We implement the recently developed influence functional matrix product states approach as impurity solver in equilibrium and nonequilibrium dynamical mean field theory (DMFT) calculations of the single-band Hubbard model. The method yields numerically exact descriptions of metallic states without sharp spectral features, at a moderate numerical cost. Systems with narrow quasiparticle or spin-polaron peaks, as well as low-temperature Mott insulators, provide more challenges since these simulations require long time contours or high bond dimensions. A promising field of application is the DMFT simulation of nonequilibrium steady states, which we demonstrate with results for photo-doped Mott systems with long-lived doublon and holon populations.

In this work, we perform a combination of analytical and numerical studies on the phase diagram of the spin-1/2 Kitaev-Heisenberg chain in the region of negative Kitaev and positive Heisenberg couplings. Apart from the antiferromagnetic phase, we find a magnetically ordered phase with left-left-right-right order and a gapless phase with central charge value $c=1$, resolving the existing contradictory results in literature regarding this parameter region. In particular, the origin of the left-left-right-right order is clarified based on a perturbative Luttinger liquid analysis. The left-left-right-right phase is further shown to persist in the Kitaev-Heisenberg-Gamma model when a small nonzero Gamma interaction is introduced. Using a coupled-chain method, we also demonstrate that the one-dimensional (1D) left-left-right-right order gives a quasi-1D explanation for the 2D stripy order of the same model on the honeycomb lattice.

In this work, we investigate the one-dimensional $XX$ lattice model and its cousins through the lens of momentum and winding $U\left(1\right)$ symmetries. We distinguish two closely related ${\mathbb{Z}}_2$ symmetries based on their relation to the $U\left(1\right)$ symmetries, and establish a web of ${\mathbb{Z}}_2$-gauging relations among these models, rooted in two fundamental seeds: the $XY\pm YX$ models. These two seeds, each self-dual under gauging of the respective ${\mathbb{Z}}_2$ symmetries, possess manifestly symmetric conserved charges, making transparent the connection between the noninvertible symmetries and the Kramers-Wannier duality. By leveraging the self-dualities of these two seed models, we derive the self-dualities of their cousins, including the $XX$ model and the Levin-Gu model, through appropriate gauging procedures. Moreover, under these gauging schemes, the lattice T-duality matrices take the form of the identity matrix. These lattice models flow to the $c=1$ compact boson conformal field theory, with a twist that depends on the lattice size modulo four. Finally, we unify the mapping structures of local conserved charges across these models, providing a comprehensive framework for understanding their symmetries and dualities.

The planar Hall effect (PHE), previously observed in Weyl and Dirac semimetals due to the chiral anomaly, emerges with a different origin in topological insulators (TIs), where in-plane magnetic fields induce resistivity anisotropy. In strictly two-dimensional TIs, PHE is generally suppressed due to the inability of the out-of-plane Berry curvature to couple to the in-plane band velocity of the charge carriers. Here, we demonstrate that in ultrathin TI films, a quasi-two-dimensional system, intersurface tunneling coupling with in-plane magnetization, induces electronic anisotropy, enabling a finite PHE. In addition, we reveal that strong in-plane magnetization can stabilize the thickness-dependent quantum anomalous Hall effect, typically associated with out-of-plane magnetization. These insights advance the understanding of magnetic topological phases, paving the way for next-generation spintronic devices and magnetic sensing technologies.

We propose an electronic refrigerator based on a ballistic Andreev interferometer that can reach a maximum cooling power per channel up to five orders of magnitude larger than that of the conventional normal metal–insulator–superconductor cooler. This effect is achieved by exploiting the destructive interference that occurs when the superconducting phase difference equals $\pi$. This results in a strongly suppressed charge current below the superconducting gap, while still allowing the extraction of excitations above the gap, leading to a cooler with enhanced performance. Interestingly, we find that such a large cooling power per channel enables the achievement of an electronic temperature close to the theoretical lower bound. Additionally, we derive an approximate expression for this bound in the regime of low bath temperatures. Finally, we propose potential implementations of the ballistic Andreev interferometer cooler using semiconductors, graphene, and topological insulators.

