The physics of strongly correlated fermions described by Hubbard or $t\text{−}J$ models in the underdoped regime—relevant for high-temperature superconductivity in cuprate compounds—remains a subject of ongoing debate. In particular, the nature of charge carriers in this regime is poorly understood, in part due to the unusual properties of their spectral function. In this Letter, we present unbiased numerical results for the one-hole spectral function in a $t\text{−}J$ model at finite temperatures. Our study provides valuable insights into the underlying physics of magnetic (or spin-) polaron formation in a doped antiferromagnet (AFM). For example, we find how the suppression of spectral weight outside the magnetic Brillouin zone—a precursor of Fermi arc formation–disappears with increasing temperature, revealing nearly-deconfined spinon excitations of the undoped AFM. The pristine setting we consider can be directly explored using quantum simulators. Our calculations demonstrate that coherent quasiparticle peaks associated with magnetic polarons can be observed up to temperatures $T>J$ above the spin-exchange $J$, routinely obtained in such experiments. This paves the way for future studies of the fate of magnetic polarons in the pseudogap phase.

Due to significant progress in quantum gas microscopy in recent years, there is a rapidly growing interest in real-space properties of single mobile dopands created in correlated antiferromagnetic (AFM) Mott insulators. However, a detailed numerical description remains challenging, even for simple toy models. As a consequence, previous numerical simulations for large systems were largely limited to $T=0$. To provide guidance for cold-atom experiments, numerical calculations at finite temperature are required. Here, we numerically study the real-time properties of a single mobile hole in the 2D $t\text{−}J$ model at finite temperature and draw a comparison to features observed at $T=0$. We find that a three-stage process of hole motion, which was reported at $T=0$, is valid even at finite temperature. However, already at low temperatures, the average hole velocity at long times is not simply proportional to the spin coupling, contrary to the $T=0$ behavior. Comparing our finite-temperature numerical results with the experimental data from quantum gas microscopy we find a qualitative disagreement: in experiment, hole spreading speeds up with increasing $J/t$, while in our numerics it slows down. The latter is consistent with the numerical findings previously reported at $T=0$.

We develop an analytical and self-consistent thermodynamic model for carbyne using the unsymmetrized self-consistent field theory. By deriving closed-form expressions for the Helmholtz and Gibbs free energies, as well as vibrational and response functions, we analyze the temperature dependence of self-consistent potentials and one-particle distributions. Our results demonstrate that quantum and classical anharmonicities reshape the effective potential landscape, driving spontaneous symmetry breaking and a thermodynamic phase transition from cumulene to polyyne. The resulting analytical phase diagram reveals how thermal effects govern the structural stability of one-dimensional carbon chains.

We introduce a versatile and scalable framework for constructing effective models of superconducting (SC) nanostructures described by the generalized SC Anderson impurity model with multiple quantum dots and leads. Our chain expansion (ChE) method maps each SC lead onto a finite tight-binding chain with parameters obtained from Padé approximants of the tunneling self-energy. We provide an explicit algorithm for the general case as well as simple analytical expressions for the chain parameters in the wide-band and infinite-chain limits. This mapping preserves low-energy physics while enabling efficient simulations: short chains are tractable using exact diagonalization, and longer ones are handled with density matrix renormalization group methods. The approach remains reliable and computationally efficient across diverse geometries, both in and out of equilibrium. We use ChE to map the ground-state phase diagrams of double, triple, and quadruple quantum dots coupled to a single SC lead. While half-filled symmetric systems show similar overall diagrams, the particular phases differ substantially with the dot number. Here, large parameter regions are entirely missed by the widely used zero-bandwidth approximation but are captured by ChE. Away from half-filling, additional dots markedly increase diagram complexity, producing a rich variety of stable phases. These results demonstrate ChE as a fast, accurate, and systematically improvable tool for exploring complex SC nanostructures.

