This work examines a mobile impurity interacting with a bath of a few spin-$\uparrow$ and spin-$\downarrow$ fermions in a small one-dimensional open lattice system. We study ground-state properties using the exact diagonalization method, where the system is modeled by a three-component Fermi Hubbard Hamiltonian. We find that in addition to the standard phase separation between a strongly repulsive impurity and the bath, a strongly attractive impurity also phase separates with the fermionic holes due to the particle-hole symmetry. Furthermore, we find that the impurity can show an oscillatory pattern in its density for intermediate attractive and repulsive bath-impurity interactions, which are induced by Friedel oscillations in the finite-size fermionic bath. This rich behavior of the impurity could be probed with fermionic ultracold mixtures in optical lattices.

The physical origin of third harmonic magnetoresistance remains debated in nonlinear spintronics. Here we systematically study third harmonic magnetoresistance in Ni-based films with different in-plane anisotropies, including polycrystalline Ni and epitaxial Ni(001) systems. Using in-plane field-rotation measurements together with magnetic-field scaling, we identify thermal anisotropy modulation as a dominant mechanism, distinct from the conventional thermal magnetization modulation. ac Joule heating induces periodic temperature oscillations that modulate magnetic anisotropy constants, driving coherent magnetization oscillations. This mechanism produces distinct angular fingerprints, such as a characteristic sixfold symmetry in Ni(001) films with fourfold magnetic anisotropy. By establishing a quantitative framework based on the $1/H$ and $1/H^2$ scaling relations, we effectively decouple the thermal contributions arising from current-induced modulations of uniaxial and fourfold magnetic anisotropies. Our findings provide a rigorous methodology for interpreting higher-order harmonic transport and highlight thermal-anisotropy coupling as an essential ingredient in nonlinear spintronic measurements.

The finite mass of a skyrmion in a ferrimagnet, which is determined by the exchange interaction between spins belonging to different ferrimagnetic sublattices, leads to a gyroscopic motion of skyrmions, which is conceptually similar to the electron cyclotron resonance (ECR) in metals. We show that it can be excited in a ferrimagnetic film by a spin current or microwaves. Similar to how the ECR permits measurement of the effective electron mass, the skyrmion cyclotron resonance (SCR) must permit unambiguous measurement of the skyrmion mass. The presence of massive skyrmions strongly influences the spectrum of spin excitations in a ferrimagnet. The dependence of the SCR frequency on parameters is computed for a TM/RE (transition-metal/rare-earth) ferrimagnet, using CoGd as an example. The cyclotron frequency exhibits a dip near angular momentum compensation, where it hybridizes with the ferromagnetic resonance. The skyrmion cyclotron mode is studied for individual skyrmions and for skyrmion lattices, where the effect must be strong enough to be observed in microwave and spin-current experiments.

We develop a unified theory of nonadiabatic wave-packet dynamics for Bloch electrons subject to slowly varying spatial and temporal perturbations. Extending the conventional wave-packet ansatz to include interband contributions, we derive the equation governing the interband coefficients from the time-dependent variational principle and refer to it as the wave-packet coefficient equation. Near the adiabatic regime, we can integrate out the small interband amplitudes to obtain the leading nonadiabatic corrections to the effective wave-packet Lagrangian. These corrections take three forms: (i) a nonadiabatic metric in real and momentum space, which in two-band models reduces to an energy-gap-renormalized quantum metric; (ii) gauge-invariant corrections to the Berry connections governing the motion of the wave-packet center; and (iii) an energy correction induced by spatial and temporal variations of the Hamiltonian. When the nonadiabatic metric is invertible, the dynamics can be recast as forced geodesic motion in phase space, providing a restricted gravitational analogy for Bloch-electron dynamics. As an illustration, we apply the formalism to one-dimensional Dirac electrons coupled to a slowly varying exchange field.