${\mathrm{TaRhTe}}_4$ is a type-II Weyl semimetal (WSM), exhibiting four Weyl points in proximity to the Fermi level. In this article, we report our results of a systematic study of longitudinal magnetoresistance (MR) in ${\mathrm{TaRhTe}}_4$. Our findings indicate that MR becomes negative only when the magnetic field is applied parallel to the electric field. By rotating $\mathbf{E}$ (as well as $\mathbf{B}$), we show that its origin is consistent with the prediction of the chiral anomaly, while the current jetting effect and weak localization could be excluded. The negative MR persists up to room temperature, suggesting that ${\mathrm{TaRhTe}}_4$ exhibits distinctive properties within the family of WSMs.

Recently, it was proposed that a nontrivial $Z_8$ topological index could induce double topological insulator (TI) surface states on the (001) surface of ${\mathrm{LaBaFe}}_4{\mathrm{As}}_4$ (LBFA). Here, we carry out a comprehensive investigation of the electronic structure, topological index, and topological surface states of other 1144-type iron-based compounds. We find that the coexistence of double band inversions in ${\mathrm{LaSrFe}}_4{\mathrm{As}}_4$ leads to a nontrivial $Z_8$ topological index and two sets of TI surface states on the (001) surface, similar to LBFA. On the other hand, when Ba is substituted by Ca, K, Rb, or Cs, the system is characterized by a nontrivial $Z_2$ topological index and exhibits only one set of TI surface states on the (001) surface. Further analysis shows that both the lattice parameter $c$ and the nominal valence of the alkali or alkaline earth metal atom are crucial in determining the bandwidth of La $5d_{x^2-y^2}$, topological index, and topological surface states. Moreover, we substitute La with Lu and Hf in LBFA and find that they also have a nontrivial $Z_8$ topological index. However, only one set of the double TI surface states is clearly visible on the (001) surface, whereas the other set is difficult to identify due to a different mechanism of the band inversion between As $4p_z$ and Fe $3d_{z^2}$ bands. Our findings extend previous studies on ${\mathrm{LaBaFe}}_4{\mathrm{As}}_4$ and provide insights for manipulating the topological index $Z_8$ or $Z_2$ and topological surface states in iron-based compounds.

We investigate the magnetic ground state and phase transitions in the frustrated three-dimensional system ${\mathrm{CaMn}}_2{\mathrm{P}}_2$ using first-principles calculations combined with spin-dynamics simulations. Our density functional theory (DFT) calculations, incorporating Hubbard $U$ corrections, reveal that ${\mathrm{CaMn}}_2{\mathrm{P}}_2$ exhibits an indirect gap semiconducting ground state with a localized ${\mathrm{Mn}}^{2+}$ ($3d^5$, $S=\frac{5}{2}$) electronic configuration and negligible spin-orbit coupling effects. The computed exchange interactions show that the magnetic behavior is well described by an isotropic Heisenberg Hamiltonian. In this model, there are two major couplings: The nearest-neighbor (NN) interaction $J_1$ couples the two Mn layers along the $c$ axis, and next-NN interaction $J_2$ is in the $a\text{−}b$ plane, where Mn ions form a hexagonal layer structure. Our results show that both $J_1$ and $J_2$ are antiferromagnetic in nature, and as a consequence, $J_2$ induces frustration owing to the in-plane triangular geometry of the Mn ions. $J_1$ is found to promote long-range antiferromagnetic order, while $J_2$ is responsible for spin canting and disorder. Our spin-wave analysis confirms that the system stabilizes a spin-spiral ground state with a propagation vector $q=(\frac{1}{6},\frac{1}{6},0)$, in agreement with neutron diffraction experiments. By tuning the $\frac{J_2}{J_1}$ ratio, we construct a phase diagram that reveals a transition from a collinear Néel antiferromagnetic state to spin-spiral phases with different propagation vectors and, eventually, to a disordered phase at large frustration. Atomistic spin dynamics simulations capture the temperature evolution of the magnetism and reproduce the experimentally measured magnetic specific heat as well as the transition temperature with good accuracy. Furthermore, for large $\frac{J_2}{J_1}$, we identify a low-temperature phase with slow spin relaxation and persistent fluctuations, suggesting a spin-liquid-like state. Our study provides a microscopic understanding of frustration-induced magnetism in ${\mathrm{CaMn}}_2{\mathrm{P}}_2$ and establishes it as a realization of the $J_1\text{−}{J}_2$ model in a three-dimensional lattice for exploring emergent magnetic phases.