Weyl quasiparticles, as gapless low-energy excitations with nontrivial chirality, have garnered extensive interest in recent years. However, archieving effective and reversible control over their chirality (topological charge) remains a major challenge due to topological protection. In this Letter, we propose a ferroelectric mechanism to switch the chirality of Weyl phonons, where the reversal of ferroelectric polarization is intrinsically coupled to a simultaneous reversal of the chirality of Weyl points. This enables electric-field-driven control over the topological properties of phonon excitations. Through a comprehensive symmetry analysis of polar space groups, we identify 27 groups capable of hosting symmetry-protected Weyl phonons with chiral charges $C=1$, 2, and 3, whose chirality can be reversed via polarization switching. The first-principles calculations are performed to screen feasible material candidates for each type of chirality, yielding a set of prototypical ferroelectric compounds that realize the proposed mechanism. As a representative example, ${\mathrm{K}}_2{\mathrm{ZnBr}}_4$ hosts the minimal configuration of two pairs of Weyl phonons. Upon polarization reversal, the chirality of all Weyl points is inverted, accompanied by a reversal of associated topological features such as Berry curvature and surface arcs. These findings provide a viable pathway for dynamic, electrical control of topological band crossings and open different avenues for chirality-based phononic applications.

Noncollinear antiferromagnets (nAFMs) with a small net magnetic moment offer new opportunities for ultrafast spintronic devices, owing to unique physical properties. While in ferromagnets and collinear AFMs the spin current polarization is locked to the magnetization $\widehat{\mathbf{m}}$ and Néel vector $\widehat{\mathbf{n}}$ directions, we predict that magnon spin currents injected by metal contacts into nAFMs can be polarized with both $\widehat{\mathbf{n}}$ and $\widehat{\mathbf{m}}$ components when carried by a coherent superposition of magnon eigenstates. The spin injection efficiency is governed by an interface spin conductance tensor that depends on the noncollinear magnetic texture. While the $\widehat{\mathbf{m}}$ component diffuses freely into the nAFM, the $\widehat{\mathbf{n}}$ component oscillates as a function of distance from the injector and applied magnetic field, analogous to the Hanle effect of electron spins in metals. Our findings reveal the potential of nAFMs as platforms for the study of tensorial coherent spin transport.

Quantum anomalous Hall (QAH) insulators exhibit chiral dissipationless edge states without an external magnetic field, making them a promising material for quantum metrology and microwave applications. However, the breakdown of the zero-resistance state at low currents hinders progress. We investigate and characterize this breakdown under microwave fields (1–25 GHz) by measuring the increase of longitudinal resistance in RF Hall bars and RF Corbino devices made from V-doped ${\left(\mathrm{Bi},\mathrm{Sb}\right)}_2{\mathrm{Te}}_3$ films. Our results point to the role of heating of electron-hole puddles under microwave irradiation, thereby fostering hopping transport. Our work offers insights critical for GHz-range QAH applications.

Spin pumping is a microwave-driven means for injecting spins from a ferromagnet into the adjacent target material. The insertion of a thin antiferromagnetic layer between the ferromagnet and the target material is known to enhance the spin pumping signal. Here, in view of describing dynamic fluctuations of the Néel order parameter, we develop Ginzburg-Landau theory of the spin pumping in a ferromagnet/antiferromagnet/heavy metal trilayer in the vicinity of the antiferromagnetic Néel temperature $T_{\mathrm{N}}$. When there exists an interfacial exchange interaction between the ferromagnetic spins and the antiferromagnetic Néel order parameter at the ferromagnet/antiferromagnet interface, we find a strongly frequency-dependent enhancement of the pumped spin current that is peaked at $T_{\mathrm{N}}$. The present finding offers an explanation for the enhanced spin pumping with strong frequency dependence observed in a ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}/\mathrm{CoO}/\mathrm{Pt}$ system.

