Quantum materials whose atoms are arranged on a lattice of corner-sharing triangles, i.e., the kagome lattice, have recently emerged as a captivating platform for investigating exotic correlated and topological electronic phenomena. Here, we combine ultralow temperature angle-resolved photoemission spectroscopy (ARPES) with scanning tunneling microscopy and density functional theory calculations to reveal the fascinating electronic structure of the bilayer-distorted kagome material $Ln{\mathrm{Ti}}_3{\mathrm{Bi}}_4$, where Ln stands for Nd and Yb. Distinct from other kagome materials, $Ln{\mathrm{Ti}}_3{\mathrm{Bi}}_4$ exhibits twofold, rather than sixfold, symmetries, stemming from the distorted kagome lattice, which leads to a unique electronic structure. Combining experiment and theory we map out the electronic structure and discover double flat bands as well as multiple Van Hove singularities (VHSs), with one VHS exhibiting higher-order characteristics near the Fermi level. Notably, in the magnetic version ${\mathrm{NdTi}}_3{\mathrm{Bi}}_4$, the ultralow base temperature ARPES measurements unveil an unconventional band splitting in the band dispersions which is induced by the ferromagnetic ordering. These findings reveal the potential of bilayer-distorted kagome metals $Ln{\mathrm{Ti}}_3{\mathrm{Bi}}_4$ as a promising platform for exploring novel emergent phases of matter at the intersection of strong correlation and magnetism.

We focus on the biorthogonal work statistics of the interacting many-body Hatano-Nelson model after switching on the imaginary vector potential. We introduce a generalized Loschmidt echo $G\left(t\right)$ using the biorthogonal metric operator whose Fourier transform yields the probability distribution of work done. The statistics of work displays several universal features, including an exponential decay with the square of both the system size and imaginary vector potential for the probability to stay in the ground state. Additionally, its high-energy tail follows a universal power law with exponent $-3$. This originates from the peculiar temporal power-law decay of $G\left(t\right)$ with a time-dependent exponent, corresponding to an unusual orthogonality catastrophe. The mean and the variance of work scale linearly and logarithmically with system size, while all higher cumulants are nonextensive. Our results are relevant for nonunitary field theories as well.

In twisted bilayer semiconductors with arbitrary twisting angles, a chiral excitonic system can arise from the interlayer electron-hole Coulomb exchange interaction (Förster coupling) that hybridizes the anisotropic intralayer excitons from individual layers. We present a general framework for the effective exciton Hamiltonian taking into account the electron-hole Coulomb exchange, using twisted homobilayer systems composed of transition metal dichalcogenides or black phosphorus as examples. We demonstrate that such chiral excitonic systems can feature unconventional Hall (Nernst) effects arising from quantum geometric properties characteristic of the layer hybridized wave functions under the chiral symmetry, for example, the time-reversal even-layer Hall counterflow and the crossed nonlinear dynamical Hall effect, when mechanical and statistical force (temperature or density gradient) drives the exciton flow.

The Wannier-Stark localization dynamically alters the entanglement behavior of non-Hermitian free fermions. Utilizing the single-particle correlation matrix technique, we analyze the effective Hamiltonian of these fermions with a Wannier-Stark ladder. Under open boundary conditions, we observe steady-state half-chain entanglement entropy (EE) and identify two distinct area-law regions and an algebraic scaling region. Finite-sized scaling analysis reveals critical scaling behavior of the half-chain EE. Notably, the system demonstrates unique entanglement characteristics under periodic boundary conditions, which diverge from the $(1+1)d$ conformal field theory predictions for Anderson localization. Our findings highlight entanglement phases emerging from the interplay between the non-Hermitian skin effect and disorder-free localization.