The existence of an elementary magnetic pole (charge) was predicted by Dirac in 1931 and here we propose and implement semiconductor nanostructures supporting such poles, which are InN/GaN heterostructure nanowires (NWs) with a few monolayer thick InN inclusions, grown using plasma-assisted molecular beam epitaxy. The formation of magnetic pole/charge occurs in this NWs due to piezoelectric effect leading to formation of Wigner quantum dots (WQDs) having magnetoelectron states—Dirac anyons (DAs), created by magnetic flux quanta self-generated in single-particle states, previously observed in self-assembled InP/${\mathrm{GaInP}}_2$ WQDs [Mintairov et al., Phys. Rev. B 111, 045410 (2025)]. The formation of WQDs and DAs/magnetic poles having intrinsic magnetic field of several tens of Tesla is evident from the multipeak structure and up to 100% of circular polarization degree of the photoluminescence spectra measured for single NWs. This is supported by the calculations of single-particle states using $\overline{k}·\overline{p}$ model and electron density distributions using the configurational interaction approach. The presented results demonstrate the scaling of magnetic pole/Dirac anyon properties with material parameters, which allows the realization of high-temperature magnetic pole structures that can be used in nanophotonics and topological quantum computing applications.

We investigate the optical properties of neutral excitons in CdTe/ZnTe quantum dots containing a single ${\mathrm{Ni}}^{2+}$ ion. We show that the photoluminescence spectra provide a direct spectroscopic signature of strain-induced mixing of the ${\mathrm{Ni}}^{2+}$ spin states. A misalignment between the principal axis of the local strain tensor and the quantum dot growth direction reorients the spin quantization axis of the magnetic ion, reducing the $\mathrm{hole}\text{−}{\mathrm{Ni}}^{2+}$ exchange interaction at low magnetic field and giving rise to photoluminescence replicas around the partially linearly polarized bright-exciton transitions. A longitudinal magnetic field restores the circularly polarized optical selection rules, allowing the three spin projections $S_z=0,\pm 1$ of the ${\mathrm{Ni}}^{2+}$ ion to be spectrally resolved. Dark-exciton emission appears on the low-energy side of the spectra and is dominated at low field by transitions involving spin flips of the magnetic ion. An effective spin Hamiltonian including strain orientation and valence-band mixing reproduces the magnetic-field evolution of both bright- and dark-exciton spectra. These results highlight the key role of the local strain environment in determining the spin-exciton coupling of transition-metal dopants in semiconductor quantum dots.

The work functions of ${}^7\mathrm{Li}$ and ${}^6\mathrm{Li}$ metals have been measured as a function of temperature, by using photoionization of pure isolated metal nanoparticles in a beam. These data reveal a marked isotope effect in the temperature variation of these work functions. Furthermore, for both isotopes the curvature of this temperature variation is found to be significantly larger than may be ascribed purely to a change in the electron-gas density. These findings enhance the characterization of lithium as a quantum material in which the interplay between electronic and ionic degrees of freedom is nontrivial, and call for a microscopic understanding beyond simple models. Additionally, the slope of the work-function curves was observed to vanish in the low-temperature limit, as had been predicted on the basis of the Third Law of Thermodynamics.

We report an advanced formulation of the Fourier modal method developed for two-dimensionally periodic multilayered structures containing materials with nonzero macroscopic magnetoelectric coefficients (also known as coefficients of chirality and bianisotropy) represented as arbitrary $3\times 3$ tensors. We consider two numerical schemes for this formulation: with and without generalized Fourier factorization rules. For both schemes, we provide explicit expressions for the Fourier tensors of macroscopic material parameters and demonstrate that, in the absence of magnetoelectric coupling, they reduce to the conventional factorization rules. We show that the scheme employing factorization rules facilitates improved convergence, even when the macroscopic chirality coefficient is large. The described formulation represents a fast and rigorous technique for theoretical studies of periodic structures with chiral, bianisotropic, or nonreciprocal materials in the widely used framework of the Fourier modal method.

