Within linear response theory, the absorptive part of highly anisotropic optical conductivities are analytically calculated for distinct tilts in two-dimensional (2D) tilted semi-Dirac bands (SDBs). The transverse optical conductivities always vanish. The interband longitudinal optical conductivities (LOCs) in 2D tilted SDBs differ qualitatively in the power-law scaling of $\omega$ as $\mathrm{Re}{\sigma }_{\perp }^{\mathrm{IB}}\left(\omega \right)\propto {\sigma }_0\sqrt{\omega }$ and $\mathrm{Re}{\sigma }_{\parallel }^{\mathrm{IB}}\left(\omega \right)\propto {\sigma }_0/\sqrt{\omega }$. By contrast, the intraband LOCs in 2D tilted SDBs depend on $\mu$ in the power-law scaling as $\mathrm{Re}{\sigma }_{\perp }^{\mathrm{D}}\left(\omega \right)\propto {\sigma }_0\mu \sqrt{\mu }$ and $\mathrm{Re}{\sigma }_{\parallel }^{\mathrm{D}}\left(\omega \right)\propto {\sigma }_0\mu /\sqrt{\mu }$. The tilt-dependent behaviors of LOCs could qualitatively characterize distinct impact of band tilting in 2D tilted SDBs. In particular, for arbitrary tilt $t$ satisfying $0<t\le 2$, the interband LOCs always possess a robust fixed point at $\omega =2\mu$. The power-law scalings and tilt-dependent behaviors further dictate significant differences in the asymptotic background values and angular dependence of LOCs. Our theoretical predictions should be valid for a broad class of 2D tilted SDB materials, and can also be used to fingerprint 2D tilted SDB from 2D untilted SDB as well as tilted Dirac bands.

We report the existence of a nondecaying circular spin current in an antiferromagnetic (AFM) quantum ring with zero net magnetization. In the presence of a finite voltage bias, a net circular spin current is generated in the ring geometry without accompanying any charge current. Such a bias-driven pure spin circular current in a magnetic ring with vanishing net magnetization has not been reported so far to the best of our knowledge. Employing a tight-binding framework to describe the nanojunction which is formed by connecting the AFM ring with two electrodes, we compute spin-dependent transport quantities along with spin circular current using the standard Green's function formalism. Most of the results are analyzed for the AFM ring where neighboring magnetic moments are arranged in antiparallel directions and different other configurations of magnetic moments are also taken into account for comparison. Various aspects are critically discussed like ring-electrode interface sensitivity, impurities at different lattice sites, ring-electrode coupling strength, spin-dependent scattering factor, Fermi energy, and system size, to make the present communication a self-contained one. For some input conditions, a nonzero circular charge current may appear but that is too small compared to the spin circular current. All the results are valid for a wide range of physical parameters which proves the robustness of the phenomenon of bias-driven circular spin current in an AFM nanoring. In the end, we also provide experimental perspectives for designing AFM ring systems. Our analysis red paves the way for obtaining a pure spin current in open quantum systems, offering opportunities to explore various simple and complex AFM loop substructures in the presence of external baths.

Broken spatial inversion symmetry in semiconducting materials with time-reversal pair valleys can exhibit valley polarization. Based on first-principles calculations, here we propose a lateral heterostructure of a kagome lattice of $h\text{−}\mathrm{BN}$ and hexagonal graphene domains that exhibits opposite Berry curvature in inequivalent $\mathbf{K}$ and ${\mathbf{K}}^{\prime }$ valleys. Explicit consideration of the excitonic scattering processes within the $GW$ and Bethe-Salpeter equation formalism confirm insignificant intervalley coupling and consequent valley-polarization ability along with a 0.46 eV higher binding energy of triplet excitons. Such a heterostructure with a large charge carrier mobility can be exploited for advanced valleytronic and optoelectronic applications.

The properties of stable Luttinger liquid phases in models with a nonconserved number of particles are investigated. We study the Luttinger liquid phases in one-dimensional models of hard-core boson and spinless fermion chains where particles can be created and annihilated three by three on adjacent sites. We provide an intuitive and systematic method based on the flow equation approach, which accounts for additional terms in the correlations generated by the ${\mathbb{Z}}_3$-symmetric interactions. We find that despite the emergence of U(1) symmetry under renormalization, the observables are still affected by its breaking in the bare Hamiltonian. In particular, the standard bosonization mapping becomes insufficient to capture the full behavior of correlation functions.

