The prediction and subsequent discovery of topological semimetal phases of matter in solid state systems has instigated a surge of activity investigating the exotic properties of these unusual materials. Among these are transport signatures which can be attributed to the chiral anomaly; the breaking of classical chiral symmetry in a quantum theory. This remarkable quantum phenomenon, first discovered in the context of particle physics has now found new life in condensed-matter physics, connecting topological quantum matter and band theory with effective field theoretic models. In this paper we investigate the interplay between interactions and the chiral anomaly in field theories inspired by semimetals using Fujikawa's path integral method. Starting from models in one spatial dimension we discuss how the presence of interactions can affect the consequences of the chiral anomaly leading to renormalization of excitations and their transport properties. This is then generalized to the three-dimensional case where we show that the anomalous response of the system, namely, the chiral magnetic and quantum Hall effects, are modified by the presence of interactions. These properties are investigated further through the identification of anomalous modes which exist within interacting Weyl semimetals. These massive excitations are nonperturbative in nature and are a direct consequence of the chiral anomaly. The effects of interactions on mixed axial-gravitational anomalies are then investigated and the conditions required for interaction effects to be observed are discussed.

Excitons are compound particles formed from an electron and a hole in semiconductors. The impact of this substructure on the phonon-exciton interaction is described by a closed system of microscopic scattering equations. To calculate the actual excitonic thermalization properties beyond the pure bosonic picture, this equation is derived directly from an electron-hole picture within the Heisenberg equation of motion framework. In addition to the well-known bosonic character of the compound particles, we identified processes of a repulsive, fermionic type, as well as attractive carrier exchange contributing to the scattering process. In this analytical study we give general statements about the thermalization of excitons in two- and three-dimensional semiconductors. We give insights on the strong dependence of the thermalization characteristics of the exciton Bohr radius and the thermalization wavelength. Above all, we analytically provide arguments why a bosonic behavior of excitons—such as an enhanced ground-state occupation—requires the dominant phonon scattering to be quasielastic. Acoustic phonons tend to fulfill this, as each scattering event only takes small amounts of energy out of the distribution, while optical phonons tend to prevent macroscopic occupations of the lowest exciton state, since the Pauli repulsion between the individual carriers will then dominate the thermalization dynamics.

Nonlinear responses in crystalline solids are attracting a great deal of attention because of exciting phenomena, such as the bulk photovoltaic effect in noncentrosymmetric crystals and the third-harmonic generation related to Higgs modes in superconductors, and their potential applicability to electronic devices. Recently, nonlinear responses have also been studied in strongly correlated electron systems. Experimental evidence has revealed that correlations play a significant role in nonlinear responses. However, most theoretical calculations only consider excitonic effects or involve numerically demanding approaches, making interpreting the results challenging. In this paper, we adopt another approach, which is based on real-time evolution using the correlation expansion method. We focus in particular on the one-dimensional interacting Rice-Mele model. We analyze the impact of the density-density interaction on the linear and nonlinear conductivities, and we demonstrate that two-particle correlations beyond the mean-field level enhance second-order nonlinear responses, especially the second-harmonic generation, while the linear response is not strongly affected. Furthermore, by decomposing the current into a one-particle contribution and six two-particle contributions, we show that the “biexciton transition” term and its nonlinear oscillations are the most dominant two-particle contribution to the nonlinear response. In addition, we also show that the intercell charge-charge correlation is strongly enhanced when the system is driven with the frequency corresponding to the excitonic peak, and it can even exceed the intracell correlation. This implies the possibility of manipulating two-particle correlations with external fields.

We investigate a $2+1\mathrm{D}$ interacting Dirac semimetal with on-site flavor SU(2) symmetry. Topological considerations imply that the skyrmions in the flavor-symmetry-breaking phase carry electron quantum numbers, motivating a dual bosonized low-energy description in terms of two complex scalars coupled to anAbelian Chern-Simons field. We propose that the transition between a nearby Chern insulator and the flavor-symmetry-broken phase is a bicritical point in the bosonized description, and also suggest that the Gross-Neveu-Heisenberg (GNH) transition between the Dirac semimetal and the flavor-symmetry-broken phase is a tricritical point. Heuristically, the dual description corresponds to the gap closing of fermionic skyrmions. We discuss implications and potential issues with our proposal and, motivated from it, perform extensive unbiased determinantal quantum Monte Carlo (DQMC) simulations on a lattice regularized Hamiltonian for the GNH transition, extending previously available results. We compare DQMC results with the estimates in the proposed dual to available perturbative renormalization group results. We also numerically demonstrate the presence of fermionic skyrmions in the symmetry-broken phase of our lattice model.

