Interaction-induced topological systems have attracted a growing interest for their exotic properties going beyond the single-particle picture of topological insulators. In particular, the interplay between strong correlations and finite doping can give rise to nonhomogeneous solutions that break the translational symmetry. In this paper, we report the appearance of a topological stripe state in an interaction-induced Chern insulator around half filling. In contrast to similar stripe phases in nontopological systems, here we observe the appearance of chiral edge states on top of the domain wall. Furthermore, we characterize their topological nature by analyzing the quantized transferred charge of the domains in a pumping scheme. Finally, we focus on aspects relevant to observing such phases in state-of-the-art quantum simulators of ultracold atoms in optical lattices. In particular, we propose an adiabatic state preparation protocol and a detection scheme of the topology of the system in real space.

Despite being an oxide, the delafossite ${\mathrm{PdCoO}}_2$ has an exceptionally high electrical conductivity that rivals those of the most conductive elemental metals, enabling a multitude of exotic transport phenomena. However, the reasons behind its unusually high electrical conductivity remained elusive for decades. Using first-principles transport calculations and theoretical modeling, we reveal that the ultrahigh electrical conductivity of ${\mathrm{PdCoO}}_2$ at room temperature originates from the contributions of both high Fermi velocities and exceptionally weak electron-phonon coupling, which leads to a coupling strength ($\lambda =0.057$) that is nearly an order of magnitude smaller than those of common metals. The abnormally weak electron-phonon coupling in ${\mathrm{PdCoO}}_2$ results from a low electronic density of states at the Fermi level, as well as the large and strongly facetted Fermi surface with suppressed Umklapp electron-phonon matrix elements. The insights gained from this work provide critical guidance for designing unconventional metals with superior electron transport properties.

We study a one-band Hubbard model of twisted bilayer cuprates with a twist angle of $53.{13}^{\circ }$. By introducing an interlayer bias, we simulate heterobilayers of different dopings. Using the variational cluster approximation, we probe the effect of this bias on the time-reversal symmetry-breaking (TRSB) phase. Doping differences between layers affect the region where TRSB occurs; we construct a phase diagram mapping out the TRSB phase in the $n_1-n_2$ plane, with $n_{\ell }$ being the electron density on layer $\ell$. We also map the spontaneous supercurrent on the same plane.

The many-body Green's function provides access to electronic properties beyond density-functional theory level in ab inito calculations. In this manuscript, we propose a deep learning framework for predicting the finite-temperature Green's function in atomic orbital space, aiming to achieve a balance between accuracy and efficiency. By predicting the self-energy matrices in Lehmann representation using an equivariant message-passing neural network, our method respects its analytical property and the $E\left(3\right)$ equivariance. The Green's function is obtained from the predicted self-energy through the Dyson equation with target total number of electrons. We present proof-of-concept benchmark results for both molecules and simple periodic systems, showing that our method is able to provide an accurate estimate of physical observables such as energy and density of states based on the predicted Green's function.

The pursuit of understanding the parity anomaly in condensed matter systems has led to significant advancements in both theoretical and experimental research in recent years. In this paper, we explore the parity anomaly of massless Dirac fermions in a semimagnetic topological insulator (TI) thin film subjected to a finite magnetic field. Our findings reveal an anomalous half-quantized Hall conductance arising from the occupied electronic states far below the Fermi level, which is directly associated with the parity anomaly. This observation demonstrates a crossover from one-half quantized Hall conductance in a metallic phase at zero field to one or zero quantized Hall conductance in the insulating phase at a strong field in the presence of disorders, serving as a key indicator for confirming parity anomaly. Our work provides valuable insights into the intricate relationship between band topology in condensed matter systems and quantum anomaly in quantum field theory.

We employ first-principles density-functional theory to perform a comparative investigation of the effect of the spin-orbit coupling (SOC) on the electronic and magnetic properties of three experimentally synthesized and characterized hexagonal perovskites ${\mathrm{Sr}}_{3}M{\mathrm{IrO}}_6$ $(M=\mathrm{Mg}, \mathrm{Zn}, \mathrm{Cd})$. The electronic-structure calculations show that in all compounds, Ir is the only magnetically active site in the $+4\left[5d^5\right]$ configuration, whereas $M^{+2}$ $(M=\mathrm{Cd}, \mathrm{Zn}, \mathrm{Mg})$ remains in nonmagnetic states with Cd/Zn and Mg featuring $d^{10}$ and $d^0$ electronic configurations, respectively. The insulating gap could be opened by switching on the correlation parameter $U$ for ${\mathrm{Sr}}_3{\mathrm{CdrO}}_6$ and ${\mathrm{Sr}}_3{\mathrm{ZnIrO}}_6$, which qualifies it to be a correlated Mott insulator. However, in the case of ${\mathrm{Sr}}_3{\mathrm{MgIrO}}_6$, both $U$ and antiferromagnetic ordering is not enough and the gap could only be opened by including the SOC, which classifies it to fall under the category of a typical SOC Mott insulator. The $j_{\text{eff}}$ states are visualized from the orbital-projected band structure. The magnetism is studied from the point of view of exchange interactions and magnetocrystalline anisotropy in the presence of the SOC. We also present the comparative analysis of the renormalized impact of SOC on the three compounds, which shows that all three compounds fall under the intermediate coupling regime, where ${\mathrm{Sr}}_3{\mathrm{MgIrO}}_6$ is comparatively closer to the atomic $j_{\text{eff}}=\frac{1}{2}$ picture from the others.

