Fractional Chern insulators arise in topologically nontrivial flat bands, characterized by an integer Chern number $\mathit{C}$ that corresponds to the number of dissipationless edge states in the noninteracting regime. Higher Chern numbers can replicate the physics of higher Landau levels and often confer enhanced topological robustness. However, realizing correlated fractional phases with higher Chern numbers in such flat band systems remains challenging. Here, we propose an interlayer coupling scheme to generate higher Chern numbers in a flat-band system, where the interlayer coupling transforms two $\mathit{C}=\text{1}$ bands in a bilayer checkerboard lattice into a single flat band with $\mathit{C}=\text{2}$ by lifting their degeneracy and merging their topological indices. Exact diagonalization calculations reveal that this engineered band hosts two fractional Chern insulator states with many-body Chern numbers $\mathit{C}=2/3$ and 2/5 at fillings of $\nu =1/3$ and 1/5, respectively. An experimental setup is proposed to simulate these states using cold alkaline-earth-like atoms in an effective bilayer optical lattice. Our work provides a general and widely applicable strategy for constructing higher Chern number flat bands, opening a pathway to explore exotic fractional quantum phases.

We investigate a valleytronic method to enhance net phonon absorption by electrons (phonon valleytronics), enabling improved in situ thermoelectric cooling in heterostructured semiconductor devices. We show that electron energy filtering at a heterojunction barrier, combined with tailored valley offsets, generates a nonequilibrium carrier distribution that favors certain intervalley phonon absorption transitions. Using an analytic model and ensemble Monte Carlo simulations for thin ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ barriers, we demonstrate that this effect leads to a thermionic current sustained by phonon absorption-mediated $\mathrm{\Gamma }\to \mathrm{L}/\mathrm{X}$ transitions. With intervalley phonon harvesting, the phonon-electron conversion efficiency (coefficient of performance) increases by a factor of more than two compared with conventional solid-state thermionic energy filtering, under moderate bias at 300 K.

We theoretically investigate the three-dimensional (3D) electron dynamics of graphene in real space under strong laser fields using time-dependent density functional theory (TDDFT). We successfully reproduce the reversal of current direction originating from the cancellation of two oppositely directed residual currents, as previously predicted by [Y. Morimoto et al., New J. Phys. 24, 033051 (2022)]. By distinguishing contributions from individual orbitals, our results validate the two-level system approximation and also emphasize that the first-principles approach agrees better with experimental results for light-driven residual current, especially in extremely strong fields. Furthermore, our 3D model reveals that the real-space atomic-scale current induced by strong laser fields is concentrated slightly above and below the graphene basal plane, rather than strictly within it. The two oppositely directed currents exhibit a pronounced height separation in the out-of-plane direction, indicating that the ring current is not confined to the graphene plane but forms a rotating 3D circulation loop, which is absent in the reduced-dimensional model.

Charge Kondo circuits consist of metallic islands connected by single-mode quantum point contacts (QPCs). The island's charging energy makes these circuits tunable quantum simulators of various strongly interacting models. Here we propose a circuit that realizes the Kondo effect with effective Luttinger-liquid interactions, and show that it undergoes a localization transition in which the QPC transmission is fully suppressed below a critical value. Experimental signatures include a diverging charge susceptibility and an entropy step. Our findings open a path toward realizing localization transitions in more exotic settings.

We report nonreciprocal charge transport in epitaxial monoclinic ${\mathrm{SrIrO}}_3$ ($m$-SIO) thin films, a nonsymmorphic symmetry-protected Dirac semimetal with strong spin-orbit coupling. Second-harmonic magnetotransport measurements reveal both bilinear magnetoelectric resistance and a nonlinear planar Hall effect, providing clear evidence of spin-momentum locked states in $m$-SIO. Systematic angular-dependent measurements suggest a predominantly in-plane spin vector oriented perpendicular to the electron momentum, consistent with Rashba-type spin-momentum locking on the Fermi surface. Quantitative analysis of the bilinear magnetoelectric resistance based on a simplified Rashba model yields a large effective Rashba parameter, suggesting that the Rashba-type surface states are closely related to the strongly spin-orbit coupled electronic structure of the nonsymmorphic Dirac bulk states. Our results provide a transport route to probe Rashba-type spin-momentum locking in $m$-SIO and identify $m$-SIO as a promising platform for oxide spin-orbitronics.

