, we pinpoint the critical error rate for strong-to-weak spontaneous breaking of strong subsystem symmetry. Without resorting to the replica trick, we demonstrate that mixed-state SSPT order remains remarkably robust up to the maximal decoherence rate when noise respects strong subsystem symmetry. Furthermore, we propose that the mixed-state SSPT order can be detected by a constant correction to the area-law scaling of entanglement negativity, termed spurious topological entanglement negativity. This also highlights that topological entanglement negativity, a widely used diagnostic for mixed-state topological order, is generally not invariant under finite-depth quantum channels.

While a generic open quantum system decays to its steady state, continuous time crystals (CTCs) develop spontaneous oscillation and never converge to a stationary state. Just as crystals develop correlations in space, CTCs do so in time. Here, we introduce a continuous quasi time crystals (CQTC). Despite being characterized by the presence of nondecaying oscillations, this phase does not retain its long-range order, making it time analogous to quasicrystal structures. We investigate the emergence of this phase in a minimal model, made of two coupled collective spin subsystems, each developing a CTC phase upon the action of a strong enough drive. The addition of a coupling enables the emergence of different synchronized phases, where both subsystems oscillate at the same frequency. In the transition between different CTC orders, the system develops chaotic dynamics with aperiodic oscillations. These chaotic features differ from those of closed quantum systems, as the dynamics is not characterized by a unitary evolution. We investigate the connection between chaos and this quasicrystalline phase using mean-field techniques, and we confirm these results by including quantum fluctuations at the lowest order.

Second-harmonic generation [SHG, $I\left(2\omega \right)$] of the three-dimensional topological insulators (3D TIs) provides significant insights into the nontrivial band topology through the second-order nonlinear susceptibility ${\chi }^{\left(2\right)}$ of the topological surface states (TSSs), along with the electric-field-induced SHG resulting from band bending (given by ${\chi }^{\left(3\right)}{E}_{\text{dc}}$). Notably, by carefully tuning the polarization of the incident laser field, second-harmonic intensity measurements make it possible to isolate and analyze the distinct contributions from the bulk $\left({\chi }^{\left(3\right)}{E}_{\text{dc}}\right)$ and the metallic surface states $\left({\chi }^{\left(2\right)}\right)$. Recently reported Sb-doped quaternary alloy ${\mathrm{Bi}}_{2-x}{\mathrm{Sb}}_x{\mathrm{Te}}_{3-y}{\mathrm{Se}}_y$, isostructural to conventional TIs, provides a suitable platform for studying the TSS due to its high bulk resistivity and the Dirac point lying within the bulk band gap. In this work, we report the enhancement of $I\left(2\omega \right)$ upon the application of circularly polarized light, attributed to the breaking of the time-reversal symmetry in the TSS of ${\mathrm{BiSbTe}}_{1.25}{\mathrm{Se}}_{1.75}$ crystal. Additionally, the differential change in SHG intensity $\left[\mathrm{\Delta }I\left({\tau }_{\text{pp}}\right)\right]$ as a function of pump-probe delay time $\left({\tau }_{\text{pp}}\right)$ for a linearly polarized probe exhibits two competing contributions to $E_{\text{dc}}$ from the surface and the bulk. The surface contribution is more pronounced than the bulk contribution, owing to the system's bulk insulating nature. Interestingly, by changing the probe polarization from linear to circular, we show that the second-harmonic response has an additional contribution from ${\chi }^{\left(2\right)}$, thereby extracting the time evolution of $\mathrm{\Delta }{\chi }^{\left(2\right)}\left({\tau }_{\text{pp}}\right)$ arising from the TSS after photoexcitation. Furthermore, we justify the time-dependent second-order response of the TSS by analytically solving the second-order conductivity $\left({\sigma }^{\left(2\right)}\right)$, including the band gap opening at the Dirac point, which depicts a sign change in $\mathrm{\Delta }I$ depending on the shape of the Fermi surface.