Two-dimensional Janus materials, characterized by their inherent structural asymmetry, provide an ideal platform for coupling magnetism with valleytronic properties. Herein, we propose two hydrogenated Janus monolayers, GdISeH and GdITeH, based on experimental layered ${\mathrm{GdI}}_2$, which leverage the strong spin-orbit coupling of gadolinium. Their structural, magnetic, electronic, and valleytronic properties are systematically investigated using first-principles calculations, Monte Carlo simulations, and Wannier function analysis. Both monolayers exhibit a ferromagnetic ground state with in-plane magnetic anisotropy (IMA) and high Curie temperatures of 216 K for GdISeH and 190 K for GdITeH. When magnetized out of plane, they exhibit substantial valley polarization (163 meV for GdISeH and 196 meV for GdITeH) along with prominent valley-contrasting Berry curvature, satisfying the key requirements for the anomalous valley Hall effect (AVHE). The electronic states are highly tunable: biaxial strain drives phase transitions among bipolar magnetic semiconductor (BMSC), bipolar magnetic semimetal (BMSM), and unipolar magnetic semiconductor (UMSC) phases, while carrier doping induces switching between BMSC and half-metal (HM) states. Notably, a low concentration of hole doping (below approximately 0.02 $h$/f.u. for GdISeH and slightly above this for GdITeH) switches the magnetic anisotropy from IMA to perpendicular magnetic anisotropy, which is essential for stabilizing valley polarization and realizing the AVHE. The high-temperature ferromagnetism, large valley polarization, AVHE, as well as versatile BMSC, BMSM, UMSC, and HM characteristics with high spin polarization make Janus GdISeH and GdITeH monolayers promising candidates for spintronic and valleytronic applications.

We consider a half-filled two-dimensional Su-Schrieffer-Heeger lattice and examine the role of the long-range Coulomb electron-hole attractive interaction. We demonstrate that under specific conditions, a rare interplay of topological and excitonic-collective behavior emerges as a novel state of matter. A unique Bose-Einstein condensate of excitons forms, exhibiting the co-presence of pseudospin chiral texture. The emerging complex order parameter, a particle-hole pairing gap, has nonzero real and imaginary parts throughout the Brillouin zone (BZ) but vanish separately on two different nodal lines, which intersect at two Weyl points. The Weyl nodes possess opposite pseudospin chiralities, which act as source and drain of a Berry flux associated with the particle-hole pairing wave function, and are the cause of Bogoliubov–de Gennes Fermi-arc edge states. We self-consistently calculate the full momentum dependence of the particle-hole pairing gap throughout the entire BZ. Near the Weyl points, the pairing gap exhibits the unconventional $p_x+i{p}_y$ character. Finally, we discuss general potential experimental realizations of this novel state of matter.

Multiexciton states in monolayer transition metal dichalcogenides represent fertile ground for uncovering emergent many-body quantum behaviors, particularly in the context of valley polarization and coherence. Understanding how complex excitonic correlations influence valley-resolved optical properties is essential for both fundamental valleytronic science and potential quantum applications. Here, we investigate the valley-selective polarization characteristics of hexcitons—six-body bound states—in monolayer ${\mathrm{WSe}}_2$. Surprisingly, we observe that hexciton photoluminescence exhibits strong circular polarization but negligible linear polarization, indicating that valley polarization is well preserved, while valley coherence is entirely lost. This decoupling behavior stands in stark contrast to neutral excitons, which typically exhibit both forms of polarization, and points to fundamentally different valley dynamics in higher-order excitonic complexes. Our analysis reveals that, despite nominally symmetric excitation and emission configurations at the +$K$ and $-K$ valleys, the exchange interactions and spins in the many-body final states subtly break the conditions required for intervalley coherence, suppressing any linear polarization signature. These findings shed light on the intrinsic decoherence mechanisms in multiexciton systems and highlight the critical role of many-body effects in shaping the valley quantum dynamics of two-dimensional semiconductors.

The transition from order to disorder is conventionally regarded as detrimental to solid-state heat transfer in classical wave and quasiparticle systems. In striking contrast, we show that in near-field thermal radiation, breaking long-range order—shifting from periodic to quasiperiodic configurations—induces a counterintuitive enhancement of energy transport. When the transmission structure transitions from a conventional periodic photonic crystal to a quasiperiodic Fibonacci geometry, the radiative heat flux can increase by more than an order of magnitude. This effect arises from delocalized interactions within quasiperiodic elements, where quasiperiodicity relays and amplifies thermal electromagnetic energy transfer across large spatial separations, surpassing even corresponding near-field scenarios. The extraordinary transport properties induced by quasidisorder in near-field thermal radiation could open possibilities for heat-flow manipulation, offering transformative implications for thermal science and advancing the fundamental understanding of collective excitations in non-ordered systems.