We study the effect of the off-diagonal elements of the Wannier Hamiltonian on the electronic structure of the low-symmetry material ${\mathrm{Li}}_2{\mathrm{MnO}}_3$ ($C2/m$), using dynamical mean field theory calculations with a continuous-time quantum Monte Carlo impurity solver. The presence of significant off-diagonal elements leads to a pronounced suppression of the energy gap. The off-diagonal elements are largest when the Wannier projection is used based on the global coordinate, and they remain substantial even with the projection using the local coordinate close to the direction of Mn-O bonds. We show that the energy gap is enhanced by the diagonalization of the Mn $d$ block in the full $p\text{−}d$ Hamiltonian with the application of a unitary rotation matrix. Additionally, the inclusion of small double counting energy is crucial for achieving the experimental gap by reducing $p\text{−}d$ hybridization. Furthermore, we establish the efficiency of a low-energy ($d$-only basis) model for studying the electronic structure of ${\mathrm{Li}}_2{\mathrm{MnO}}_3$, as the Wannier basis represents a hybridized state of Mn $d$ and O $p$ orbitals. These findings suggest an appropriate approach for investigating low-symmetry materials using the density functional theory plus dynamical mean field theory ($\mathrm{DFT}+\mathrm{DMFT}$) method. We also find that the antiferromagnetic ground state ${\mathrm{\Gamma }}_{2u}$ is stable with $U\le 2\mathrm{eV}$ within density functional theory$+U$ calculations, which is much smaller than the widely used $U=5\mathrm{eV}$.

The parton approach for quantum spin liquids gives a transparent description of low-energy elementary excitations, e.g., spinons and emergent gauge-field fluctuations. The latter ones are directly coupled to the hopping/pairing of spinons. By using the fermionic representation of the $U\left(1\right)$ Dirac state on the kagome lattice and variational Monte Carlo techniques to include the Gutzwiller projection, we analyze the effect of modifying the gauge fields in the spinon kinematics. In particular, we construct low-energy monopole excitations, which are shown to be gapless in the thermodynamic limit. States with a finite number of monopoles or with a finite density of them are also considered, with different patterns of the gauge fluxes. We show that these chiral states are not stabilized in the Heisenberg model with nearest-neighbor superexchange couplings, and the Dirac state corresponds to the lowest-energy ansatz within this family of variational wave functions. Our results support the idea that spinons with a gapless conical spectrum coexist with gapless monopole excitations, even for the spin-1/2 case.

Based on our proposed layer-by-layer integrating method, the elastic modulus of an arbitrary inclined connection unit of two grains is derived. Furthermore, the derived formula is extended to the multibody connection of polycrystalline grains. Then, the derived formulae are verified by the finite element method and the experimental results available. Finally, an efficient software program is developed based on the derived formula to predict the elastic moduli of polycrystalline materials through the orientation measurement by electron backscatter diffraction, which is consistent with related experimental data. This work provides a simple method and software to predict accurately the elastic modulus of polycrystalline materials.

In this study, we establish circuit-theoretical bulk-edge correspondences to indicate the existence of surface plasmon polaritons topologically. First, we reveal an essential topological transition in a minimal circuit model of a composite right-/left-handed transmission line. We then demonstrate that the circuit model can accurately explain the dielectric-metal transition. Using mirror symmetry and Foster's reactance theorem, we prove a parity-reactance correspondence that relates the parities of the bulk wave functions to the sign of the surface reactance. The parity-reactance correspondence describes the underlying mechanism of surface-plasmon-polariton formation without focusing on the Zak phase. Zero flat bands play an essential role in this mechanism, allowing us to define a topological integer that classifies the direct-current (DC) response. The conventional surface-reactance formula using the Zak phase requires plasmonic modification by the defined topological integer. Finally, we develop alternative bulk-edge correspondences based on the DC response without invoking mirror symmetry.