The delafossitelike compound ${\mathrm{NaYbO}}_2$ hosts a triangular lattice of ${\mathrm{Yb}}^{3+}$ moments and is a promising candidate for the realization of a quantum spin liquid ground state—an exotic, quantum-disordered magnetic phase featuring long-range entanglement of spins. Tuning this system away from this quantum-disordered regime toward classical order or spin freezing is a powerful approach to shed light on the nature of the parent ground state. Here we leverage the substitution of nonmagnetic ${\mathrm{Lu}}^{3+}$ onto the ${\mathrm{Yb}}^{3+}$ sites to study the effects of magnetic disorder in ${\mathrm{NaYbO}}_2$ using low-temperature ac susceptibility, heat capacity, and muon spin relaxation ($\mu \mathrm{SR}$) measurements. Our $\mu \mathrm{SR}$ measurements reveal resilient, correlated magnetic fluctuations that persist to at least 15% dilution, precluding conventional spin freezing and magnetic inhomogeneity. Heat capacity and magnetic susceptibility resolve a rapid suppression of the field-induced “up-up-down” magnetic order upon dilution and a crossover in the power-law behavior of the low-temperature magnetic excitations associated with the zero-field quantum disordered ground state. Taken together, these results support the notion of a robust network of entangled moments in ${\mathrm{NaYbO}}_2$ and provide experimental validation of several models of a Heisenberg triangular lattice antiferromagnet in the presence of disorder.

Lanthanide ($Ln$) based $Ln\mathrm{SbTe}$ materials have garnered significant attention due to the rich interplay of long-range magnetic ordering and topological properties, driven by unique crystalline symmetry, $4f$ electron interactions, and pronounced spin-orbit coupling (SOC) effects. DySbTe, as a heavier lanthanide based member of the $Ln\mathrm{SbTe}$ family, stands out with its SOC and larger on-site interactions on its $4f$ electrons, which arise due to the heavier Dy element. Here, we present a comprehensive study on the low-temperature bulk physical properties and the electronic structure of DySbTe using magnetic susceptibility, heat capacity, and electrical resistivity measurements, along with high-resolution angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy and spectroscopy (STM/S), and density functional theory calculations. Our thermodynamic measurements revealed an antiferromagnetic ordering below $T_{\mathrm{N}}=7.45$ K and a subsequent magnetic phase transition at $T_{\mathrm{N}1}=7.15$ K. Our transport studies indicate a semimetallic behavior with unusual feature in the ordered state. Our ARPES measurements revealed a diamond-shaped Fermi pocket centered at the $\overline{\mathrm{\Gamma }}$ point, with band features that evolve distinctly across various binding energies. STM/S results indicate a minimum in the density of states at around 100 meV below the Fermi level, and ARPES measurements reveal a significant gap present around the $\overline{\mathrm{X}}$ point, differentiating DySbTe from other $Ln\mathrm{SbTe}$ compounds. These findings enhance our understanding of the SOC effects on the electronic structure and topological properties in the $Ln\mathrm{SbTe}$ family, highlighting DySbTe as a promising candidate for exploring the interplay between topology and magnetism.

We study the effects of strain on exciton dynamics in transition metal dichalcogenide (TMD) nanoribbons. Using the Bethe–Salpeter formalism, we derive the exciton dispersion relation in strained TMDs and demonstrate that strain-induced pseudogauge fields significantly influence exciton transport and interactions. Our results show that low-energy excitons occur at finite center-of-mass momentum, leading to modified diffusion properties. Furthermore, the exciton dipole moment depends on center-of-mass momentum, which enhances exciton-exciton interactions. These findings highlight the potential of strain engineering as a powerful tool for controlling exciton transport and interactions in nanoribbon-based TMD optoelectronic and quantum devices.

Nonlocal quantum games provide proof of principle that quantum resources can confer an advantage at certain tasks. They also provide a compelling way to explore the computational utility of phases of matter on quantum hardware. In a recent paper [O. Hart et al., Phys. Rev. Lett. 134, 130602 (2025)], we demonstrated that a toric code resource state conferred advantage at a certain nonlocal game, which remained robust to small deformations of the resource state. In this paper we demonstrate that this robust advantage is a generic property of resource states drawn from topological or fracton ordered phases of quantum matter. To this end, we illustrate how several other states from paradigmatic topological and fracton ordered phases can function as resources for suitably defined nonlocal games, notably the three-dimensional toric-code phase, the X-cube fracton phase, and the double-semion phase. The key in every case is to design a nonlocal game that harnesses the characteristic braiding processes of a quantum phase as a source of contextuality. We unify the strategies that take advantage of mutual statistics by relating the operators to be measured to order and disorder parameters of an underlying generalized symmetry-breaking phase transition. Additionally, by connecting the win probability to twist products, we show that success at the game serves as a many-body entanglement witness. Namely, if the players implement a perfect quantum strategy on large length scales, the quantum state they share cannot be connected to a trivial product state via a constant-depth local unitary circuit. Finally, we massively generalize the family of games that admit perfect strategies when codewords of homological quantum error-correcting codes are used as resources.