We address the problem of magnetic field induced corner states in quantum spin Hall insulators beyond the particle hole symmetric limit. Starting from a realistic low-energy model for zinc-blende semiconductor quantum wells, we derive the effective edge Hamiltonian in the form of a Dirac Hamiltonian with two magnetic field dependent mass terms, whose structure depends on the crystallographic orientation of the edge and of the magnetic-field orientation. Our analytical results show that magnetic field induced corner states are most naturally understood as in-gap bound states of the effective edge theory, controlled by the relative configuration of the edge mass vectors rather than, in general, as higher-order topological corner modes protected by a stable bulk invariant. We demonstrate that, although mirror-graded winding numbers can be defined and quantized for certain crystallographic configurations, the existence of magnetic field induced corner states is not restricted to regimes in which these bulk invariants are well defined. Finally, we argue that even without higher-order topological protection these corner states may remain spectrally robust under weak perturbations as isolated in-gap quasiparticle excitations.

We present a systematic study of the evolution of the band structure in the Fe-based superconductor family ${\mathrm{BaFe}}_{2-x}{M}_x{\mathrm{As}}_2$ ($M$ = Co, Cu, Cr, Ru, and Mn) using polarization-dependent angle-resolved photoemission spectroscopy (ARPES). Low-substituted samples, with comparable spin-density wave transition temperatures ($T_{\text{SDW}}$), were chosen to enable controlled comparisons with respect to the parent compound. The sizes of the central $\alpha$ and $\beta$ hole pockets remain largely unchanged across different substitutions, while the $\gamma$ pocket exhibits no clear correlation with either $T_{\text{SDW}}$ or the As height relative to the Fe plane. The evolution of both hole and electron pockets does not follow a rigid-band shift scenario and shows no systematic dependence on the nominal electron or hole character of the substituting element. However, subtle trends are observed: a modest increase of the electron pocket with planar character that correlates with $T_{\text{SDW}}$ suppression, while its contraction appears linked to an increase in the As height relative to the Fe planes. Our results suggest that the suppression of $T_{\text{SDW}}$ is primarily driven by changes in the Fe–As bond length, with the effect being more pronounced in electronic states with planar character. These findings provide insight into the electronic structure of ${\mathrm{BaFe}}_{2-x}{M}_x{\mathrm{As}}_2$.

Inducing spin-sublattice inequivalence through correlation-driven orbital order, rather than crystallographic anisotropy, has been proposed as a route to altermagnetism (AM). However, in two-orbital systems, it is blocked by the GKA rules, which favor ferromagnetic superexchange for orderly occupied orbitals. Through first-principles calculations on ${\mathrm{KCoF}}_3$ and ${\mathrm{KNiF}}_3\text{−}{\mathrm{KCuF}}_3$ superlattice, we show that the limitation can be bypassed by employing two coupled orbital subsets that separately supply the occupation-ordered orbitals and the dominant antiferromagnetic exchange contribution, establishing a minimal orbital condition for intrinsic spin-orbital AM, and reveal the distortion-insensitive finite spin splitting in ${\mathrm{KCoF}}_3$, which is distinct from extrinsic AM induced by crystallographic anisotropy. These results clarify the microscopic mechanism of spin-orbital AM and delineate a general route for realizing unconventional magnetism in correlated materials.

There is a close theoretical connection between topological Floquet physics and cavity quantum electrodynamics (QED), yet this connection has not been realized experimentally due to complicated cavity QED models that often arise. We propose a simple, experimentally viable protocol to realize nonadiabatic topological photon pumping mediated by a single qubit, which we dub the anomalous Floquet photon pump. For both quantized photons and external drive, the system exhibits a nontrivial topological phase across a broad range of parameter space. Transitions out of the topological phase result from frequency-space delocalization. Finally, we argue that the protocol can be implemented in existing experiments via driven qubit nonlinearities, with topological pumping witnessed in reconstruction of the cavity Wigner distribution functions.