Nonreciprocal transport in uniform systems has attracted great research interest recently and the existing theories mainly focus on the diffusive regime. In this study, we uncover a scenario for nonreciprocal charge transport in the ballistic regime enabled by asymmetric band structures of the system. The asymmetry of the bands induces unequal Coulomb potentials within the system as the bias voltage imposed by the electrodes inverts its sign. As a result, the bands undergo different energy shifts as the current flows in opposite directions, giving rise to the nonreciprocity. Utilizing the gauge-invariant nonlinear transport theory, we show that the nonreciprocal transport predominantly originates from the second-order conductance, which violates the Onsager reciprocal relation but fulfills a generalized reciprocal relation similar to that of unidirectional magnetoresistance. The ballistic nonreciprocal transport phenomena differ from the diffusive ones by considering the internal asymmetric Coulomb potential, a factor not accounted for in diffusive cases but undeniably crucial in ballistic scenarios. Our work opens an avenue for implementing nonreciprocal transport in the ballistic regime and provides an alternative perspective for further experimental explorations for nonreciprocal transport.

Bulk transition-metal dichalcogenides (TMDs) materials are becoming attractive candidates for the study of light-matter interactions and manipulation of light emission due to its surprisingly high refractive index in visible to infrared range. Here, we propose a nanoresonator composed of bulk tungsten disulfide (${\mathrm{WS}}_2$) as an all-dielectric nanoantenna, demonstrating its capability in controlling the emission of light. We demonstrate that the ${\mathrm{WS}}_2$ nanowire can efficiently control the emission directionality of an adjacent quantum emitter via multimode interference and self-hybridization. The influence of oscillator strength of the intrinsic excitonic mode on the directional emission property is investigated. We reveal that exciton-Mie self-hybridization can effectively modulate the emission directionality leading to a dramatic suppression of directional emission at the excitonic resonances. We also demonstrate that the light emission from monolayer ${\mathrm{WS}}_2$ can be controlled by adjusting the radius of the nanowire, achieving unidirectional and directional radiation at different nanowire radius, which is attributed to the mutual interference between different optical modes. The proposed system is expected to offer a promising route for potential applications in ultracompact and multiplexed integrated photonic devices.

We propose a method to efficiently compute the entanglement entropy (EE) of quantum many-body systems. Our approach, called the incremental SWAP operator method, combines the simplicity of the SWAP operator used in projector quantum Monte Carlo simulations with recent advances in precisely computing exponential observables using incremental algorithms. We apply this technique to obtain accurate EE data at reduced computational cost for 1D and 2D antiferromagnetic Heisenberg models with different bipartition schemes. Using the computed EE data, we extract the area law coefficient, universal logarithmic corrections from Goldstone modes, and the geometric constant, finding quantitative agreement with analytical predictions. Moreover, in an unbiased numerical simulation of 2D antiferromagnetic Heisenberg model, we successfully obtain reliable universal logarithmic corrections from sharp corners that match expected theoretical values. The consistency between our numerical results and theoretical calculations demonstrates the power of our approach for accessing challenging universal entanglement properties. The extensions of our method to other quantum spin/boson models and the interacting fermion models are outlined.

Ordinary superconductors are widely assumed insensitive to small concentrations of random nonmagnetic impurities, whereas strong disorder suppresses superconductivity, ultimately leading to a superconductor-insulator transition. In between these limiting cases, a most fascinating regime may emerge where disorder enhances superconductivity. This effect is discussed here for the $\beta$ phase of vanadium-titanium alloys. Disorder is modeled using the coherent potential approximation while local electronic interactions are treated using dynamical mean-field theory. The McMillan formula is employed to estimate the superconducting transition temperature, showing a maximum at a Ti concentration of around 0.33 for a local Coulomb interaction $U$ in the range of 2 eV to 3 eV. Our calculations quantitatively agree with the experimentally observed concentration-dependent increase of $T_c$, and its maximal value of about $20\%$.

