While Floquet engineering offers a powerful paradigm for manipulating topological phases, particularly Floquet Weyl semimetals, establishing an experimentally feasible strategy for tracking the dynamic evolution of such states remains a significant challenge. Here, we propose that the anomalous Hall effect, as a sensitive, all-electrical probe, can be used to track Floquet Weyl nodes. Using first-principles calculations and symmetry analysis on the quasi-one-dimensional material $\beta \text{−}{\mathrm{Bi}}_4{\mathrm{I}}_4$, we demonstrate that circularly polarized light breaks time-reversal symmetry, driving the system from a trivial insulator into a Floquet Weyl semimetal phase characterized by a nonzero Berry curvature flux. Crucially, by continuously tuning the polarization phase $\phi$ of the driving field, we show that the trajectory of the induced Weyl nodes is highly controllable, leading to their migration and eventual annihilation at high-symmetry points. We reveal that the anomalous Hall conductivity maps directly onto this topological evolution, serving as a definitive fingerprint for the generation and dynamics of Weyl nodes.

In recent years, the planar Hall effect (PHE) has become a key probe of Berry curvature and the anomalous Hall effect (AHE). Threefold-symmetric signals under in-plane fields are often attributed to such quantum mechanisms. Here, we establish a purely classical origin for a threefold-symmetric PHE. The idea is simple yet decisive: a third-order expansion of the Boltzmann equation in the magnetic field reveals that the threefold component originates from the relative positions of the mirror planes in the crystals with respect to the measurement setups. Remarkably, the threefold contribution should be ubiquitous because this symmetry condition can be realized across a broad range of crystals. Numerical estimates based on concrete models further show that its amplitude is comparable to that expected from the AHE.

New single-layer nickelate oxychalcogenides $\mathrm{B}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_2\mathrm{C}{\mathrm{u}}_2{X}_2$ ($X=\mathrm{S}$ and Se) were successfully synthesized by using a high-pressure high-temperature method. They crystallize into the tetragonal space group $I4$/mmm with alternating $\mathrm{Ni}{\mathrm{O}}_2$ square planar and $\mathrm{C}{\mathrm{u}}_2\mathrm{S}{\mathrm{e}}_2$ antifluorite layers along the $c$ direction. High-pressure synchrotron x-ray diffraction manifests that the $\mathrm{B}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_2\mathrm{C}{\mathrm{u}}_2\mathrm{S}{\mathrm{e}}_2$ can be fairly compressed along the $c$ direction, whereas the $ab$ plane is quite rigid, corresponding to its layered feature. The valence states of $\mathrm{N}{\mathrm{i}}^{2+}$ and $\mathrm{C}{\mathrm{u}}^{1+}$ were validated from both bond valence sums and x-ray absorption spectroscopy. The magnetization of $\mathrm{B}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_2\mathrm{C}{\mathrm{u}}_2{\mathrm{S}}_2$ follows the Curie-Weiss law, whereas a spin-glass-like behavior emerges below $T_{\mathrm{sg}}=5$ K. On the other hand, $\mathrm{B}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_2\mathrm{C}{\mathrm{u}}_2\mathrm{S}{\mathrm{e}}_2$ experiences a low-dimensional antiferromagnetic transition at $T_{\mathrm{N}}=200$ K. The resistivity of both compounds follows the thermal activation model at elevated temperatures and follows the three-dimensional variable-range hopping model at low temperatures, indicating the semiconducting or insulating nature. DFT+$U$ calculations indicate that weak antiferromagnetic coupling in the $\mathrm{Ni}{\mathrm{O}}_2$ layer suppresses the Fermi surface, thereby opening a gap in the electronic structure. The electrical resistance gradually decreases under high pressure, no superconductivity was observed up to 21.4 GPa. This work provides an insight to explore new layered nickelates with emergent physical properties and potential superconductivity.