The multipartite entanglement structure for the ground states of two-dimensional (2D) topological phases is an interesting albeit not well-understood question. Utilizing the bulk-boundary correspondence, the calculation of tripartite entanglement in 2D topological phases can be reduced to that of the vertex state, defined by the boundary conditions at the interfaces between spatial regions. In this paper, we use the conformal interface technique to calculate entanglement measures in the vertex state, which include area-law terms, corner contributions, and topological pieces, and a possible additional order-one contribution. This explains our previous observation of the Markov gap $h=\frac{c}{3}ln2$ in the three-vertex state, and generalizes this result to the $p$-vertex state, general rational conformal field theories, and more choices of subsystems. Finally, we support our prediction by numerical evidence, finding precise agreement.

Optical properties in van der Waals heterostructures based on monolayer transition-metal dichalcogenides (TMDs) are often dominated by excitonic transitions. While intrinsic spin-orbit coupling (SOC) and an isotropic band structure are typically studied in TMDs, in their heterostructures Rashba SOC and trigonal warping (TW), resulting in bands with threefold anisotropy, are also present. By considering a low-energy effective Hamiltonian and Bethe-Salpeter equation, we study the effect of Rashba SOC and TW on the band structure and absorption spectra. Rashba SOC is predicted to lead to emergent excitons, which are identified as an admixture between $1s$ and $2p$ symmetries. In contrast, for experimentally relevant values, TW has only a negligible effect on the absorption spectrum. These findings could guide experimental demonstrations of emergent bright excitons and further studies of the proximity effects in van der Waals heterostructure.

Spontaneous Hall conductivity has recently been reported in the triangular lattice antiferromagnet ${\mathrm{Co}}_{1/3}\mathrm{Ta}{\mathrm{S}}_2$ under a zero magnetic field. This phenomenon originates from the distinctive noncoplanar triple-Q magnetic ground state, possessing uniform real-space Berry curvature characterized by scalar spin chirality. We investigated the physical properties of ${\mathrm{Co}}_{1/3}\mathrm{Ta}{\mathrm{S}}_2$ by judiciously controlling the composition, revealing a drastic change in its bulk properties, even by slight variations in cobalt composition, despite the same crystal structure. For $0.299\le x\le 0.325, {\mathrm{Co}}_x\mathrm{Ta}{\mathrm{S}}_2$ keeps all the characteristics of the ground state consistent with the previous studies—two antiferromagnetic phase transitions at $T_{\mathrm{N}1}$ and $T_{\mathrm{N}2}$ ($<T_{\mathrm{N}1}$), a large spontaneous Hall conductivity $\left[{\sigma }_{xy}\left(\mathbf{H}=0\right)\right]$, and a weak ferromagnetic moment along the $c$ axis. However, samples with $x\ge 0.330$ exhibit distinct bulk properties, including the absence of both ${\sigma }_{xy}\left(\mathbf{H}=0\right)$ and the weak ferromagnetic moment. Our neutron diffraction data reveal that ${\mathrm{Co}}_x\mathrm{Ta}{\mathrm{S}}_2$ with $x\ge 0.330$ develops coplanar helical magnetic order with ${\mathbf{q}}_{\mathrm{m}1}=$(1/3, 0, 0). This is entirely different from what has been seen in $x\le 0.325$, explaining the observed composition dependence.

Phonons as bosons are different from electrons as fermions. Unlike interatomic electron hopping that can be either positive or negative and further tuned by spin-orbit coupling, interatomic spring constant is positive, or the structure of atomic lattices would be dynamically unstable. Surprisingly, we found that topological phonon flat bands (FBs) can manifest either a positive or negative interatomic spring constant that couples the FB modes of opposite chirality, as exemplified by first-principles calculations of a 2D material of kagome boron nitride (BN). To reveal its physical origin, we first establish a fundamental correspondence between a collective lattice-coupling (CLC) variable of two quasiparticle states (e.g., electronic states or phonon modes) of opposite parity in a periodic lattice with band topology. Topological Dirac bands corresponds to a zero CLC at specific $k$ points (Dirac point) and topological gap of inverted bands corresponds to a negative CLC at a specific $k$ point, respectively. Then, we show topological FB has a special form of CLC that vanishes at all $k$ points as characterized by its real-space wave function, and multiatom FB phonon mode can manifest effectively a negative interatomic spring constant. Our findings shed light on our fundamental understanding of topology and provide a practical design principle for creating topological states.