The low lattice thermal conductivity in tin selenide is key to its excellent thermoelectric properties. The dominant mechanism for this phononic property, however, is debated. Past lattice-dynamic calculations for SnSe consistently predicted the existence of a phonon bandgap, which is puzzling as it has not been observed in spectroscopic experiments and is typically associated with low phonon-scattering rates in contrast to the observed physical properties. In this work, we accurately investigate the size of the phonon bandgap in SnSe using a direct comparison between experimental neutron spectroscopy, lattice-dynamic calculations, and $abinitio$ molecular dynamics. We theoretically investigate the effects of van der Waals interactions in density functional theory calculations using the popular Grimme D2/D3 and semilocal methods and we also assess the effect of finite-temperature driven anharmonicity using Born-Oppenheimer $abinitio$ molecular dynamics. The D2/D3 lattice dynamics calculations, which assume 0 K, predict a phonon bandgap, although the size and structure depends on the details of the van der Waals correction. In contrast, both the experiment and $abinitio$ dynamics identify there is a valley in the density of states at finite temperature, ascribed to strong anharmonicity that shifts specific phonon modes. This finding highlights the need for great care when applying 0 K lattice dynamics and dispersion corrections to SnSe, with general implications for designing thermoelectric materials via computational methods.

Heterostructures comprising of ferromagnet and nonmagnetic metal (NM) interfaces capable of generating spin torque are crucial for next-generation ultrafast magnetic switching devices. Here we present the effect of change of NM underlayer with different spin-orbit coupling (SOC) strength on the spin-dependent electronic structure of quintessential heterostructures of CoFeB/NM. The results reveal deviations from the conventional expectation of the dependence on the strength of SOC of the NM layer. Dichroic photoemission measurements indicate that the spin polarization of the ferromagnetic CoFeB layer is higher with the weaker-SOC Cu underlayer than that with the stronger-SOC Ta, Pt, and W underlayers. The phase space of the unoccupied electronic states near the Fermi level is found more for the W underlayer system than that of the Cu and Ta underlayer systems.

We study the anomalous Hall effect arising from the altermagnetic order and spin-orbit interaction in doped ${\mathrm{FeSb}}_2$. To investigate the anomalous transport, we have constructed a tight-binding model of ${\mathrm{FeSb}}_2$. We separately considered the constraints imposed on the model parameters by the spin symmetry group and magnetic symmetry group at zero and finite spin-orbit interaction, respectively. The resulting model includes the effect of exchange splitting and is applicable at both zero and finite spin-orbit interaction. In the case of spin symmetry, the analysis covers the spin-only subgroup arising from collinear magnetism, as well as nontrivial symmetry elements. This allows us to explore changes in the hopping amplitudes as symmetry is reduced by spin-orbit interaction from the spin group to the magnetic group. While the anomalous Hall effect is forbidden by spin symmetry, it is allowed by the symmetries of the magnetic group. The intrinsic Hall conductivity is shown to vanish linearly with spin-orbit interaction. This nonanalytic behavior is universal to altermagnets. It originates from the singularity of the Berry curvature localized along lines on a Fermi surface confined to symmetry planes. These planes host spin degeneracy protected by spin symmetry, which is lifted by spin-orbit interaction.

Magnetotransport is often employed as an effective method to study the underlying quantum correction to classical Drude conductivity. Here, we report a rare cooperative correction phenomenon arising from both spin-singlet and spin-triplet channels, which is manifested by the coexistence of weak antilocalization (WAL) effects induced by strong spin-orbit coupling (SOC) of Pt and weak localization (WL) effects due to the Pt spontaneous magnetization in the $\mathrm{Pt/V}{\mathrm{I}}_3$ heterostructures. The magnetoresistance exhibits an unexpected field-independent response at low magnetic fields, which cannot be explained by traditional Lorentz scattering theory or interpreted as a cusplike WAL response. The anomalous Hall signal observed in the heterostructures indicates the emergence spontaneous magnetizations in Pt, and the density functional theory calculations confirm that SOC of Pt at the interface of heterostructures remains robust. Consequently, we reasonably deduce that the unusual magnetotransport behavior fundamentally originates from the quantum cooperative correction of WAL and WL in the heterostructures. However, it proposes a huge challenge for realizing quantum coexistence of two distinct symmetric channels in real materials, thereby highlighting the potential of artificial heterostructures in constructing complex electronic structures and multifunctional electronic devices.