The undoped Kondo necklace in 1D is a paradigmatic and well understood model of a Kondo insulator. This work performs the first large-scale study of the 1D Anderson lattice underlying the Kondo necklace with quasiexact numerical methods, comparing this with the perturbative effective 1D Kondo necklace model derived from the former. This study is based on an exact mapping of the Anderson model to one of a superconducting pairing layer connected to a metallic reservoir, which is valid in arbitrary spatial dimensions, thereby linking the previously disparate areas of reservoir-enhanced superconductivity, following Kivelson's pioneering proposals, and that of periodic Kondo systems. Our work reveals that below the lengthscales on which the insulating state sets in, which can be very large, superconducting and density-density correlations are degenerate and may both appear to approach an almost ordered state, to a degree that far exceeds that of any isolated 1D pairing layer with short-range interactions. We trace these effects to the effective extended-range coupling that the metallic layer mediates within the pairing layer. These results translate directly to the appearance of near-long-range magnetic order at intermediate scales in the Kondo systems, and explain the strong renormalization of the RKKYcoupling that we effectively observe, in terms of the back-action of the pairing layer onto the metallic layer. The effects we predict could be tested either by local probes of quasi1D heavy fermion compounds such as ${\mathrm{CeCo}}_2{\mathrm{Ga}}_8$, in engineered chains of adatoms or in ultracold atomic gases.

Experimentally, hafnia (${\mathrm{HfO}}_2$) has shown a complicated structural configuration space with various metastable phases that are not present in the equilibrium phase diagram. This leads not only to the ferroelectric orthorhombic phase with promising applications, but also to various nonpolar phases that suggest complicated phase transitions and polarization switching paths. To date, the structural configuration space is still not fully explored. In this study, we perform first-principles quantum chemically based searches and identify two alternate nonpolar phases of ${\mathrm{HfO}}_2$, which can be achieved through atomic plane shifts from high-symmetry cubic or tetragonal phases. The metastable phases have lower energy than the tetragonal phase which is commonly believed to be an intermediate state of polarization switching. These phases imply different polarization switching paths with lower barriers and coercive fields for polarization switching in hafnia.

We present a full thermodynamic description of a magnetic impurity at the edge of a superconducting wire. We find that, depending on the relative strengths of the impurity and the superconducting bulk couplings, the impurity exhibits four phases: Kondo, Yu-Shiba-Rusinov (YSR) I and II, and local moment. This rich phase diagram is due to the competition between the Kondo effect and superconductivity, and contrary to the expectation that the effects of impurities in gapped hosts are inconsequential, this phase diagram is richer than in the gapless case. We derive the impurity contribution to free energy $F_{\mathrm{imp}}\left(T\right)$ and entropy in each phase: in Kondo phase, the entropy flows monotonically from $ln2$ (ultraviolet) to 0 (infrared) with critical exponents same as that of the conventional Kondo model; in YSR phases, thermal activation of a midgap bound state produces entropy overshoots above $ln2$, saturating to $ln2$ at high $T$, and approaching either 0 or $ln2$ at low $T$ depending on whether impurity is screened or not; in the local-moment phase the impurity remains effectively decoupled, with entropy near $ln2$, with some intermediate-temperature features that progressively fade as the bulk interaction increases. These behaviors, including the entropy overshoots in the YSR and local-moment phases, stem from a splitting of the Hilbert space into distinct excitation towers: one in the Kondo phase, two in YSR I, and three in YSR II and the local-moment phase. Resolving these tower structures and thereby going beyond conventional thermodynamic Bethe ansatz yields closed-form analytic expressions for the impurity contribution to the free energy and entropy across the entire phase diagram.

We use a concerted theory-experiment effort to investigate the formation of chiral real space spin texture when the archetypal Dirac semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ is interfaced with ${\mathrm{In}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$, a ferromagnetic semiconductor with perpendicular magnetic anisotropy. We combine density functional theory calculations, linear response theory for spin susceptibility and micromagnetic simulations to explore the possibility of chiral spin texture in this heterostructure. While a nonzero off-diagonal spin susceptibility in the ${\mathrm{Cd}}_3{\mathrm{As}}_2$ layer due to inversion symmetry breaking suggests the presence of Dzyaloshinskii-Moriya interaction (DMI) between local moments in the InMnAs layers, the amplitude may not be strong enough to give a “full” skyrmion texture. Instead, the interface states at the junction may promote a “partial” skyrmion texture. Using electrical magnetoresistance measurements at low temperature, we observe an emergent excess contribution to the transverse magnetoresistance whose behavior is consistent with a topological Hall effect arising from the formation of an interfacial chiral spin texture. This excess Hall voltage varies with gate voltage, indicating a promising electrostatically tunable platform for understanding the interplay between the helical momentum space states of a Dirac semimetal and chiral real-space spin textures in a ferromagnet.