The Comment [Y.-M. Li, B. Wei, and K. Chang, Phys. Rev. Lett. 132, 219601 (2024)] pointed out that it is incorrect to predict the temperature-driven topological phase transition of Dirac magnons in honeycomb ferromagnets with Dzyaloshinskii-Moriya interactions based on the theory in Lu et al. [Y.-S. Lu, J.-L. Li, and C.-T. Wu, Phys. Rev. Lett. 127, 217202 (2021)]. Here we propose that by breaking the sublattice symmetries in honeycomb ferromagnets, increasing temperature could induce topological transitions from the trivial phase at zero temperature based on the linear spin wave theory to the Chern insulating phase above a critical temperature without changing any spin-spin interactions. The key to the finite-temperature topological magnons is considering the magnon-magnon interactions (MMIs) at a mean-field level. A self-consistently renormalized spin wave theory is employed to include self-energy corrections from MMIs, guaranteeing that the critical temperatures for topological transitions are below the Curié temperatures. Across the critical temperatures, the magnon band gap closes and reopens at $\mathbf{K}$ or ${\mathbf{K}}^{\prime }$ points in the Brillouin zone, accompanied by nontrivial Berry curvature transitions. However, in stark contrast to the work of Lu et al. [Phys. Rev. Lett. 127, 217202 (2021)], the topological transitions cannot be revealed by the thermal Hall effect of magnons. Our work provides a realistic scheme for achieving a finite-temperature topological phase in honeycomb ferromagnets.

We show how the effects of large numbers of measurements on many-body quantum ground and thermal states can be studied using quantum Monte Carlo (QMC). Density matrices generated by measurement in this setting feature products of many local nonunitary operators, and by expanding these density matrices as sums over operator strings we arrive at a generalized stochastic series expansion (SSE). Our “post-measurement SSE” is based on importance sampling of operator strings contributing to a measured thermal density matrix. We demonstrate our algorithm by probing the effects of measurements on the spin-$1/2$ Heisenberg antiferromagnet on the square lattice. Thermal states of this system have $\mathrm{SU}\left(2\right)$ symmetry, and at first we preserve this symmetry by measuring $\mathrm{SU}\left(2\right)$ symmetric observables. We identify classes of post-measurement states for which correlations can be calculated efficiently, as well as states for which $\mathrm{SU}\left(2\right)$ symmetric measurements generate a QMC sign problem when working in any site-local basis. For the first class, we show how deterministic loop updates can be leveraged. Using our algorithm we demonstrate the creation of long-range Bell pairs and symmetry-protected topological order, as well as the measurement-induced enhancement of antiferromagnetic correlations. We then study the effects of measuring the system in a basis where the standard (unmeasured) SSE is sign-free: For measurement schemes with this property, we can calculate correlations in all post-measurement states without a sign problem. The method developed in this work opens the door to scalable experimental probes of measurement-induced collective phenomena, which require numerical estimates for the effects of measurements.

Matrix product states (MPSs) and matrix product operators (MPOs) are fundamental tools in the study of quantum many-body systems, particularly in the context of tensor network methods such as time-evolving block decimation (TEBD). However, constructing compact MPO representations for Hamiltonians with interactions beyond nearest neighbors, such as those arising in atomic, molecular, and optical (AMO) systems or in systems with ring geometry, remains a challenge. In this paper, we propose an approach for the direct construction of compact MPOs tailored specifically for the exponential of spin Hamiltonians. This approach allows for a more efficient time evolution, using TEBD, of spin systems with interactions beyond nearest neighbors, such as long-range spin chains, periodic systems, and more complex cluster models, with interactions involving more than two spins.

The discovery of metal borides with higher transition temperature ($T_{\mathrm{c}}$) has been receiving continuous attention since the observation of superconductivity in ${\mathrm{MgB}}_2$ at 39 K. Here we propose a rational design strategy for high-$T_{\mathrm{c}}$ ternary metal borides through the cosubstitution of Mg with two compensating metal elements that possess an effective isovalency of 2. Guided by this principle, we theoretically predict a collection of ternary boride superconductors, including a representative example of ${\mathrm{KAlB}}_4$ that has an isostructure to ${\mathrm{MgB}}_2$, with $T_{\mathrm{c}}$ up to 67 K at ambient pressure. Our detailed analysis reveals that, compared with ${\mathrm{MgB}}_2$, due to the Stark effect caused by the difference in valence of two metal ions, the $\sigma$ bands of B layers get significant splitting and exhibit more flat character, resulting in enhanced electronic occupation; furthermore, the softened in-plane $E_{2\mathrm{g}}$ modes produce larger deformation potential and electron-phonon coupling with B $\sigma$ states, which in turn results in larger superconducting gaps and much higher $T_{\mathrm{c}}$ value in ${\mathrm{KAlB}}_4$. We further propose a feasible synthesis route of ${\mathrm{KAlB}}_4$ to stimulate experimental progress. Our approach paves the way for finding more high-$T_{\mathrm{c}}$ ternary boride superconductors at ambient pressure.