We study an optical Raman square lattice with $\mathrm{U}\left(1\right)$ synthetic gauge flux to show a chiral spin liquid (CSL) phase for cold atoms based on slave-rotor and spinon mean-field theories, respectively. An effective U(1) gauge flux generated by Raman potentials plays a major role in realizing the CSL phase. By using slave-rotor techniques we find the CSL phase at a strong on-site Fermi Hubbard interacting regime. For large value of Hubbard interaction, we derive an effective spin model including up to the four spin interactions. By spinon mean-field analysis it is shown that the CSL phase is stabilized in the case of strong magnetic frustration. Two mean-field approximation methods give consistent phase diagrams and provide qualitative numerical evidence of the CSL phase.

As one of the most intriguing states of matter, the chiral spin liquid (CSL) has attracted much scientific interest while its existence and mechanism in crystalline strongly correlated systems remain hotly debated. On the other hand, strong correlation driven emergent phenomena can be realized in twisted transition metal dichalcogenide bilayers with a tremendously tunable large length scale providing a new platform for the emergence of CSLs. We focus on a strongly correlated model relevant to heterobilayer ${\text{WSe}}_2/{\text{MoSe}}_2$ and investigate the Mott insulating phase at half filling under an out-of-plane magnetic field. Considering both its orbital and spin Zeeman effects we identify three conventionally ordered phases including a ${120}^{\circ }$ Néel phase, a stripe phase, and an up-up-down phase. For intermediate fields an emergent quantum spin liquid phase is identified with partial spin polarization. We further characterize its topological nature as the $\nu =1/2$ Laughlin CSL through the topological entanglement spectrum and quantized spin pumping under spin flux insertion. In addition, we map out the quantum phase diagram for different twisted angles in an experimentally accessible parameter regime.

The complete characterization of a generic $d$-dimensional Floquet topological phase is usually hard for the requirement of information about the micromotion throughout the entire driving period. In a recent work [L. Zhang et al., Phys. Rev. Lett. 125, 183001 (2020)], an experimentally feasible dynamical detection scheme was proposed to characterize the integer Floquet topological phases using quantum quenches. However, this theory is still far away from completion, especially for free-fermion Floquet topological phases, where the states can also be characterized by ${\mathcal{Z}}_2$ invariants. Here we develop a full and unified dynamical characterization theory for the ${\mathcal{Z}}_2$ Floquet topological phases of different dimensionality and tenfold-way symmetry classes by quenching the system from a trivial and static initial state to the Floquet topological regime through suddenly changing the parameters and turning on the periodic driving. By measuring the minimal information of Floquet bands via the stroboscopic time-averaged spin polarizations, we show that the topological spin texture patterns emerging on certain discrete momenta of Brillouin zone called the 0 or $\pi$ gap highest-order band-inversion surfaces provide a measurable dynamical ${\mathcal{Z}}_2$ Floquet invariant, which uniquely determines the Floquet boundary modes in the corresponding quasienergy gap and characterizes the ${\mathcal{Z}}_2$ Floquet topology. The applications of our theory are illustrated via one- and two-dimensional models that are accessible in current quantum simulation experiments. Our work provides a highly feasible way to detect the ${\mathcal{Z}}_2$ Floquet topology and completes the dynamical characterization for the full tenfold classes of Floquet topological phases, which shall advance the research in theory and experiments.

The Emery model, or three-band Hubbard model, is a Hamiltonian that is thought to contain much of the physics of cuprate superconductors. This model includes two noninteracting $p$ orbitals and one interacting $d$ orbital per unit cell. Few methods that can solve multiorbital interacting Hamiltonians reliably and efficiently exist. Here, we introduce an application of the two-particle self-consistent (TPSC) approach to the Emery model. We construct this method within the framework of the TPSC $+$ DMFT method, which can be seen as a way to introduce nonlocal corrections to dynamical mean-field theory (DMFT). We show that interacting orbital densities, rather than the noninteracting ones, must be used in the calculations. For the Emery model, we find that at constant bare interaction $U$, the vertex for spin fluctuations, $U_{sp}$, decreases rapidly with filling. This may be one of the factors that contributes to electron-doped cuprates appearing less correlated than hole-doped ones. More generally, our work opens the road to the application of the TPSC approach to spin fluctuations in multiorbital models.