Coupled-cluster and Green's function theories are highly successful in treating many-body electron correlation, and there has been significant interest in identifying and leveraging connections between them. Here we present a diagrammatic definition of the irreducible coupled-cluster self-energy that directly embeds coupled-cluster (CC) theory within the framework of many-body field theory. The equation-of-motion coupled-cluster (EOM-CC) treatment emerges naturally from our definition via the Dyson equation and the Bethe-Salpeter equation (BSE), providing a unified description of the random phase approximation (RPA), $GW$-BSE, and CC theory for ground state and excitation energies. This clarifies the origin of previously established connections between RPA, $GW$-BSE, and CC theory, and it exposes the relationship between vertex corrections and the coupled-cluster amplitude equations.

We theoretically investigate transport affected by cavity-mediated electron hopping in multiterminal quantum Hall bars, quantum point contacts, and Aharonov-Bohm interferometers. Beyond determining conductances and resistances, we analyze spatially resolved current distributions and local densities of states. Our study reveals how cavity-mediated interedge scattering impacts quantum magnetotransport in finite-size systems and how the cavity-mediated hopping significantly alters electron quantum interference effects.

The quantum geometric tensor is composed of the Berry curvature and the quantum metric, which is observable by means of optical absorption of elliptically polarized light. Especially, the quantum geometric tensor at the zero-momentum is observable by the optical absorption at the optical band edge. In this context, we study optical absorption of a $p$-wave magnet under irradiation of elliptically polarized light. The $p$-wave magnet has a band splitting along one axis, which we choose as the $x$ axis. We obtain exact analytic formulas for the optical conductivity when the Néel vector is along the $x$, $y,$ and $z$ axis. The optical conductivity strongly depends on the degree of ellipticity of light, which is an elliptic dichroism. Especially, there is a perfect elliptic optical dichroism when the Néel vector is along the $y$ axis. It is possible to determine the Néel vector by measuring the ellipticity of the perfect elliptic dichroism, which will be a key to future magnetic memory based on the $p$-wave magnet.

The interaction of a quantum system with its environment limits its coherence time. This, in particular, restricts the utility of qubits in quantum information processing applications. In this paper, we show that the decoherence of a coupled qubit system can be minimized, or even eliminated, by exploiting the quantum coherence of the bath itself. We investigate the dephasing in a system of two spatially separated, electronically decoupled qubits, with direct or mediated coupling, interacting with a shared bath. For illustration, we treat Förster or cavity-mediated coupling between semiconductor quantum dots interacting with acoustic phonons. Using the rigorous method of Trotter's decomposition with cumulant expansion, we demonstrate a reduction in the dephasing rates at specific distances between the dots. The control of dephasing with distance is a coherent effect of the shared bath and is absent for independent baths. It can be understood in terms of phonon-assisted transitions between the entangled qubit states of the coupled system.

The introduction of anisotropic media into non-Hermitian photonic systems provides novel means for manipulations with their exceptional points (EPs)—the singularities of degenerate eigenfrequencies and eigenmodes. In this paper, we propose a concept of double EPs appearing in the $\mathcal{PT}$-symmetric three-layer structures with the anisotropic middle layer. This becomes possible when the anisotropic medium optical axis lies out of the layers' plane. We show that the structure possesses two-sided reflectionlessness at the double EPs for one of the polarizations and has minimal transmission for the orthogonal polarization that can be used as a new approach to obtain polarized radiation. We study the dependence of double EPs' position on the system parameters demonstrating double EP stability with respect to the non-Hermiticity level and their tunability with respect to layer thicknesses and the anisotropy level. Moreover, the out-of-plane orientation of the optical axis can be considered as a general method to control positions and the number of EPs in non-Hermitian systems.