The electronic and optical properties of the fluorides ${\mathrm{BaF}}_2$ and ${\mathrm{SrF}}_2$ with heavy metal ions ${\mathrm{Ba}}^{++}$ and ${\mathrm{Sr}}^{++}$, respectively, are studied using advanced theoretical methods across a wide energy range. The single-quasi-particle effects are described within a self-consistent treatment of the exchange-correlation self-energy in the $\mathit{GW}$ approximation. Building on an improved starting point $G_0{W}_0$, where eigenfunctions and eigenvalues are obtained from a generalized Kohn-Sham scheme with the hybrid HSE06 functional, we iterate the eigenvalues in the Green's function $G_n$ and/or the screened Coulomb potential $W_n$ until convergence. Gaps are further opened in the self-consistent procedure. Spin-orbit interaction is taken into account. It particularly influences all interband transitions from the Ba $5p$ or Sr $4p$ valence bands into the lowest conduction bands in the photon energy region $15–24\mathrm{eV}$. Excitonic effects are included in the calculation of optical spectra by solving the Bethe-Salpeter equation within the $\mathit{GW}$ framework. Moreover, to improve the results, we go beyond the Tamm-Dancoff approximation for the excitonic effects. The comparison with experimental spectra of the real and imaginary parts of the dielectric function shows that the combination of self-consistently treated quasiparticle effects, inclusion of spin-orbit coupling, and electron-hole interaction leads to excellent agreement with the measured spectra. Corrections beyond Tamm-Dancoff improve the spectra in the high-energy region.

Hyperbolic materials, featured by the hyperbolic dispersion relations of waves, enable highly directional electromagnetic modes and extreme light confinement beyond the diffraction limit. However, current realizations of hyperbolic materials rely on complex, lossy metamaterials or narrow-band phononic crystals. In this study, we propose copper oxides ${\mathrm{Ba}}_2{\mathrm{CuO}}_x$ as natural hyperbolic materials whose hyperbolic response can be tuned by altering the oxygen stoichiometry. First-principles calculations reveal that ${\mathrm{Ba}}_2{\mathrm{CuO}}_3$, which features one-dimensional (1D) Cu-O chains, behaves as an ideal quasi-1D electron gas and exhibits a broadband, low-loss type-I hyperbolic window (0.13–2.57 eV) with an exceptional quality factor ($Q$ > 50). By contrast, its fully oxidized counterpart ${\mathrm{Ba}}_2{\mathrm{CuO}}_4$, which consists of two-dimensional ${\mathrm{CuO}}_2$ planes, displays broadband type-II hyperbolicity in the range of 0.51–3.43 eV and Lorentz-driven ultraviolet type-I hyperbolicity from 4.46–5.22 eV. We also investigate the directional surface plasmon polaritons arising from the different types of equifrequency contours. These findings offer a promising platform for reconfigurable, low-loss hyperbolic photonics without the need of nanofabrication.

Systems exhibiting the Hilbert-space fragmentation are nonergodic, and their Hamiltonians decompose into exponentially many blocks in the computational basis. In many cases, these blocks can be labeled by eigenvalues of statistically localized integrals of motion (SLIOMs), which play a similar role in fragmented systems as local integrals of motion in integrable systems. While a nonzero perturbation eliminates all nontrivial conserved quantities from integrable models, we demonstrate for the $t\text{−}{J}_z$ chain that an appropriately chosen perturbation may gradually eliminate SLIOMs (one by one) by progressively merging the fragmented subspaces. This gradual recovery of ergodicity manifests as an extended critical regime characterized by multiple peaks of the fidelity susceptibility. Each peak signals a change in the number of SLIOMs and blocks, as well as an ultra-slow relaxation of local observables.