Due to the recent studies of the fracton topological phases, the host of which deconfined quasiparticle excitations with mobility restrictions, the concept of symmetries has been updated. Focusing on one of these new symmetries, multipole symmetries, including global, dipole, and quadruple symmetries, and gauge fields associated with them, we construct new sets of ${\mathbb{Z}}_N(2+1)$-dimensional foliated background-field (BF) theories, where BF theories of conventional topological phases are stacked in layers with couplings between them. By investigating gauge-invariant nonlocal operators, we show that our foliated BF theories exhibit unusual ground-state degeneracy depending on the system size; it depends on the greatest common divisor between $N$ and the system size. Our result provides an important connection between UV lattice models of the fracton topological phases and other unconventional ones in view of foliated field theories.

An emergent and promising tensor-network-based impurity solver is to represent the Feynman-Vernon influence functional as a matrix product state, where the bath is integrated out analytically. Here we present an approach to calculate the equilibrium impurity spectral function based on the recently proposed Grassmann time-evolving matrix product operators method. The central idea is to perform a quench from a separable impurity-bath initial state as in the nonequilibrium scenario. The retarded Green's function $G(t+t_0,t^{\prime }+t_0)$ is then calculated after an equilibration time $t_0$ such that the impurity and bath are approximately in thermal equilibrium. There are two major advantages of this method. First, since we focus on real-time dynamics, we do not need to perform the numerically ill-posed analytic continuation as in imaginary- time evolution-based methods. Second, the required bond dimension of the matrix product state in real-time calculations is observed to be much smaller than that in imaginary-time calculations, leading to a significant improvement in numerical efficiency. The accuracy of this method is demonstrated using the single-orbital Anderson impurity model and benchmarked against the continuous-time quantum Monte Carlo method.

Strong local disorder in interacting quantum spin chains can turn delocalized eigenmodes into localized eigenstates, giving rise to many-body localized phases. This is accompanied by distinct spectral statistics: chaotic for the delocalized phase and integrable for the localized phase. In isolated systems, localization and chaos are defined through a web of relations among eigenvalues, eigenvectors, and real-time dynamics. These may change as the system is made open. We ask whether random dissipation (without random disorder) can induce chaotic or localized behavior in an otherwise integrable system. The dissipation is described using non-Hermitian Hamiltonians, which can effectively be obtained from Markovian dynamics conditioned on null measurement. In this non-Hermitian setting, we argue in favor of the use of the singular value decomposition. We complement the singular value statistics with different diagnostic tools, namely, the singular form factor and the inverse participation ratio and entanglement entropy of singular vectors. We thus identify a crossover of the singular values from chaotic to integrable spectral features and of the singular vectors from delocalization to localization. Our method is illustrated in an XXZ Hamiltonian with random local dissipation.

Moiré superlattices have become an emergent solid-state platform for simulating quantum lattice models. However, in a single moiré device, Hamiltonian parameters like the lattice constant, hopping, and interaction terms can hardly be manipulated, limiting the controllability and accessibility of a moiré quantum simulator. Here, by combining angle-resolved photoemission spectroscopy and theoretical analysis, we demonstrate that high-order moiré patterns in graphene-monolayered xenon/krypton heterostructures can simulate a honeycomb model in the mesoscale, with in situ tunable Hamiltonian parameters. The length scale of the simulated lattice constant can be tuned by annealing processes, which in situ adjusts intervalley interaction and hopping parameters in the simulated honeycomb lattice. The sign of the lattice constant can be switched by choosing a xenon or krypton monolayer deposited on graphene, which controls the sublattice degree of freedom and valley arrangement of Dirac fermions. In this letter, we establish a path for experimentally simulating the honeycomb model with tunable parameters by high-order moiré patterns.

Experimental measurements for the conversion loss between electric and mechanical energies of (Mg,Zn)O-based resonators show that Mg substitution can improve the electromechanical coupling of the wurtzite ZnO films up to the substitution concentration of 35%. Extended x-ray absorption fine structure (EXAFS) experiments indicate that both Mg and Zn exhibit tetrahedral local structures in (Mg,Zn)O films. With an increase in the Mg substitution concentration, the Zn-O bond length shows a slight tendency to increase and the Mg-O bond length practically remains the same. Further analysis of the EXAFS spectra reveals that a ${\mathrm{MgO}}_4$ tetrahedron cluster exists in the oxide alloy. First-principles calculations reproduce the experimental results, suggesting that the enhanced electromechanical coupling is mainly attributed to a decrease in the dielectric constant due to the Mg substitution. The enhancement in piezoelectricity caused by Mg substitution originates from an increase in the Zn-O bond length along the $c$ axis, which enhances the $c$-axis-oriented electric dipole moment. Furthermore, the calculations show that the Mg substitution can reduce the critical transition pressure from the wurtzite phase to the rocksalt phase. This study shows that combining the EXAFS experiment and theoretical calculation is a reliable method for understanding the relationship between the electromechanical coupling and local cation structure in wurtzite alloy systems. This can guide the search for novel piezoelectric materials.