Magnetic Weyl semimetals can reveal a renowned electronic transport phenomenon, i.e., the anomalous Hall effect due to the intrinsic Berry curvature promoted by the Weyl fermions. Here, the layered kagome compound ${\mathrm{Rh}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ is identified as a ferromagnetic Weyl semimetal by first-principles calculations. When the spin-orbit coupling is absent, three sets of nontrivial Weyl nodal lines emerge in the spin-up channel, while the spin-down bands are fully gapped. The obtained magnetocrystalline anisotropy energy indicates that ${\mathrm{Rh}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ has an in-plane canted magnetic order with a ${30}^{\circ }$ angle to the $a$ axis. As a consequence, the spin-orbit coupling breaks the time-reversal symmetry, and the broken Weyl nodal lines give birth to one pair of Weyl points near the Fermi level. The chiral Weyl nodes, protected by the space inversion and the $C_{3z}$-rotation symmetry, act as the monopole source and sink of the Berry curvature and boost a large anomalous Hall conductivity approaching 580 ${\mathrm{\Omega }}^{-1}{\mathrm{cm}}^{-1}$. This work unveils the magnetic, electronic, and topological properties as well as the anomalous Hall effect of ${\mathrm{Rh}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$, which will facilitate future research on the unexplored topological phenomena in ${\mathrm{Rh}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$.

Rare-earth atoms on top of 2D materials represent an interesting platform with the prospect of tailoring the magnetic anisotropy for practical applications. Here, we investigate the ground state and magnetic properties of selected $4f$ atoms deposited on a graphene substrate in the framework of the $\mathrm{DFT}+U$ approach. The inherent strong spin-orbit interaction in conjunction with crystal field effects acting on the localized $4f$ shells results in a substantial magnetic anisotropy energy (tens of meVs), whose angular dependence is dictated by the $C_{6v}$ symmetry of the graphene substrate. We obtain the crystal-field parameters and investigate spin-flip events via quantum tunneling of magnetization in the view of achieving a protected quantum-spin behavior. Remarkably, the large spin and orbital moments of the open $4f$ shells (Dy, Ho, and Tm) generate a strong magnetoelastic coupling which provides more flexibility to control the magnetic state via the application of external strain.

Magnetic skyrmions are promising for next-generation information storage and processing owing to their potential advantages in data storage density, robustness, and energy efficiency. The magnetic multilayers consisting of Pt, Co, and a third metal element $X$ provide an ideal platform to study skyrmions due to their highly tunable magnetic properties. Here, we report the observation of room-temperature bubblelike Néel skyrmions in epitaxial Pt/Co/Cu multilayers in samples with multidomain states in zero field. The magneto-optic Kerr effect and a superconducting quantum interference device magnetometry are applied to investigate the shapes of the hysteresis loops, the magnetic anisotropy, and the saturation magnetization. By tuning the Co thickness and the number of periods, we achieve perpendicular and in-plane magnetized states and multidomain states that are identified by a wasp-waisted hysteresis loop. Skyrmions are directly imaged by magnetic force microscopy and Lorentz transmission electron microscopy. The development of room-temperature skyrmions in Pt/Co/Cu multilayers may lead to advances in skyrmion-related research and applications.

Phase separation naturally occurs in a variety of magnetic materials and it often has a major impact on both electric and magnetotransport properties. In resistive switching systems, phase separation can be created on demand by inducing local switching, which provides an opportunity to tune the electronic and magnetic state of the device by applying voltage. Here we explore the magnetotransport properties in the ferromagnetic oxide ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ (LSMO) during the electrical triggering of an intrinsic metal-insulator transition (MIT), which produces volatile resistive switching. This switching occurs in a characteristic spatial pattern, i.e., the formation of a high-resistance barrier perpendicular to the current flow, enabling an electrically actuated ferromagnetic-paramagnetic-ferromagnetic phase separation. At the threshold voltage of the MIT triggering, both anisotropic and colossal magnetoresistances exhibit anomalies including a large increase in magnitude and a sign flip. Computational analysis revealed that these anomalies originate from the coupling between the switching-induced phase separation state and the intrinsic magnetoresistance of LSMO. This work demonstrates that driving the MIT material into an out-of-equilibrium resistive switching state provides the means for electrical control of the magnetotransport phenomena.

