As many kagome metals, the topological superconductor ${\mathrm{AV}}_3{\mathrm{Sb}}_5$ with (A = K,Rb,Cs) hosts a charge density wave. A related chiral flux phase that breaks the time-reversal symmetry has been further theoretically predicted in these materials. The flux phase is associated with loop currents that produce ordered orbital magnetic moments, which would occur at the momentum points, $\mathbf{M}$, characterizing the charge-density wave state. Polarized neutron-diffraction experiments have been performed on an assembly of single crystals of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ to search for such orbital magnetic moments. No evidence for the existence of a three-dimensionally ordered moment is found at any temperature at the first ${\mathbf{M}}_1=(\mathrm{1/2},0,0)$ point in the Brillouin zone within an excellent experimental uncertainty, i.e., $\mathrm{m}=0\pm 0.01{\mu }_B$ per vanadium atom. However, the data might be suggestive of a putative magnetic orbital moment in the second Brillouin zone at ${\mathbf{M}}_{\mathbf{2}}=(\mathrm{1/2},\mathrm{1/2},0)$ at the detection limit of the experiment. Some loop currents patterns flowing only on vanadium triangles are able to account for this finding suggesting an ordered orbital magnetic moment of, at most, $\sim 0.02\pm 0.01{\mu }_B$ per vanadium triangle.

We report an experimental study of the magnetic properties of infinite-layer ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ ($x=0$ and 0.2) thin films by x-ray magnetic circular dichroism (XMCD) at Ni $L_{3,2}$ and Nd $M_{5,4}$ edges. We show the presence of a field induced out-of-plane ${\mathrm{Ni}}^{1+}$ spin moment, reaching values of $0.25{\mu }_B/\mathrm{Ni}$ at 9 T in the case of superconducting ${\mathrm{Nd}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_2$. The magnetic field and temperature dependencies of the Ni $L_{3,2}$ XMCD data can be explained by an out-of-plane canting of in-plane anti-ferromagnetically correlated ${\mathrm{Ni}}^{1+}$ spins. The canting is most likely attributed to the symmetry lowering of the ${\mathrm{NiO}}_2$ planes, observed via four-dimensional scanning transmission electron microscopy, which can trigger a Dzyaloshinskii-Moriya interaction among the ${\mathrm{Ni}}^{1+}$ spins.

We utilize density matrix renormalization group and fully augmented matrix product states (FAMPS) methods to investigate the valence bond solid (VBS) phase in the $J_1\text{−}{J}_2$ square lattice Heisenberg model. To differentiate between the columnar valence bond solid and plaquette valence bond solid (PVBS) phases, we introduce an anisotropy ${\mathrm{\Delta }}_y$ in the nearest-neighboring coupling in the $y$ direction, aiming at detecting the possible spontaneous rotational symmetry breaking in the VBS phase. In the calculations, we push the bond dimension to as large as $D=25000$ in FAMPS, simulating systems at a maximum size of $14\times 14$. With a careful extrapolation of the truncation errors and appropriate finite-size scaling, followed by finite ${\mathrm{\Delta }}_y$ scaling analysis of the VBS dimer order parameters, we identify the VBS phase as a PVBS type, meaning there is no spontaneous rotational symmetry breaking in the VBS phase. This paper not only supports the presence of PVBS order in the $J_1\text{−}{J}_2$ square lattice Heisenberg model, but also highlights the capabilities of FAMPS in the study of two-dimensional quantum many-body systems.

We study the formation and properties of perfectly flat zero-energy bands in a multilayer graphene system in the chiral limit. Employing the degrees of freedom of the multilayer system, such as relative twist-angle and relative shifts, in a way that preserves a set of symmetries, we define a two-dimensional parameter plane that hosts lines of two and four flat bands. This plane enables adiabatic continuation of a multilayer chiral system to weakly coupled bi- and trilayer systems, and through that mapping provides tools for calculating the Chern numbers of the flat bands. We show that a flat band of Chern number $C$ can be spanned by $C$ effective lowest Landau levels, all experiencing an effective flux of $1/C$ flux quantum per unit cell, and each carrying its own intra-unit-cell wave function. The flat bands do not disperse under the effect of a perpendicular magnetic field, and the gap to the dispersive bands closes when the externally applied flux cancels the $1/C$ effective flux.