We examine the response of the Fermi arc in the context of quasiparticle interference (QPI) with regard to a localized surface impurity on various three-dimensional Weyl semimetals (WSMs). Our study also reveals the variation of the local density of states (LDOS), obtained by Fourier transforming the QPI profile, on the two-dimensional surface. We use the $T$-matrix formalism to numerically (analytically and numerically) capture the details of the momentum space scattering in QPI (real-space decay in LDOS), considering relevant tight-binding lattice and/or low-energy continuum models modeling a range of different WSMs. In particular, we consider multi-WSM (mWSM), hosting multiple Fermi arcs between two opposite chirality Weyl nodes (WNs), where we find a universal $1/r$ decay ($r$ measuring the radial distance from the impurity core) of the impurity-induced LDOS, irrespective of the topological charge. Interestingly, the inter-Fermi arc scattering is only present for triple WSMs, where we find an additional $1/r^3$ decay as compared to double and single WSMs. The untilted single (double) [triple] WSM shows a straight line (leaf-like) [oval-shaped] QPI profile. The above QPI profiles are canted for hybrid WSMs where type-I and type-II Weyl nodes coexist; however, hybrid single WSM demonstrates strong nonuniformity, unlike the hybrid double and triple WSMs. We also show that the chirality and the positions of the Weyl nodes imprint marked signatures in the QPI profile. This allows us to distinguish between different WSMs, including the time-reversal-broken WSMs from the time-reversal-invariant WSM, even though both of the WSMs can host two pairs of Weyl nodes. Our study can thus shed light on experimentally obtainable complex QPI profiles and help differentiate different WSMs and their surface band structures.

In a class of periodically driven systems, multifractal states in nonequilibrium conditions and robustness of dynamical localization when the driving is made aperiodic have received considerable attention. In this paper, we explore a family of one-dimensional Aubry-André-Harper models that are quasiperiodically kicked with protocols following different binary quasiperiodic sequences, which can be realized in ultracold atom systems. The relationship between the systems' localization properties and the sequences' mathematical features is established utilizing the Floquet theorem and the Baker-Campbell-Hausdorff formula. We investigate the multifractality and prethermalization of the eigenstates of the unitary evolution operator combined with an analysis of the transport properties of initially localized wave packets. We further contend that the quasiperiodically kicked Aubry-André-Harper model provides a rich phase diagram as the periodic case but also brings the range of parameters to observe multifractal states and prethermalization to a regime more amenable to experiments.

Spontaneous and field-dependent spin switching (magnetization reversal) has been studied in the compensated ferrimagnet ${\mathrm{NdFeO}}_3$. The spin switching temperature $T_{\mathrm{sw}}$ monotonically approaches the compensation temperature $T_{\mathrm{comp}}$ with an increase in the applied magnetic field above $T_{\mathrm{comp}}\approx 9\mathrm{K}$. However, below $T_{\mathrm{comp}}$, a sharp drop in $T_{\mathrm{sw}}$ towards low temperatures and a simultaneous increase in the magnetization jump Δ$M$ at $T_{\mathrm{sw}}$ were found. The discontinuity in $T_{\mathrm{sw}}$ leads to two different $T_{\mathrm{sw}}–H$ phase lines shifted in opposite directions in temperature on the $T$–$H$ plane. These lines are described by two different spin switching energies. The same splitting in the switching energy of $600\mathrm{emu}{\mathrm{g}}^{-1}$ Oe follows directly from the magnetization jump data, and also coincides with the difference in unidirectional anisotropy energies for positive and negative exchange bias, both found near $T_{\mathrm{comp}}$. This indicates that the split spin switching energy, responsible for the anomaly in the $T$–$H$ diagram in ${\mathrm{NdFeO}}_3$, arises from the coexistence of two different exchange biases of opposite signs.

Magnetic frustration allows to access novel and intriguing properties of magnetic systems and has been explored mainly in planar triangular-like arrays of magnetic ions. In this work, we describe the phosphide ${\mathrm{Ce}}_6{\mathrm{Ni}}_6{\mathrm{P}}_{17}$, where the ${\mathrm{Ce}}^{+3}$ ions accommodate in a body-centered cubic lattice of ${\mathrm{Ce}}_6$ regular octahedra. From measurements of magnetization, specific heat, and resistivity, we determine a rich phase diagram as a function of temperature and magnetic field in which different magnetic phases are found. Besides clear evidence of magnetic frustration is obtained from entropy analysis. At zero field, a second-order antiferromagnetic transition occurs at $T_{N_1}\approx 1$ K followed by a first-order transition at $T_{N_2}\approx 0.45$ K. With magnetic field new magnetic phases appear, including a weakly first-order transition which ends in a classical critical point and a third magnetic phase. We also study the exact solution of the spin-1/2 Heisenberg model in an octahedron which allows us a qualitative understanding of the phase diagram and compare with the experimental results.