Altermagnets are a recently discovered class of compensated magnets with momentum-dependent spin splittings and unusual transport properties, even without a net magnetization. In the presence of combined fourfold rotation and time-reversal ($C_4\mathcal{T}$) symmetry, linear and also second order, driven by a Berry curvature dipole, anomalous Hall responses are forbidden in any pure $d$-wave altermagnet. Nevertheless, here we find that the nontrivial quantum metric of the occupied Bloch states allows for an electric field induced Berry curvature dipole, which generates a strong and tunable second-order Hall current, enabling it to be switched on or off by simply adjusting the relative orientation between the symmetry-reducing dc field and the ac probe field. Specifically, we investigate the electric field induced second-order anomalous Hall response in a two-dimensional Rashba-coupled altermagnet with varying $d_{x^2-y^2}$ ($B_{1g}$) and $d_{xy}$ ($B_{2g}$) altermagnet symmetry to capture all possibilities. Crucially, the nonlinear signal is highly sensitive to the underlying symmetry of the altermagnetic order at specific doping levels, offering a purely electrical method to distinguish distinct altermagnetic orders. Our results position altermagnets as a promising platform for controllable nonlinear transport and spintronic applications.

We determine the magnetic ground state of the kagome lattice magnet ${\mathrm{Nd}}_3{\mathrm{Ru}}_4{\mathrm{Al}}_{12}$ by single-crystal neutron diffraction, supported by experiments with polarized neutrons. We identify this material as a collinear ferromagnet (“hex-FM”) with uniform moment length and ordering vector $\mathit{Q}=0$, in contrast to a previous, seminal report that proposed unequal moment lengths on two Nd sites, here called the “ortho-FM” state. Our analysis of the flipping ratio in polarized neutron scattering is consistent with the hex-FM state. The results provide a microscopic basis for understanding the large fluctuation-induced Hall and Nernst responses near $T_{\mathrm{C}}\approx 41\mathrm{K}$, as previously reported for ${\mathrm{Nd}}_3{\mathrm{Ru}}_4{\mathrm{Al}}_{12}$.

It is shown that in all types of metallic magnets, the coupling of the order parameter to the conduction electrons leads to an order-parameter susceptibility that is long-ranged at zero temperature. This is true for all known classes of ferromagnets, and also for antiferromagnets and spin-density wave systems, helimagnets, magnetic nematics, and altermagnets. The consequences for the magnetic quantum phase transition vary between different classes of magnets. In almost all three-dimensional (3-d) systems with a homogeneous magnetization, as well as in magnetic nematics and in altermagnets, the long-ranged correlations generically modify the nature of the magnetic quantum phase transition from second order to first order. The only exceptions are noncentrosymmetric ferromagnets with a strong spin-orbit interaction, where the correlations change the order of the transition in two-dimensional systems, but not in 3-d ones. In helimagnets, spin-wave systems, and Néel antiferromagnets, their effect is even weaker and does not change the order of the transition if the ordering wave number is sufficiently large, except in flat-band systems. In systems with quenched disorder, the transition generically is of second order, but the correlations modify the critical behavior. These conclusions are reached by very simple considerations that are based entirely on the single-particle excitations in the nonmagnetic phase and their modifications by a field conjugate to the order parameter, augmented by renormalization-group considerations.

Recently, a high-efficiency thermoelectric candidate SnSe has been experimentally shown to undergo a phase transition induced by femtosecond laser excitation, but the underlying microscopic mechanism has not been fully clarified. Photoinduced phase transitions provide an effective means to disentangle electronic and lattice interactions on ultrafast timescales. Using real-time time-dependent density functional theory combined with occupation-constrained density functional theory methods, we investigate the structural response of SnSe under the excitation of 800 nm ($\hslash \omega =1.55\mathrm{eV}$). While the thermal fluctuations fail to destabilize the Pnma phase, promoting 5.4% of the valence electrons induces a rapid Pnma phase to Immm phase transformation. It is found that photoexcitation can reshape the potential-energy surface from hill-like to well-like and drive directional atomic motion. The dynamics are governed by several coherent phonon modes, such as the ${\mathrm{A}}_g^{\left(1\right)}$ and ${\mathrm{A}}_g^{\left(2\right)}$ modes, which play the dominant role in the phase transition. The transition process can be completed on a subpicosecond timescale, highlighting a carrier-driven, nonthermal mechanism for ultrafast phase control in SnSe. These findings offer valuable insights into regulating the phase behavior of SnSe-based systems under nonequilibrium conditions.