The electronic structure of surfaces and interfaces plays a key role in the properties of quantum devices. Here, we study the electronic structure of realistic Al/InAs/Al heterojunctions using a combination of density functional theory with hybrid functionals and state-of-the-art quasiparticle $GW$ (QSGW) calculations. We find a good agreement between QSGW calculations and hybrid functional calculations, which themselves compare favorably well with angle-resolved photoemission spectroscopy experiments. Our paper confirms the need for well-controlled quality of the interfaces to obtain the needed properties of InAs/Al heterojunctions. A detailed analysis of the effects of spin-orbit coupling on the spin splitting of the electronic states shows a linear scaling in $k$ space, related to the two-dimensional nature of some interface states. The good agreement by QSGW and hybrid functional calculations opens the door towards trustable use of an effective approximation to QSGW for studying very large heterojunctions.

We investigated magnetotransport in mesoscopic samples containing electrons from three different subbands in GaAs triple wells. At high temperatures, we observed positive magnetoresistance, which we attribute to the imbalance between different types of particles that are sensitive to bulk viscosities. At low temperatures, we found negative magnetoresistance, attributed to shear viscosity. By analyzing the magnetoresistance data, we were able to determine both viscosities. Remarkably, the electronic bulk viscosity was significantly larger than the shear viscosity. Studying multicomponent electron systems in the hydrodynamic regime presents an intriguing opportunity to further explore the physics in systems with high bulk viscosity.

The possibility of selecting magnetic space groups by orienting the magnetization direction or tuning magnetic orders offers a vast playground for engineering symmetry-protected topological phases in magnetic materials. In this work, we study how selective tuning of symmetry and magnetism can influence and control the resulting topology in a two-dimensional magnetic system, and we illustrate such a procedure in the ferromagnetic monolayer ${\mathrm{MnPSe}}_3$. Density functional theory calculations reveal a symmetry-protected accidental semimetallic (SM) phase for out-of-plane magnetization, which becomes an insulator when the magnetization is tilted in-plane, reaching band-gap values close to 100 meV. We identify an order-2 composite antiunitary symmetry and threefold rotational symmetry that induce the band crossing, and we classify the possible topological phases using symmetry analysis, which we support with tight-binding and $\mathbf{k}·\mathbf{p}$ models. Breaking of inversion symmetry opens a gap in the SM phase, giving rise to a Chern insulator. We demonstrate this explicitly in the isostructural Janus compound ${\mathrm{Mn}}_2{\mathrm{P}}_2{\mathrm{S}}_3{\mathrm{Se}}_3$, which naturally exhibits Rashba spin-orbit coupling that breaks inversion symmetry. Our results map out the phase space of topological properties of ferromagnetic transition-metal phosphorus trichalcogenides, and they demonstrate the potential of the magnetization-dependent metal-to-insulator transition as a spin switch in integrated two-dimensional electronics.

We explore the effect of Ga substitution on the physical properties of single crystals of ${\mathrm{Ce}}_2{\mathrm{RhIn}}_8$ through measurements of temperature-dependent specific heat, magnetic susceptibility, and electrical resistivity. Our data on ${\mathrm{Ce}}_2{\mathrm{RhIn}}_{8-x}{\mathrm{Ga}}_x$, single crystals reveal a monotonic decrease of the antiferromagnetic transition temperature from $T_N=2.77$ K for the parent compound to $T_N$ = 1.96 K for the highest Ga concentration achieved ($x=0.55$). To understand the evolution of the crystalline electric field (CEF) scheme and exchange interactions as a function of Ga substitution, we fit our thermodynamic data to a Hamiltonian containing a tetragonal CEF term and mean-field isotropic exchange terms. Our results show a systematic increase in the energies of the first and second excited states as a function of Ga concentration. Moreover, we find significant changes to the CEF ground-state (GS) wave function ($\mathrm{\Gamma }=\alpha \mid \pm 5/2\rangle +\sqrt{1-{\alpha }^2}\mid \mp 3/2\rangle$), including an increase in the $\alpha$ coefficient and in the $\mid B_2^0\mid$ CEF parameter, with increasing Ga concentration. This evolution of the GS wave function drives the system away from the quantum critical point, whereas the chemical pressure associated with the Ga substitution drives the system towards it. Such behavior raises the question of whether pressure-induced superconductivity can be stabilized in this system. Our electrical resistivity and heat capacity measurements on ${\mathrm{Ce}}_2{\mathrm{RhIn}}_{7.64}{\mathrm{Ga}}_{0.36}$ under hydrostatic pressure reveal a zero-resistance state; however, no bulk superconductivity is detected. These results suggest that the occurrence of bulk superconductivity may be unfavorable in this system due to the observed CEF GS wave-function evolution and/or to the pair-breaking mechanism in the ${\mathrm{Ce}}_2{\mathrm{RhIn}}_{8-x}{\mathrm{Ga}}_x$ series.