The spin wave is a promising candidate medium to be used as an information carrier and for processing. Knowledge of the spin wave dispersion relation is a prerequisite for its application and the design of devices. Here, we report on spin wave dispersion in perpendicularly magnetized synthetic antiferromagnets (p-SAFs), consisting of two CoFeB layers and a thin W spacer layer. The Brillouin light scattering technique is employed to measure the spin wave dispersion relations as a function of the in-plane magnetic field and wave vector. Two resonance modes are observed in the finite range of the magnetic field, in which the configuration of the magnetic moments in two CoFeB layers can be divided into antiferromagnetic and ferromagnetic states. In addition, we observe a T-type region, where the magnetization in one CoFeB layer lies in the direction of the in-plane magnetic field and the other stays in the out-of-plane direction. The dependences of the frequency on the wave vector demonstrate the spin wave propagation in this case is reciprocal. We also theoretically derive the spin wave dispersion relation for p-SAFs based on the Landau-Lifshitz equation, which agree well with the experimental results.

It is intriguing to explore the coexistence and (or) competition between charge density wave (CDW) and superconductivity (SC) in many correlated electron systems, such as cuprates [M. Hücker et al., Phys. Rev. B 83, 104506 (2011); Q. Li et al., Phys. Rev. Lett. 99, 067001 (2007), and J. Fink et al., Phys. Rev. B 79, 100502(R) (2009)], organic superconductors [Y. Ihara et al., Phys. Rev. B 100, 060505(R) (2019) and N. Morinaka et al., Phys. Rev. B 80, 092508 (2009)], and dichacolgenides [X. Xi et al., Nat. Nanotechnol. 10, 765 (2015) and J. A. Galvis et al., Phys. Rev. B 87, 094502 (2013)]. Among them, the recently discovered ${\mathbb{Z}}_2$ topological kagome metals $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A=\mathrm{K}$, Rb, Cs) serve as an ideal platform to study the intricate relation between them. Here, we report the electrical resistance measurements on ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ thin flakes ($\approx 60$ nm) under hydrostatic pressure up to 2.12 GPa to compare its pressure phase diagram of CDW and SC with its bulk form. Even though the CDW transition temperature ($T_{\mathrm{CDW}}$) in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ thin flakes is still monotonically suppressed under pressure and totally vanishes at $P_2=1.83$ GPa similar to the bulk, the superconducting transition temperature ($T_c$) shows an initial decrease and consequent increase up to its maximum $\sim 8.03$ K at $P_2$, in sharp contrast with the M-shaped double domes in the bulk ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. Our results suggest the important role of reduced dimensionality on the CDW state and its interplay with the SC, offering a new perspective to explore the exotic nature of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$.

Fe(Se,Te) is one of the simplest compounds of iron-based superconductors, but it shows a variety of vortex pinning phenomena both in thin-film and single-crystal forms. These properties are particularly important in light of its potential for applications ranging from the development of coated conductors for high-field magnets to topological quantum computation exploiting the Majorana particles found in the superconducting vortex cores. In this paper, we characterize the pinning properties of ${\mathrm{FeSe}}_{0.4}{\mathrm{Te}}_{0.6}$ single crystals, both pristine and Au-irradiated, with a set of characterization techniques ranging from the static limit to the GHz frequency range by using dc magnetometry, ac susceptibility measurements of both the fundamental and the third harmonic signals, and by microwave coplanar waveguide resonator measurements of London and Campbell penetration depths. We observed signatures of single vortex pinning that can be modeled by a parabolic pinning potential, dissipation caused by flux creep, and a general enhancement of the critical current density after 320 MeV Au ion irradiation.

We present a perturbative approach to disordered systems in one spatial dimension that accesses the full range of phase disorder and clarifies the connection between localization and phase information. We consider a long chain of identically disordered scatterers and expand in the reflection strength of any individual scatterer. We apply this expansion to several examples, including the Anderson model, a general class of periodic-on-average-random potentials, and a two-component discrete-time quantum walk, showing analytically in the latter case that the localization length can depend nonmonotonically on the strength of phase disorder (whereas expanding in weak disorder yields monotonic decrease). More generally, we obtain to all orders in the expansion a particular nonseparable form for the joint probability distribution of the transmission coefficient logarithm and reflection phase. Furthermore, we show that for weak local reflection strength, a version of the scaling theory of localization holds: the joint distribution is determined by just three parameters.