We find that the behaviors of the voltage-current characteristics as one enters the low-density insulating state and integer quantum Hall insulating states in the ultraclean two-dimensional electron system in SiGe/Si/SiGe quantum wells are qualitatively different. The double-threshold voltage-current curves, representative of the electron solid formation at low densities, are not observed in the quantum Hall regime, which does not confirm the existence of a quasiparticle quantum Hall Wigner solid and indicates that quasiparticles near integer filling do not form an independent subsystem.

We propose a general framework for constructing self-dual one-dimensional quasiperiodic lattice models with arbitrary-range hoppings and multifractal behaviors. Our framework generates a broad spectrum of one-dimensional quasicrystals, ranging from the off-diagonal Aubry-André-Harper models on one end, to those featuring long-range hoppings with varied quasiperiodic modulations on another. Focusing on models with off-diagonal quasiperiodic hoppings with power-law decay, we exploit the fact that, when the self-dual condition is satisfied, the system must be in the critical state with multifractal properties. This enables the engineering of models with competing extended, critical, and localized phases, with richly structured mobility edges separating them. As an outstanding example, we show that a limiting case of our family of self-dual quasicrystals can be implemented using Rydberg-atom arrays. Our work offers a systematic route toward critical phases from self-duality considerations, and would facilitate the experimental simulation of these exotic states.

Motivated by a recent debate about the origin of remanent magnetization and the corresponding anomalous Hall effect in antiferromagnets and altermagnets, a theory of bound magnetic polarons (BMPs) in anisotropic magnetic semiconductors is developed. The theory describes quantitatively the experimentally observed magnitude of excess magnetization and its dependence on the magnetic field in cubic antiferromagnetic EuTe. In contrast to the cubic case, our theory predicts the presence of magnetization hysteresis below Néel temperature in antiferromagnets with uniaxial anisotropy. We show, employing material parameters implied by experimental and ab initio results, that the magnitudes of remanent magnetization and the coercive field are in accord with recent experimental observations for altermagnetic hexagonal MnTe. While the altermagnets have an intrinsic contribution to the remanent magnetization and the anomalous Hall effect, our theory explains the origin of an extrinsic contribution. Our findings address, therefore, a question about the relative contribution to the remanent magnetization of bound magnetic polarons and weak ferromagnetism driven by the antisymmetric exchange interaction, the latter weakened by the formation of antiferromagnetic domains. Furthermore, we provide the theory of BMP spontaneous spin splitting, which can be probed optically.

We report the discovery of a thermodynamically stable skyrmion-antiskyrmion lattice in two-dimensional heterostructures, a novel state exhibiting a net-zero global topological charge owing to an equal population of skyrmions and antiskyrmions. This surprising coexistence of oppositely charged solitons remarkably circumvents their anticipated annihilation. We demonstrate the formation and evolution of this phase in Fe films on $C_{1v}$-symmetric (110) surfaces of GaAs and CdTe semiconductors. Specifically, we reveal a series of magnetic-field-induced phase transitions: cycloidal spin-spiral $\to$ skyrmion-antiskyrmion lattice $\to$ conical spin-spiral $\to$ ferromagnet. The remarkable stability of the net-zero lattice is attributed to symmetry-enforced anisotropic magnetic interactions. Lowering interfacial symmetry to $C_{1v}$ thus enables frustrated chiral magnets, uniquely manifesting in thermodynamically stable net-zero topological soliton lattices, as revealed by our findings.

Quantum spin chains with competing interactions offer a platform where low dimensionality and frustration—both acting to suppress magnetic order—intersect. We studied magnetic ordering in the spin-$\frac{1}{2}$ chain compound ${\mathrm{AgCuVO}}_4$ using muon spin spectroscopy and neutron diffraction. Long-range magnetic order emerges at $T_N=2.0\left(1\right)\mathrm{K}$, which is $\sim 1/200$ of the dominant intrachain coupling $J$ and $\sim 1/15$ of the interchain interactions. The collinear incommensurate amplitude-modulated magnetic structure features a reduced ordered moment of $0.13\left(3\right){\mu }_{\mathrm{B}}$, confined to the $ab$ plane and modulated along the $c$ axis—perpendicular to the spin chains—indicating frustrated interchain couplings. The low $T_N$, small moment, and incommensurate order highlight strong frustration, positioning ${\mathrm{AgCuVO}}_4$ as a model system for exploring frustration in quantum spin chains.