Accurate simulations of the Hubbard model are crucial to understanding strongly correlated phenomena, in which small energy differences between competing orders demand high numerical precision. In this work, neural quantum states are used to probe the strongly coupled and underdoped regime of the square-lattice Hubbard model. We systematically compare the hidden fermion determinant state and the Jastrow-Backflow Ansatz, parametrized by a vision transformer, finding that in practice, their accuracies are similar. We also test different symmetrization strategies, finding that output averaging yields the lowest energies, although it becomes costly for larger system sizes. On cylindrical systems, we consistently observe filled stripes. On the torus, our calculations display features consistent with a doped Mott insulator, including antiferromagnetic correlations and suppressed density fluctuations. Our results demonstrate both the promise and current challenges of neural quantum states for correlated fermions.

Among the extensive studies of fractional quantum anomalous Hall (FQAH) states, there recently has appeared a growing interest in the topological states with coexisting charge density wave (CDW) orders. Such states are referred to as Hall crystals. However, compared to those with integer Hall conductivities, the FQAH crystal (FQAHC) is still elusive, even at the level of a microscopic model. In this work, we numerically study a topological flat-band model on a triangular lattice with spinless fermions. At fractional filling of the Chern band, the nearest-neighbor interaction leads to a commensurate and topologically trivial CDW state. Interestingly, the folded miniband above the CDW gap is nontrivial, and we focus on the doping of it without any projection. A series of (F)QAHC states at (fractional) integer fillings of this miniband is discovered and some FQAHC state might even exist in less “ideal” conditions. The ground-state degeneracies of such (F)QAHC states are enlarged by the CDW degeneracy, and the Hall conductivities—determined by the fillings of the miniband—are different from the fillings of the original Chern band. We also study the thermodynamics of an FQAHC state and find a compressible CDW phase at intermediate temperatures, which might serve as a precursor of a lower-temperature FQAHC phase. Moreover, we numerically demonstrate that such a generic scheme of doping a CDW-folded topological miniband could be applied to bosonic systems, broadening the platforms of Hall-crystal physics and motivating its exploration in quantum moiré and cold-atom systems.

In strongly correlated transition metal dichalcogenides, an intricate interplay of polaronic distortions, stacking arrangement, and electronic correlations determines the nature of the insulating state. Transient changes in pristine and Mo-doped $1T\text{−}{\mathrm{TaS}}_2$ are measured by femtosecond time-resolved photoelectron spectroscopy and modeled using nonequilibrium dynamical mean-field theory complemented by density functional theory. Inspired by vibrational spectroscopy we analyze real-time oscillatory spectral changes induced by the charge density wave amplitude mode through modulations of electronic interactions. We distinguish effects induced by electron doping and structural disorder which can modify the layer stacking and conclude that doped crystals might feature an enhanced fraction of monolayers. Our work establishes substitutional doping as a pathway to engineer the dynamic electronic structure in correlated transition metal dichalcogenides.

Long-lived spin-helix states facilitate the study of nonequilibrium dynamics in quantum magnets. We consider the decay of transverse spin helices in antiferromagnetic spin-$S$ XXZ chains with single-ion anisostropy. The spin-helix decay is observable in the time evolution of the local magnetization that we calculate numerically for the system in the thermodynamic limit using infinite time-evolving block decimation simulations. Although the single-ion anisotropy prevents helix states from being eigenstates of the Hamiltonian, they still can be long-lived for appropriately chosen wave numbers. In the case of easy-axis exchange anisotropy, the single-ion anisotropy may even stabilize the helices. Within a spin-wave approximation, we obtain a condition giving an estimate for the most stable wave number $Q$ that agrees qualitatively with our numerical results.

In this work, we investigate the interaction between the tip of an atomic force microscope and single Ho and Gd adatoms adsorbed on Cu(111). Force-distance spectroscopy shows a pronounced long-range repulsive force that dominates at tip-sample separations larger than 700 pm and precedes the onset of measurable van der Waals attraction. In constant-height imaging, this interaction gives rise to a characteristic ring-shaped contrast. The measured force-distance curves and image features are quantitatively reproduced by a model that only includes electrostatic, van der Waals, and Pauli terms. Measurements performed with CO-terminated and bare metal tips show that the long-range repulsion is governed primarily by the electrostatic interaction between the dipole moment of the metallic tip apex and the adatom. Comparison with Fe adatoms demonstrates that the observed long-range rings are distinct from short-range chemical contrast.