Identifying superconducting materials with spin-polarized Cooper pairs is an important objective both for exploration of new fundamental physics and for cryogenic applications in spintronics and quantum sensing. We here compute the critical temperature $T_c$ of the superconducting transition in a bilayer composed of a superconductor with an intrinsic spin-triplet order parameter and a ferromagnet. We determine how $T_c$ varies both with the thickness of the ferromagnet and its magnetization direction. We show that both the orbital and spin part of the triplet superconducting order parameter leave clear signatures in $T_c$ which do not appear in a bilayer of a conventional $s$-wave superconductor and a ferromagnet. In particular, the dependence of $T_c$ on these variables changes depending on whether or not the superconducting order parameter features Andreev bound states and also changes qualitatively when the magnetization is rotated in the plane of the ferromagnetic film. We also show that a single-component triplet order parameter, such as $p_y$-wave, can have a strong enhancement near a boundary due to the Friedel oscillations causing an energy-dependent modulation of the local density of states. Measurements of $T_c$ in such bilayers are therefore useful to identify the pairing symmetry of intrinsic triplet superconductors.

Quasiperiodicity has recently been proposed to enhance superconductivity and its proximity effect. Simultaneously, there has been significant experimental progress in the fabrication of quasiperiodic structures, including in reduced dimensions. Motivated by these developments, we use microscopic tight-binding theory to investigate the DC Josephson effect through a ballistic Fibonacci chain attached to two superconducting leads. The Fibonacci chain is one of the most-studied examples of quasicrystals, hosting a rich multifractal spectrum, containing topological gaps with different winding numbers. We study how the Andreev-bound states (ABS), current-phase relation, and the critical current depend on the quasiperiodic degrees of freedom, from short to long junctions. While the current-phase relation shows a traditional $2\pi$ sinusoidal or sawtooth profile, we find that the ABS develop quasiperiodic oscillations and that the Andreev reflection is qualitatively altered, leading to quasiperiodic oscillations in the critical current as a function of junction length. Surprisingly, despite earlier proposals of quasiperiodicity enhancing superconductivity compared to crystalline junctions, we do not, in general, find that it enhances the critical current. However, we find significant current enhancement for reduced interface transparency because of the modified Andreev reflection. Furthermore, by varying the chemical potential, e.g., by an applied gate voltage, we find a fractal oscillation between superconductor-normal metal-superconductor (SNS) and superconductor-insulator-superconductor (SIS) behavior. Finally, we show that the winding of the subgap states leads to an equivalent winding in the critical current, such that the winding numbers, and thus the topological invariant, can be determined.

While spin-triplet pairing remains elusive in nature, there is a growing effort to realize proximity-induced equal-spin triplet superconductivity in junctions with magnetic regions or an applied magnetic field and common $s$-wave superconductors. To enhance such spin-triplet contribution, it is expected that junctions with a weak interfacial barrier and strong spin-orbit coupling are desirable. Intuitively, a weak interfacial barrier enables a robust proximity-induced superconductivity and strong spin-orbit coupling promotes spin mixing, converting spin-singlet into spin-triplet superconductivity. In contrast, we reveal a nonmonotonic spin-triplet contribution with the strength of the interfacial barrier and spin-orbit coupling. This picture is established by considering different signatures in conductance and superconducting correlations, as well as by performing self-consistent calculations. As a result, we identify a strongly enhanced spin-triplet superconductivity, realized for an intermediate strength of interfacial barrier and spin-orbit coupling. In junctions with magnetic regions, an enhanced spin-triplet superconductivity leads to a large magnetoanisotropy of conductance and superconducting correlations. This picture of an enhanced spin-triplet superconductivity is consistent with experiments demonstrating a huge increase in the conductance magnetoanisotropy, which we predict can be further enhanced at a finite bias.

The ground state of second-quantized quantum chemistry Hamiltonians provides access to an important set of chemical properties. Wave functions based on machine-learning architectures have shown promise in approximating these ground states in a variety of physical systems. In this paper, we show how to achieve state-of-the-art energies for molecular Hamiltonians using the the neural network backflow (NNBF) wave function. To accomplish this, we optimize this ansatz with a variant of the deterministic optimization scheme based on selected configuration interaction introduced by Li et al., [J. Chem. Theory Comput. 19, 8156 (2023)], which we find works better than standard Markov chain Monte Carlo sampling. For the molecules we studied, NNBF gives lower energy states than both Coupled Cluster with Single and Double excitations and other neural network quantum states. We systematically explore the role of network size as well as optimization parameters in improving the energy. We find that, while the number of hidden layers and determinants play a minor role in improving the energy, there are significant improvements in the energy from increasing the number of hidden units as well as the batch size used in optimization, with the batch size playing a more important role.