The controllable nonreciprocal propagation of light is an intensively investigated field of optics, with studies motivated both by fundamental questions and possible telecommunication applications. So far, polarization-independent, switchable one-way transparency has been demonstrated only at certain resonances of multiferroic crystals at cryogenic temperatures and in high magnetic fields, limiting the practical implementation of this effect. Here, as an alternative approach, we present the one-way transparency of an artificial layered structure consisting of split-ring metamaterial and magnetic substrate layers interacting in the dynamic regime. As evident from our quasioptical experiments in the GHz frequency range, this unique combination breaks time and space inversion symmetries in external magnetic field. The ease of tuning the dynamic response and the possibility of controllable one-way transparency make this approach promising for real-world applications.

We present a comprehensive theoretical study of the topological properties of triplon excitations in spin-$1/2$ dimer-singlet ground states defined on the maple-leaf and star lattices. Our analysis is based on a model that includes Heisenberg interactions, Dzyaloshinskii-Moriya (DM) interactions, and an external magnetic field. In the absence of an in-plane DM vector, we demonstrate that the triplon Hamiltonian maps onto the magnon Hamiltonian of the kagome lattice, inheriting its nontrivial topological characteristics, including Berry curvature and topological invariants such as the ${\mathbb{Z}}_2$ invariant and Chern numbers. This correspondence enables us to derive approximate analytical expressions for the spin Nernst and thermal Hall conductivities. Furthermore, we explore the effects of realistic finite in-plane DM interactions, uncovering multiple topological transitions and a complex thermal Hall conductivity behavior, including potential sign reversals as functions of magnetic field and temperature. Using layer groups, we also provide a symmetry classification of the star and maple-leaf lattices.

Charge order induced ferroelectrics display important technological applications in spintronics devices due to the possibility of magnetoelectric coupling and fast electronic switching. However, the list of known charge order induced ferroelectrics remains limited, hindering the fundamental understanding of the phenomena and the optimization of materials for real applications. In this work, we develop a high-throughput workflow to screen for charge order induced ferroelectrics in the Materials Project database. We use the local symmetry and bond valence sum to determine 147 materials displaying a coexistence of charge order and ferroelectric polarization. Then, ab initio simulations are used to identify 21 charge order induced ferroelectric candidates in which the ferroelectric polarization originates from, or is structurally coupled to, the charge order. For the final 21 candidates, we use symmetry-adapted modes and first-principles calculations to determine the structural coupling term between charge order and polar distortions and compute electronic properties, respectively.

Anisotropic magnetic exchange interactions induced by spin-orbit coupling have been less explored than their isotropic part and, when they were, they were nearly always limited to the Dzyaloshinskii-Moriya interaction (DMI) and single-site anisotropy. In our work, we address the full magnetic exchange interaction matrix using density functional theory, including all terms allowed by the crystal symmetry of Fe-based kagome metal. To this end, we propose an accurate but computationally inexpensive protocol to obtain the anisotropic magnetic exchange interactions, whereby only the spin quantization axis is rotated and other parameters remain fixed, reducing computational noise. We observe a smooth trigonometric energy dependence on the rotation angle and extract magnetic interaction parameters from the trigonometric equation fitting obtained from our mathematical expression for the Fe-based kagome metal. We also investigated how the chemical composition and crystal structure affect DMI and other anisotropic terms in the Fe-based kagome structure. Our simple protocol for robust calculations of nonzero anisotropic magnetic interactions, which naturally cancel our systematic errors, can be readily applied to other materials. In the second part, we calculate zone-center phonon frequencies and show how they depend on the presence of magnetism and on the pattern of magnetic ordering.

We propose a tunneling spin Hall effect in a normal metal/$p$-wave magnet/superconductor junction. It is found that the Andreev reflection in the normal lead is spin dependent and exhibits strong asymmetry with respect to the transverse momentum, giving rise to a pure transverse spin Hall current with zero net charge. The transverse spin conductance is analytically derived using the nonequilibrium Green's function approach, revealing that the predicted spin Hall effect is governed by the direction of the Fermi surface splitting in the $p$-wave magnet. A finite transverse spin current with a large spin Hall angle arises when the line connecting the centers of the spin-split Fermi surfaces is perpendicular to the normal direction of the junction, which indicates a highly efficient charge-to-spin conversion, suggesting potential applications in spintronic devices.