We show how combining a discrete symmetry with topological Hilbert space fragmentation can give rise to exponentially many topologically stable qubits protected by a single discrete symmetry. We illustrate this explicitly with the example of the ${\mathrm{CZ}}_p$ model, where the encoded qubits are prethermally stable to arbitrary symmetry-respecting perturbations for parametrically long times, substantially enhancing the robustness of a recently proposed construction based on nontopological fragmentation. In this model, the encoded qubits naturally come in pairs for which a universal set of transversal logical gates can be performed, ruling out (by the Eastin-Knill theorem) the possibility of using them for quantum error correction. We also comment on the combination of symmetry enrichment and topological fragmentation more generally, and the implications for use of systems exhibiting Hilbert space fragmentation as quantum memories.

We study the spin dynamics in the quasi-2D spin-$1/2$ dimer compound ${\mathrm{Ba}}_2{\mathrm{CuSi}}_2{\mathrm{O}}_6{\mathrm{Cl}}_2$, which exhibits a magnetic field-induced Bose-Einstein condensate (BEC) of triplons. Using nuclear magnetic resonance spin-lattice relaxation rate ($T_1^{-1}$) measurements combined with large-scale quantum Monte Carlo (QMC) simulations, we investigate critical fluctuations across the field-temperature phase diagram. Bridging the behavior observed in 1D and 3D systems, the $T_1^{-1}$ relaxation rate shows a pronounced peak extending well above the Néel temperature $T_N$, indicating strong two-dimensional Berezinskii-Kosterlitz-Thouless (BKT)-type fluctuations. A quantitative match between experimental and theoretical BEC phase boundaries validates an effective XXZ model. The study determines the intrinsic BKT transition temperature $T_{\text{BKT}}$ from QMC, revealing a nearly field-independent $T_{\mathrm{BKT}}/T_N\approx 0.74$. Scaling analysis of the relaxation rate shows critical exponents consistent with 2D universality, and a narrow temperature window is identified where 2D physics dominates. These findings establish ${\mathrm{Ba}}_2{\mathrm{CuSi}}_2{\mathrm{O}}_6{\mathrm{Cl}}_2$ as a model system for exploring BKT dynamics in quantum magnets.

Interfacial symmetry breaking leading to the preferential orbital occupation in complex oxide heterostructures offer effective routes to tailor magnetic anisotropy. We demonstrate the modulation of magnetic anisotropy in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ (LSMO) thin films interfaced with the infinite-layer cuprate ${\mathrm{SrCuO}}_2$ (SCO). Static magnetization measurements show a pronounced in-plane magnetic anisotropy in LSMO/SCO bilayers compared to bare LSMO films, consistent with shifts in the resonance field as a function of the angle in ferromagnetic resonance measurements. In addition, a more than two-fold increase in the Gilbert damping is observed across all LSMO/SCO bilayers relative to the bare LSMO films, further supporting the interfacial modification of magnetic anisotropy and magnetization dynamics. However, inserting a thin ${\mathrm{SrTiO}}_3$ (STO) spacer in the control LSMO/STO/SCO sample exhibits the magnetic response similar to that of bare LSMO. This underscores the key role of the LSMO/SCO interface in the observed enhanced magnetic anisotropy. First-principles density functional theory calculations reveal a relatively larger occupation of the $3d_{x^2-y^2}$ orbital near the Fermi level in LSMO/SCO, accounting for the enhanced in-plane magnetic anisotropy, while ruling out the possibility of Rashba field-induced change in magnetic anisotropy. This work provides a comprehensive understanding of enhanced in-plane magnetic anisotropy and magnetization dynamics in the nonisostructural LSMO/SCO heterostructure.