We report a viable strategy to realize topological flat bands in one-dimensional armchair graphene antidot lattices. The quantum destructive interference effect leads to largely quenched intra-antidot hopping with nearly zero values, creating flat bands with a nontrivial topology, as unveiled by an effective Su-Schrieffer-Heeger model under extreme conditions. As a proof of concept, we demonstrate our approach in the on-surface synthesized porous seven-carbon-wide armchair graphene nanoribbons with periodic divacancy-type antidots, and showcase the robust flatness of the designer topological flat bands with a high tunability through strain and structural engineering which are investigated by combining tight-binding and density functional theory calculations with scanning probe microscopy measurements. We show that such available one-dimensional graphene nanoribbons can provide a rich platform for exploiting novel physics at the confluence of strong correlation and topology, opening up new avenues for research in the field of topological materials and their potential applications in quantum devices.

Optical cavities are widely used to induce strong light-matter coupling and thereby enable the presence of polaritons. While polaritons are at the source of most of the observed physics, the mirrors forming the cavity may also themselves be responsible for a number of phenomena, independently of the strong light-matter coupling regime. Here we use a toy model of a chain of dipolar emitters coupled to a cuboidal cavity. We unveil several effects originating solely from the boundary conditions imposed by the cavity mirrors, that are dominant when the distances of the emitters to the cavity walls are of the order of the interdipole separation. In particular, we show that mirrors in the direction transverse to the chain may act as effective defects, leading to the emergence of Tamm edge states. Considering a topological chain, we demonstrate that such transverse mirrors may also protect edge states against the effects of the strong light-matter coupling. Finally, we find that mirrors parallel to the chain, by the image charges they involve, induce topological phase transitions even in the case of highly off-resonant photons.

We consider an extended trimer Su-Schrieffer-Heeger (SSH) tight-binding Hamiltonian keeping up to next-nearest-neighbor (NNN)-hopping terms and on-site potential energy. The Bloch Hamiltonian can be expressed in terms of all the eight generators (i.e., Gell-Mann matrices) of the SU(3) group. We provide exact analytical expressions of three dispersive energy bands and the corresponding eigenstates for any choices of the system parameters. The system lacks full chiral symmetry since the energy spectrum is not symmetric around zero, except at isolated Bloch wave vectors. We explore parity, time reversal, and certain special chiral symmetries for various system parameters. We discuss the bulk-boundary correspondence by numerically computing the Zak phase for all the bands and the boundary modes in the open boundary condition. There are three different kinds of topological phase transitions, which are classified based on the gap closing points in the Brillouin zone (BZ) while tuning the nearest-neighbor (NN)- and NNN-hopping terms. We find that quantized changes (in units of $\pi$) in two out of three Zak phases characterize these topological phase transitions. We propose another bulk topological invariant, namely the sublattice winding number, which also characterizes the topological phase transitions changing from ${\nu }^{\alpha }=0\leftrightarrow 2$ and ${\nu }^{\alpha }=0\leftrightarrow 1\leftrightarrow 2$ ($\alpha$: sublattice index). The sublattice winding number not only provides a relatively simple analytical understanding of topological phases but also successfully establishes bulk-boundary correspondence in the absence of inversion symmetry, which may help in characterizing the bulk-boundary correspondence of systems without chiral and inversion symmetry.

We analytically investigate the plasmons propagating in a homogeneous two-dimensional (2D) electron system, along the metal grating in the form of a periodic array of strip-shaped electrodes (gates) in the vicinity of the 2D system. We show that in the case of semi-infinite grating, the Tamm plasmon modes localized near and propagating along the grating edge can exist in the gaps of the plasmonic band structure provided that the last gate differs in width from the other gates. When the last gate is wider, the spectrum of the fundamental Tamm plasmon mode lies in the lowest frequency gap, below the first plasmonic band. Importantly, we find the mode to exist in this case only for finite values of the wave vector along the grating. Otherwise, if the width of the last gate is smaller, the Tamm plasmon modes occupy higher frequency gaps, and delocalized plasmons from the first frequency band become the lowest frequency excitations.