One of the most fascinating phenomena in non-Hermitian systems is the extensive accumulation of the bulk eigenstates under open boundary conditions known as the non-Hermitian skin effect (NHSE). Here, we propose a switchable NHSE in a topolectrical setup that can be turned on or off simply by varying the driving frequency without any modification to the physical circuit. Specifically, we consider a coupled system consisting of two non-Hermitian Hatano-Nelson chains where each node on one chain is connected to its neighboring nodes on the other chain via resistive couplings with opposite signs for the two coupling directions. Interestingly, the NHSE is switched on only if the driving frequency is greater than a certain critical frequency. Conversely, the NHSE in the coupled system is switched off when the frequency falls below the critical value, even though the individual uncoupled chains still exhibit the NHSE. This frequency-controlled NHSE may pave the way for many possible applications, including non-Hermitian sensors where the current and voltage localization can be manipulated through the driving frequency.

It was recently found that, going beyond the tenfold Altland-Zirnbauer symmetry classes and violating the bulk-boundary correspondence of the usual topological phases, $\mathcal{P}\mathcal{T}$-invariant systems support a real Chern insulator with the so-called boundary criticality, which forbids the transition between different orders of topological phases accompanied by the touching of bulk bands. Here, we find that periodic driving can break the boundary criticality of a $\mathcal{PT}$-invariant system. Upon setting the system free from the boundary criticality, diverse first- and second-order topological phases absent in the static case are found in both the zero and $\pi /T$ modes. In contrast to the usual Floquet ones defined on stroboscopic dynamics, our topological phases can only be characterized by the dynamical process of a whole driving period. The application of our result in a three-dimensional $\mathcal{PT}$-invariant system permits us to discover exotic second-order Dirac and nodal-line semimetals with coexisting surface and hinge Fermi arcs. Enriching the family of topological phases in $\mathcal{PT}$-invariant systems, our result provides a useful way to explore novel topological phases.

We present high-pressure electrical transport, magnetization, and single-crystal x-ray diffraction data on $\mathrm{SrC}{\mathrm{o}}_2{\mathrm{P}}_2$ single crystals, revealing a transition from the uncollapsed tetragonal (ucT) to the collapsed tetragonal (cT) phase >∼10 GPa. This structural transition is accompanied by ferromagnetic (FM) ordering with a Curie temperature up to 260 K. First-principles-based density functional theory calculations show that there is a first-order transition between ucT and cT phases, with an onset ∼10 GPa as well as the appearance of FM ordering in the cT phase. Above ∼30 GPa, the experimental signatures of the magnetic ordering vanish in a first-order-like manner, consistent with the theoretical calculation results, indicating that $\mathrm{SrC}{\mathrm{o}}_2{\mathrm{P}}_2$ is another example of the avoidance of quantum criticality in FM intermetallic compounds with almost room-temperature critical temperature. $\mathrm{SrC}{\mathrm{o}}_2{\mathrm{P}}_2$ provides clear evidence that the structural, electronic, and magnetic properties associated with the cT transition are strongly entangled and are not only qualitatively captured by our first-principles-based calculations but are quantitatively reproduced as well.

Long-range Coulomb forces give rise to correlated insulating states when charge particles populate a moiré superlattice at certain fractional filling factors. Such behavior is characterized by a broken translation symmetry wherein particles spontaneously form a Wigner crystal. Focusing on the experimental findings of Xu et al. [Nature (London) 587, 214 (2020)], we present a theory that captures the correlated insulating state of a fractionally filled moiré superlattice through the energy shift and change in oscillator strength of the exciton absorption resonance. The theory shows that the experimental findings can only be supported if the electrons reside in a charge-ordered state (i.e., electrons are not randomly distributed among the sites of the moiré superlattice). Furthermore, we explain why the energy shifts of exciton resonances are qualitatively different in cases where the superlattice is nearly empty compared with a superlattice whose sites are doubly occupied.

We study the Monte Carlo dynamics of strongly correlated classical particles coupled to lattice degrees of freedom in one-dimension relevant to the organic materials tetrathiafulvalene-chloranil (TTF-CA) and tetrathiafulvalene-bromanil (TTF-BA). These particles, carrying spin and subject to strong Coulomb repulsion, undergo a neutral-to-ionic transition as alternating site potentials decrease, leading to charge transfer to higher-energy sites. There is an enhancement of conductivity near the transition, carried by diffusive motion of thermally activated neutral-ionic domain walls (NIDWs). By including local lattice dimerization, we find that NIDW motion becomes subdiffusive and conductivity increases by an order of magnitude. These results underscore the crucial role of local and fluctuating dimerization in controlling transport and ferroelectric behavior near the neutral-ionic transition.