The interplay and competition of topology and electron–electron interactions have fascinated researchers since the discovery of topological insulators. The Su–Schrieffer–Heeger–Hubbard (SSH-Hubbard) model is a prototypical model which includes both nontrivial topology and interactions. Due to its simplicity, there are several artificial quantum systems which can realize such a model to a good approximation. Here we focus on the quarter-filled case, where interactions and dimerization open a charge gap. In particular, we study the single-particle spectral function for the extended SSH-Hubbard model with magnetic field and explore several parameter limits where effective model descriptions arise. In the strongly dimerized limit, we show that the low-energy excitations of the spectral function resemble a half-filled Hubbard model with effective dimer sites and renormalized couplings. For strong magnetic field and interactions, we find physics akin to the spinless Su–Schrieffer–Heeger model at half filling, featuring a noninteracting topological phase transition. Moreover, in light of the recent realization of this model in quantum dot simulation, we provide evidence for the stability of the topological phase towards moderate nonlocal interactions in the experimentally expected parameter range.

In this paper, we theoretically study a class of three-dimensional (3D) nonliquid states that show exotic boundary phenomena in the thermodynamical limit. More concretely, we focus on a class of 3D fracton topological orders formed via stacking 2D twisted ${\mathbb{Z}}_N$ topologically ordered layers along $z$ direction. Nearby layers are coupled while maintaining translation symmetry along $z$ direction. The effective field theory is given by the infinite-component Chern-Simons (iCS) field theory, with an integer-valued symmetric block-tridiagonal Toeplitz $K$ matrix whose size is thermodynamically large. With open boundary conditions (OBC) along $z$, certain choice of $K$ matrices exhibits exotic boundary “Toeplitz braiding”, where the mutual braiding phase angle between two anyons at opposite boundaries oscillates and remains nonzero in the thermodynamic limit. In contrast, in trivial case, the mutual braiding phase angle decays exponentially to zero in the thermodynamical limit. As a necessary condition, this phenomenon requires the existence of boundary zero modes in the $K$-matrix spectrum under OBC. We categorize nontrivial $K$ matrices into two distinct types. Each type-I possesses two boundary zero modes, whereas each type-II possesses only one boundary zero mode. Interestingly, the integer-valued Hamiltonian matrix of the familiar 1D “Su-Schrieffer-Heeger model” can be used as a nontrivial $K$ matrix. Importantly, since large-gauge-invariance ensures integer quantized $K$-matrix entries, global symmetries are not needed to protect these zero modes. We also present numerical simulation as well as finite-size scaling, further confirming the above analytical results. Symmetry fractionalization in iCS field theory is also briefly discussed. Motivated by the present field-theoretical work, it will be interesting to construct 3D lattice models for demonstrating Toeplitz braiding, which is left to future investigation.

Recently, β-$\mathrm{Re}{\mathrm{O}}_2$ was theoretically proposed to be a candidate for Dirac nodal chain metal with hourglasslike energy-momentum dispersion and got considerable attention. Here, we have grown high-quality β-$\mathrm{Re}{\mathrm{O}}_2$ single crystals with a residual-resistivity ratio as large as 428. The magnetoresistance (MR) can reach 7 × ${10}^4\%$ measured under 9 T at 2 K. The fitting of MR and Hall data simultaneously by maximum entropy mobility spectrum reveals that there are two electron pockets and two hole pockets in β-$\mathrm{Re}{\mathrm{O}}_2$ with comparable carrier concentrations, which leads to the large unsaturated MR in β-$\mathrm{Re}{\mathrm{O}}_2$. Furthermore, we characterize the fermiology parameters of β-$\mathrm{Re}{\mathrm{O}}_2$ through de Haas–van Alphen (dHvA) effect studies at the high field up to 45.2 T. Aided by the Fermi surface (FS) calculated by first-principles, experimental dHvA analysis also substantiates the coexistence of two electron pockets and two hole pockets at the FS, which is in line with mobility spectrum analysis. Remarkably, the Landau fan diagram analysis for one of the electron pockets verifies the nontrivial Berry phase (≈0.87π) in β-$\mathrm{Re}{\mathrm{O}}_2$, suggesting that β-$\mathrm{Re}{\mathrm{O}}_2$ may be a topological material. In addition, in the high field (>20 T), we also probed signatures of Zeeman splitting, from which the Landé $g$ factors are extracted as ∼0.33–0.43. The detailed fermiology of β-$\mathrm{Re}{\mathrm{O}}_2$ provides valuable insights into the physical properties of other topological metals with similar characteristics.