Systems with conserved dipole moment have drawn considerable interest in light of their realization in recent experiments on tilted optical lattices. An important issue regarding such systems is delineating the conditions under which they admit a unique gapped ground state that is consistent with all symmetries. Here, we study one-dimensional translation-invariant lattices that conserve $\mathrm{U}\left(1\right)$ charge and ${\mathbb{Z}}_L$ dipole moment, where discreteness of the dipole symmetry is enforced by periodic boundary conditions, with $L$ the system size. We show that in these systems a symmetric, gapped, and nondegenerate ground state requires not only integer charge filling, but also a fixed value of the dipole filling, while other fractional dipole fillings enforce either a gapless or symmetry-breaking ground state. In contrast with prior results in the literature, we find that the dipole filling constraint depends both on the charge filling as well as the system size, emphasizing the subtle interplay of dipole symmetry with boundary conditions. We support our results with numerical simulations and exact results.

Higher-order topological insulators harbor unique corner modes that hold immense potential for applications in information storage. However, the practical manipulation of these states has been constrained by the fixed positions and energies of conventional corner modes. In this Letter, we present a theoretical framework for generating topologically protected cornerlike modes in higher-order topological insulators, exhibiting unprecedented tunability in their positions. These cornerlike modes are characterized by a quantized generalized quadrupole moment, indicative of the presence of fractional charges. Moreover, we demonstrate the remarkable ability to modulate the energy of these topological corner modes. Our findings pave the way for the controlled manipulation of corner modes in higher-order topological insulators, opening up different avenues for their applications in advanced information technologies.

We discover a family of local deformations that leave part of the spectrum intact for strongly interacting and exactly solvable quantum many-body systems. Since the deformation preserves the Bethe ansatz equations (BAE), it is dubbed the iso-BAE flow. Although all theories on the flow share the same BAE, the spectra are different. Part of the spectrum remains intact along the whole flow. Such states are protected by an emergent symmetry. The remaining parts of the spectrum change continuously along the flow and are doubly degenerate for even-length spin chains. For odd-length chains, the deformed spectrum also comprises doubly degenerate pairs apart from the sector with magnon number $(L+1)/2$, where $L$ is the length of the spin chain. We discuss the iso-BAE flow for the ${\mathrm{XXX}}_{1/2}$ model in detail and show that the iso-BAE flows exist for more general models including $q$-deformed XXZ as well as higher-spin ${\mathrm{XXX}}_s$ spin chains.

Recently, a photonic alloy with nontrivial topological properties has been proposed, based on the random mixing of yttrium iron garnet (YIG) and magnetized YIG rods. When the doping concentration of magnetized YIG rods is less than one, a chiral edge state (CES) of the topological photonic alloy appears in the frequency range of the nontrivial topological gap of the magnetized YIG crystal. In this work, we surprisingly find that by randomly mixing the perfect electric conductor (PEC) and magnetized YIG rods in a square lattice, the photonic alloy system with appropriate doping concentrations can present CES in special frequency intervals even when both components support the propagation of bulk states. Analyzing the band structure of two components, we noticed a shift between the first trivial band gap for PEC and the first topological band gap for magnetized YIG. When calculating the transmission spectrum of the photonic alloy, we discovered that the frequency range for the topological gap gradually opens from the lower limit frequency of the band gap for PEC to the band gap for the magnetized YIG rods. The topological gap opening occurs as the doping concentration of magnetized YIG rods increases, creating an effective band-alignment effect. Moreover, the topological gap for the photonic alloy is confirmed by calculating the reflection phase winding with the scattering method. Lastly, the gradual appearance of the CES is identified by applying Fourier transformation to real-space electromagnetic fields. Our work broadens the possibilities for flexible topological-gap engineering in the photonic alloy system.