We systematically investigate the magneto-optical transport and the associated Faraday and Kerr rotations in 8-Pmmn monolayer borophene subjected to a perpendicular magnetic field and off-resonant Floquet driving. The interplay between Floquet band engineering, Landau quantization, and optical selection rules leads to distinct features in the magneto-optical response. In particular, the real part of the longitudinal magneto-optical conductivity exhibits a series of resonance peaks arising from optically allowed intra- and inter-Landau-level transitions, whereas the Hall conductivity is dominated by a single pronounced resonance peak associated with the lowest cyclotron-like transition. Consistently, the complex reflectivity spectra for right- and left-circularly polarized light display analogous structures: their real parts contain multiple resonant peaks reflecting the longitudinal response, while their imaginary parts show a single dominant resonance peak with opposite phases originating from the Hall contribution. As a consequence of the resulting circular birefringence and dichroism, the Faraday and Kerr rotation angles exhibit similar resonance characters but opposite spectral phases, reflecting the different electromagnetic boundary conditions of transmission and reflection geometries. These findings indicate that the combined effects of magnetic-field-induced Landau quantization and Floquet band engineering provide an efficient pathway to control magneto-optical responses in borophene, revealing its potential for tunable two-dimensional magneto-optical and optoelectronic devices.

Altermagnets (AMs) are an emergent class of magnetic materials that combine properties of ferromagnets and antiferromagnets, exhibiting spin-polarized Fermi surfaces and zero net magnetic moment due to combined time-reversal and crystal symmetry. Here, we construct a Kondo-lattice model on a two-dimensional (2D) square Lieb lattice to investigate the topological properties of AMs. We identify a type-II quantum spin Hall state characterized by spin-polarized counterpropagating edge states. Breaking the $C_{4z}\mathcal{T}$ symmetry, which connects magnetic sublattices, induces a transition to a quantum anomalous Hall state. We further establish a strain-induced mechanism to control these topological phase transitions and present the corresponding phase diagram. Finally, we demonstrate the predicted transitions in monolayer CrO, a realistic altermagnetic candidate, using first-principles calculations. Our findings highlight the potential of 2D AMs as a versatile platform for topological spintronics, enabling strain-tunable helical and chiral edge states within a single system.

We introduce a linear-scaling real-space methodology to compute time-resolved electrical responses of materials driven far from equilibrium, with energy relaxation and disorder treated on an equal footing. Applying this approach to gapped monolayer and AB-stacked (Bernal) bilayer graphene, when driven by a circularly polarized optical pulse, we observe the generation (suppression) of a finite Hall conductivity when the system is trivial (topological). This Hall signal oscillates during optical driving and remains sizable after the light is switched off before relaxing toward equilibrium. Remarkably, this dynamical Hall response is robust in the presence of realistic descriptions of disorder, suggesting that disorder and relaxation dynamics can be leveraged as design parameters rather than as limitations. More broadly, our new methodology enables the investigation of electrical responses in driven, complex disordered quantum materials and highlights how engineered energy-transfer pathways can enable ultrafast optoelectronic functionality.

The valley degree of freedom in tetragonal systems, governed by crystalline symmetry rather than time-reversal symmetry, offers a distinct paradigm for valleytronics compared to hexagonal systems. Combining symmetry-adapted tight-binding and first-principles calculations, we investigate strain-engineered valley physics in tetragonal monolayers featuring ${\mathit{C}}_{4z}$ and ${\mathit{S}}_{4z}$ symmetries. We unveil that the intrinsic valley-layer coupling within ${\mathit{S}}_{4z}$ symmetric systems, together with a giant bipolar out-of-plane piezoelectric response, enables significant and reversible valley polarization under bipolar in-plane uniaxial strain in the ${\text{Hf}}_2{\text{SiCO}}_2$ monolayer. This phenomenon arises from the interplay between strain-modified hopping integrals and the resulting crystal field potential, distinguishing it from traditional electric-field-driven mechanisms. Furthermore, the symmetry-allowed valley-contrasting linear dichroism under applied strain is notably robust. Our findings highlight strain-direction selectivity as a powerful strategy for achieving and controlling valley polarization, providing a general theoretical framework for mechanovalleytronics in tetragonal systems.