Despite decades-long studies of how isotope-disorder scattering affects heat conduction, the effect of isotope-induced frequency shift on phonon-phonon interactions and lattice thermal transport remains largely unexplored and less understood. In this work, by using the phonon Boltzmann transport equation and machine-learning-assisted classical and path-integral molecular-dynamics simulations, we theoretically investigate the interplay between the intrinsic phonon-phonon scatterings and the isotopic compositions in lithium hydride (LiH). We reveal that the hydrogen isotopes notably impact thermal transport primarily via three-phonon interaction, while four-phonon scattering is less sensitive. Due to the stronger temperature dependence of higher-order processes, the isotope effect on thermal conductivity is increasingly suppressed by four-phonon scattering as temperature rises (from 73% to 35% at 700 K). In addition, we observe a more pronounced isotope effect on thermal diffusivity, which is attributed to the variation of heat capacity. Our work provides a promising avenue for manipulating thermal transport via isotope engineering, and it highlights the crucial role of four-phonon interaction.

In this study, we examine the behavior of the self-consistent order parameter in the presence of magnetic impurities and nanostructures on a superconducting surface. Using the Bogoliubov-de Gennes equations in a self-consistent lattice Green's function implementation, we reproduce the single-impurity behavior, where a strong interaction with the substrate can induce a $0-\pi$ transition, characterized by a local reversal in the sign of the order parameter. The presence of multiple impurities, forming structures such as spin chains, complicates the behavior of the order parameter. These impurities trigger quantum phase transitions, evident from changes in the ground-state quantum numbers, such as fermion parity. Overall, the order parameter serves as a valuable tool for confirming or refuting potential transitions, which can be challenging to analyze through numerical evaluations of the topological invariants alone.

This paper is devoted to a comprehensive theoretical study of asymmetric (skew) scattering in photonic graphene, with the main focus on its realization with semiconductor microcavity exciton-polaritons. As an important consequence of the skew scattering, we prove the appearance of the ratchet effect in this system. Triangular defects in the form of missing micropillars in a regular honeycomb lattice are considered to be ones that break the spatial inversion symmetry, thus providing the possibility of the ratchet effect. By means of the numerical solution of the effective Schrödinger equation, we provide microscopical insight into the process of skew scattering and determine indicatrices, cross sections, and asymmetry parameters. In a system with multiple coherently oriented triangular defects, a macroscopic ratchet effect occurs as a unidirectional flux upon noiselike initial conditions. Our study broadens the concept of ratchet phenomena in the field of photonics and optics of exciton-polaritons.

The tunneling valley Hall effect allows the electrical generation of the transverse valley-dependent current in tunnel junctions, which is free from the Berry curvature but requires tilted Dirac cones. Here, we propose a tilt-free mechanism to realize the tunneling valley Hall effect, based on the geometric-phase coherent transmission through two combined electric barriers in $\alpha \text{−}{\mathcal{T}}_3$ lattices. It is shown that the back-reflected electrons at the barrier interface may acquire a valley-dependent geometric phase. The coherence of this geometric phase leads to the valley-dependent skew tunneling, which is responsible for the transverse valley current. We further demonstrate that this transverse valley Hall current can be electrically controlled by the gate voltages applied across the two combined barrier regions and is absent when the two barriers are of equal height. Our work opens an approach to generating the valley Hall effect, suggesting potential applications for geometric-phase devices and valleytronic devices.

Recently, evidence of superconductivity (SC) has been reported in pressurized ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$. Here we study its possible pairing mechanism and pairing symmetry. Through fitting the density-functional-theory band structure, we provide a six-orbital tight-binding model. In comparison with the band structure of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, the additional nonbonding $d_{z^2}$ band is important to the pairing mechanism here. When the multiorbital Hubbard interactions are included, our random-phase-approximation based study yields an $s^{\pm }$-wave SC. The dominant Fermi-surface nesting with vector ${\mathbf{Q}}_1\approx (\pi ,\pi )$ is between the $\gamma$ pocket contributed by the bonding $d_{z^2}$ band top and the ${\alpha }_1$ pocket contributed by the nonbonding $d_{z^2}$ band bottom, leading to the strongest pairing amplitude and opposite gap signs within the two regimes. The dominant real-space pairing is the interlayer $d_{z^2}$-orbital pairing. This $s^{\pm }$-wave pairing pattern is insensitive to the band details. Upon electron doping, the $T_c$ would increase promptly before the system enters the Néel-ordered spin-density-wave phase.