Perturbations in moiré materials, such as due to substrates or strain, are common in many experiments and can significantly modify the electronic properties of the system. Here, we show that perturbations in twisted bilayer graphene tend to be transferred between the coupled Dirac cones, eventually reaching an equilibrium near the magic angle. We connect our results to experiments and show that this equilibrium behavior remains robust even when the moiré potential itself is perturbed. Our findings extend the notion of the magic angle to a more general regime governed by moiré-driven equilibrium.

Identifying whether a many-body ground state is gapped or gapless is a fundamental yet challenging problem, especially in quantum spin liquids. In this work, we develop a gap-diagnostic scheme based on the polarization amplitude defined via twist operator, evaluated within the infinite density-matrix renormalization group framework. As a benchmark, an analysis of the spin-$\frac{1}{2}$ XXZ chain demonstrates that the polarization amplitude clearly distinguishes the gapless Tomonaga-Luttinger liquid from the gapped Néel phase. We then extend this framework to infinite cylinders of the spin-$\frac{1}{2}$ XY-$J_{\chi }$ model on the square lattice. We find that the polarization amplitude sharply detects the transition between the gapless XY phase and the gapped chiral spin liquid phase. These results show that polarization amplitudes provide a strong energy gap diagnostic in two-dimensional frustrated quantum magnets, including quantum spin liquids.

Rare-earth dopants in silicon offer a direct photonic interface for quantum networking, yet their deployment in dense, scalable arrays is hindered by decoherence arising from magnetic dipolar and exchange interactions between neighboring spins. Here we propose a symmetry-protected superexchange design in which local ligand symmetry is engineered to suppress the dominant decoherence channel from anisotropic exchange in the regime where the unsigned short-range exchange scale exceeds the dipolar background. Focusing on erbium-doped silicon with oxygen bridges, we decompose the exchange interaction into its irreducible representation—scalar, Dzyaloshinskii–Moriya (DM), and symmetric anisotropy—and identify a crossover regime at subnanometer separations where this unsigned short-range exchange diagnostic exceeds the dipolar background. We demonstrate that inversion-symmetric oxygen motifs strictly forbid the antisymmetric DM vector and constrain the symmetric tensor, effectively decoupling isotropic exchange from noise-generating anisotropic terms. A perturbative treatment of superexchange, benchmarked against first-principles calculations, reveals that optimized symmetric geometries retain substantially higher RB fidelity than asymmetric configurations—for example, the protected two-spin benchmark remains near 0.97–0.98 after 50 gates, whereas symmetry-broken cases fall to roughly 0.6—while the weaker magnetic dipolar background remains as a residual noise source. Furthermore, statistical modeling indicates finite projected protected-motif probabilities under implantation-scale placement disorder, providing a practical route to high-density, optically addressable quantum registers.

Magnetic phases with quantum entanglement are often expressed in terms of parton wavefunctions. Relatively few examples are known in which wavefunctions can be directly written down in the spin basis. In this article, we consider the spin-$S$ Kitaev model in one dimension. For $S=1/2$, its eigenstates can be written using a Jordan-Wigner fermionic representation. Here, we present ground-state wavefunctions for any $S$ directly in the spin basis. The states we propose are valence bond arrangements, with bonds having singlet or triplet character for $S=1/2$. For $S>1/2$, we use bond states that serve as analogs of singlets and triplets. We establish the validity of our wavefunctions using a perturbative approach starting from an anisotropic limit. For half-integer $S$ and periodic boundaries, we have exponential ground-state degeneracy. The ground states are subject to a nonlocal constraint. They have ‘‘triplets’’ superposed on a background of singlets, but with the total number of triplets constrained to be even. For integer $S$, a unique ground state emerges, composed purely of triplets. Our spin-basis wavefunctions, while not exact, capture the dominant weight of the ground state(s). We obtain good agreement with exact diagonalization wavefunctions and Jordan-Wigner spectra.