Recently, there is an interest in studying the bulk-edge correspondence for nonlinear eigenvalue problems in a two-dimensional topological system with spin-orbit coupling. By employing the method of the auxiliary eigenvalues as introduced in T. Isobe et al., Phys. Rev. Lett. 132, 126601 (2024), the nonlinear bulk-edge correspondence was established. In this paper, taking the Haldane model as an example, we address that such a correspondence will appear in two-dimensional topological systems without spin-orbit coupling. The resulting edge states are characterized by the Chern number of the auxiliary energy band. A full phase diagram containing topological nontrivial phase, topological trivial phase, and metallic phase is obtained. Our work generalizes the study of the bulk-edge correspondence for nonlinear eigenvalue problems in two-dimensional systems.

The short time evolution of a topological system after a sudden quench is considered, calculating the Loschmidt rate and studying in detail the distribution of Fisher zeros. Singular behavior in the Loschmidt rate has been predicted and found in several systems and, in particular, in one dimension (1D) one finds sharp features in the time evolution of the Loschmidt rate. These are associated with critical times that may be seen as the imaginary part of the Fisher zeros, under the condition that their real part vanishes. In the complex plane one finds lines of zeros that cross the imaginary axis at certain points. In a 2D system, in general, the Fisher zeros occupy areas instead of lines, as shown before, with the consequences that a continuous set of critical times results along the imaginary axis and that one does not find a well defined singular behavior in the Loschmidt rate. Here we show that several 2D topological systems also display very narrow regions (effectively lines) of zeros, in addition to finite extent areas of zeros. As a consequence, well defined sharp critical times are found, under appropriate conditions. An example is a $2\text{D}p$-wave superconductor in the presence of a magnetic field, but other systems share the same property, such as a Haldane insulator, a system with an anomalous Hall effect, and topological insulators. Details on the momentum distribution of the real and imaginary parts of the Fisher zeros are discussed, clarifying the existence of the lines of zeros and taking as an example the $p$-wave superconductor in magnetic field. The time dependence of the Loschmidt rate phase and of the Pancharatnam geometrical phase is considered, for different times after the quench and as a function of momentum. Pairs of vortices and antivortices in the phase associated with the geometric phase and the Loschmidt rate phase, that have been proposed for some 2D systems, are also shown to appear in the regime where we find lines of zeros.

A detailed study of the magnetic and magnetocaloric properties of the garnet compound ${\mathrm{Mn}}_3{\mathrm{Cr}}_2{\mathrm{Ge}}_3{\mathrm{O}}_{12}$ is carried out using x-ray diffraction, magnetization, heat capacity, and neutron diffraction measurements as well as ab initio band-structure calculations. This compound manifests two successive magnetic transitions at $T_{\mathrm{N}1}\simeq 4.5\mathrm{K}$ and $T_{\mathrm{N}2}\simeq 2.7\mathrm{K}$. Neutron powder diffraction experiments reveal that these two transitions correspond to the collinear and noncollinear antiferromagnetic ordering of the nonfrustrated ${\mathrm{Cr}}^{3+}$ and frustrated ${\mathrm{Mn}}^{2+}$ sublattices, respectively. The interactions within each of the Cr and Mn sublattices are antiferromagnetic, while the intersublattice interactions are ferromagnetic. The H-T phase diagram is quite complex and displays multiple phases under magnetic field, which can be attributed to the frustrated nature of the spin lattice. ${\mathrm{Mn}}_3{\mathrm{Cr}}_2{\mathrm{Ge}}_3{\mathrm{O}}_{12}$ shows a large magnetocaloric effect with a maximum value of isothermal entropy change $\mathrm{\Delta }{S}_{\mathrm{m}}\simeq -23$ J/kg K and adiabatic temperature change $\mathrm{\Delta }{T}_{\mathrm{ad}}\simeq 9\mathrm{K}$ for a field change of 7 T. Further, a large value of the relative cooling power ($RCP\simeq 360$ J/kg) demonstrates the promise of using this compound in magnetic refrigeration.