We investigate the relationship between the analytical properties of the Green's function and ${\mathbb{Z}}_2$ topological insulators, focusing on three-dimensional inversion-symmetric systems. We show that the diagonal zeros of the Green's function in the orbital basis provide a direct and visual way to calculate the strong and weak ${\mathbb{Z}}_2$ topological invariants. We introduce the surface of crossings of diagonal zeros in the Brillouin zone, and show that it separates time-reversal invariant momenta (TRIMs) of opposite parity in two-band models, enabling the visual computation of the ${\mathbb{Z}}_2$ invariants by counting the relevant TRIMs on either side. In three-band systems, a similar property holds in every case except when a trivial band is added in the band gap of a nontrivial two-band system, reminiscent of the band topology of fragile topological insulators.

The quasi-two-dimensional material ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ is a paradigmatic example of a correlated system that exhibits unconventional superconductivity and intriguing magnetic properties. The interplay between these two effects and the resulting strength and nature of spin fluctuations and their role for the properties of the compound have sparked significant debates. Here, elaborating a theory that self-consistently incorporates spatial magnetic fluctuations into a realistic many-body description, we show that these fluctuations significantly reduce many-body correlations in the system, thereby preventing magnetic ordering in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, in agreement with experimental observations. Our conclusion is supported by a theoretical calculation of the spin susceptibility that closely matches the experimental results. We obtain finite peaks at the incommensurate wave vectors, a broad dome-shaped structure centered around the $\mathrm{\Gamma }$ point, and a diminished magnetic response at the edges of the BZ. We identify the orbital character of the unusual dome structure as resulting predominantly from the 2D-like $xy$ orbital, which is believed to be responsible for the superconductivity.

In this work we analyze infinite graphene nanoribbons subjected to nonuniform magnetic fields that produce topological domain walls in the quantum Hall regime. We show how the proximity between edge states from neighboring domains modifies the band structure due to the state coupling near the domain walls. The proximity-induced band deformations produce phenomena such as bulklike dispersion that coexist with Landau levels and valley-polarized current paths. It is shown that edge state coupling can be enhanced by continuously varying the magnetic field between two nontrivial topological phases. The mechanism by which neighboring edge states modify the band structure is addressed by tracking their wave functions over isolated bands and by analyzing the magnetic confinement potential near the domain wall. By calculating the local current density, we show that the coexistence of topological edge states with bulklike dispersion can lead to the appearance of antichirality, in which copropagating currents appear in the edges while the rest of the nanoribbon is occupied with bulk states. The appearance of antichirality is justified by comparing the proposed nonuniform magnetic field profile with an antichiral modified Haldane model. The relation between the proximity effects and quantum transport is explored by conductance calculations in a multiterminal setup using the Landauer-Büttiker formalism.

We theoretically study scanning-gate microscopy (SGM) of a superconductor-proximitized semiconducting wire focusing on the potential for detection of Majorana bound states (MBSs). We exploit the possibility of creating a local potential perturbation by the scanning-gate tip which allows controllable modification of the spatial distribution of the Majorana modes, which is translated into changes in their energy structure. When the tip scans across the system, it effectively divides the wire into two parts with controllable lengths, in which two pairs of Majorana states are created when the system is in the topological regime. For strong values of the tip potential, the pairs are decoupled, and the presence of Majorana states can be detected via local tunneling spectroscopy that resolves the energy splittings resulting from the Majorana states wave functions overlap. Importantly, as the system is probed spatially via the tip, this technique can distinguish MBSs from quasi-Majorana states localized on smooth potential barriers. We demonstrate that, for weaker tip potentials, the two neighboring Majorana states hybridize, opening pronounced anticrossings in the energy spectra which are reflected in local conductance maps and which result in nonzero nonlocal conductance features. Finally, we demonstrate that the SGM technique can be used to discriminate between the trivial and topological nature of the zero-bias conductance peak in disordered wires.