Semilocal functionals are widely recognized as insufficient for capturing electronic structure of quantum materials due to inadequate treatment of electronic correlations, necessitating beyond-semilocal approaches. However, such beyond-semilocal functionals currently lack a scheme to compute electron-phonon coupling (EPC) accurately and consistently from first-principles. This gap hinders understanding of quantum phenomena like superconductivity in FeSe, leaving its EPC-driven nature debated. Here, we bridge it by developing an atomic-orbital-based framework that delivers full functional consistency across all components of EPC properties, applicable to both semilocal functionals and beyond. Using the Heyd-Scuseria-Ernzerhof (HSE) functional, we successfully predict the superconducting properties of bulk FeSe, including its ambient-pressure behavior and pressure-dependent dome. HSE accurately captures key structural and electronic characteristics, i.e., Se height, band topology, and phonon spectra, and significantly enhances EPC matrix elements, ultimately yielding superconducting transition temperatures close to experiments. Thus, our work not only developed an algorithm to calculate EPC beyond semilocal functional, but also demonstrates the importance of advanced functionals for understanding EPC-driven properties.

Gutzwiller projections of noninteracting chiral topological phases are known to give rise to fractional, topologically ordered chiral phases. Here, we carry out a similar construction using two copies of noninteracting Euler insulators to produce a class of spinful interacting Euler models. To that end, we take advantage of the recently discovered exact representation of certain Euler insulators by a projected entangled-pair state (PEPS) of bond dimension $D=2$. The Gutzwiller projection can be implemented within the tensor-network formalism, giving rise to a new PEPS of bond dimension $D=4$. We, moreover, apply very recent state-of-the-art tensor-network tools to evaluate these phases. In particular, we analyze its entanglement entropy scaling and find no topological correction to the area law, indicating that the state is not intrinsically topologically ordered. Its entanglement spectrum shows a clear cusp at momentum zero, similar to noninteracting Euler insulators, and the spectrum of the transfer operator indicates that the state is gapped, which implies nonintrinsic topological features.

This article discusses electromagnetic properties of volumetric metamaterial samples with essentially discrete structure, that is, assembled as a periodic array of electromagnetic resonators. We develop an efficient numerical procedure for precise calculation of quasistatic electromagnetic response so that samples containing several million meta-atoms can be analyzed. We demonstrate that, contrary to common belief, even million-“atoms” samples with sharp edges are still quite different from uniform (“homogenized”) materials, and their properties are critically sensitive to their shape and boundary structure. We compare our results with calculations based on the discrete dipole approximation as well as with an integral model for continuous particles, and analyze distinctions and similarities between the different approaches. In particular, discrete metamaterials present themselves as a stringent platform for assessing continuous models developed for finite objects with sharp edges. Overall, the reported results should be important for understanding mesoscopic systems with strongly interacting elements.

The interaction-driven evolution from a Fermi liquid to a Mott insulator is a hallmark of strongly correlated fermion systems. In this work, we present a numerically unbiased study of such metal-to-insulator crossover in the half-filled square-lattice Hubbard model at finite temperatures, employing auxiliary-field quantum Monte Carlo method. By jointly analyzing thermodynamic and dynamical observables, we establish the crossover diagram of the model in the temperature-interaction ($T\text{−}U$) plane. With increasing $U$, our numerical results reveal an extended crossover regime, which we refer to as the bad metal, that separates the Fermi liquid and Mott insulator. During the crossover, we also examine the antiferromagnetic spin correlations and observe pronounced nodal-antinodal dichotomy in the momentum-resolved single-particle spectral functions. Furthermore, we investigate the temperature dependence of several commonly used observables in the model. As representative results, we achieve an accurate map of the thermal entropy across the crossover diagram, and identify the parameter regions in which the model exhibits the Pomeranchuk cooling, characterized by an adiabatic cooling with increasing $U$. Beyond offering a more refined understanding of the crossover phenomenon, our work also provides valuable benchmark and guideline for future optical lattice experiments on the square-lattice Hubbard model.

The GW plus Bethe-Salpeter equation (GW-BSE) formalism is a well-established approach for calculating excitation energies and optical spectra of molecules, nanostructures, and crystalline materials. We implement GW-BSE in the cp2k code and validate the implementation for a standard organic molecular test set, obtaining excellent agreement with reference data, with a mean absolute error in excitation energies below 3 meV. We then study optical spectra of nanographenes of increasing length, showing excellent agreement with experiment. We further compute the size of the excitation of the lowest optically active excitation, which converges to about 7.6 Å with increasing length. Comparison with time-dependent density functional theory using functionals of varying exact-exchange fraction shows that none reproduce both the size of the excitation and optical spectra of GW-BSE, underscoring the need for many-body methods for accurate description of electronic excitations in nanostructures.