We present a pair distribution function (PDF) analysis from neutron diffraction data of the ${\mathrm{Ni}}_{1-x}{\mathrm{V}}_x$ alloy in the Ni-rich regime. Such structural study aims to clarify the origin of the magnetic inhomogeneities associated with the quantum Griffiths phase close to the ferromagnetic-paramagnetic quantum phase transition. The PDF analysis successfully reveals information about structural and atomic disorder comparing short-range correlations in our ${\mathrm{Ni}}_{1-x}{\mathrm{V}}_x$ polycrystalline samples prepared with high-temperature annealing and rapid cooling protocol. This study confirms the expectations that all ${\mathrm{Ni}}_{1-x}{\mathrm{V}}_x$ samples with $0\le x\le 0.15$ crystallize in a single phase fcc structure with some residual strain. The lattice constant and the atomic displacement parameter increase with V concentration $x$. Both changes are consistently explained by a random occupation of V and Ni atoms on the lattice sites with small displacements due to the different atomic radii with ratio ($r_{\text{V}}/r_{\text{Ni}}$) of 1.05. Probing alternate, simple models of the local PDF, such as V clusters or ordered structures (${\mathrm{Ni}}_8\mathrm{V}, {\mathrm{Ni}}_3\mathrm{V}$), gives inferior results compared to a random occupation. This investigation strongly supports the magnetic clusters in the binary alloy ${\mathrm{Ni}}_{1-x}{\mathrm{V}}_x$ originating from Ni-rich regions created from random occupation rather than from chemical clusters. The simple tests already demonstrate that ${\mathrm{Ni}}_{1-x}{\mathrm{V}}_x$ is one of the rare examples of a solid solution in a wide concentration regime (up to $x=0.15$) persisting down to low temperatures ($T=15\mathrm{K}$).

Amorphous silica (a-${\mathrm{SiO}}_2$) is a foundational disordered material for which the thermal transport properties are important for various applications. To accurately model the interatomic interactions in classical molecular dynamics (MD) simulations of thermal transport in a-${\mathrm{SiO}}_2$, we herein develop an accurate yet highly efficient machine-learned potential model that allows us to generate a-${\mathrm{SiO}}_2$ samples closely resembling experimentally produced ones. Using the homogeneous nonequilibrium MD method and a proper quantum-statistical correction to the classical MD results, quantitative agreement with experiments is achieved for the thermal conductivities of bulk and 190-nm-thick a-${\mathrm{SiO}}_2$ films over a wide range of temperatures. To interrogate the thermal vibrations at different temperatures, we calculated the current correlation functions corresponding to the transverse acoustic and longitudinal acoustic collective vibrations. The results reveal that, below the Ioffe-Regel crossover frequency, phonons as well-defined excitations remain applicable in a-${\mathrm{SiO}}_2$ and play a predominant role at low temperatures, resulting in a temperature-dependent increase in thermal conductivity. In the high-temperature region, more phonons are excited, accompanied by a more intense liquidlike diffusion event. We attribute the temperature-independent thermal conductivity in the high-temperature range of a-${\mathrm{SiO}}_2$ to the collaborative involvement of excited phonon scattering and liquidlike diffusion in heat conduction. These findings provide physical insights into the thermal transport of a-${\mathrm{SiO}}_2$ and are expected to be applied to a vast range of amorphous materials.

We study one-dimensional hybrid quantum circuits perturbed by quenched quasiperiodic (QP) modulations across the measurement-induced phase transition (MIPT). Considering non-Pisot QP structures, characterized by unbounded fluctuations, allows us to tune the wandering exponent $\beta$ to exceed the Luck bound $\nu \ge 1/(1-\beta )$ for the stability of the MIPT, where $\nu =1.28\left(2\right)$. Via robust numerical simulations of random Clifford circuits interleaved with local projective measurements, we find that sufficiently large QP structural fluctuations destabilize the MIPT and induce a flow to a broad family of critical dynamical phase transitions of the infinite QP type that is governed by the wandering exponent $\beta$. We numerically determine the associated critical properties, including the correlation length exponent consistent with saturating the Luck bound, and a universal activated dynamical scaling with activation exponent $\psi \cong \beta$, finding excellent agreement with the conclusions of real-space renormalization group calculations.

Recently, the inertia has been demonstrated for magnetization dynamics, such as the nutational resonance and spin wave, as well as the inertial switching. Here, we focus on the inertial effect of self-oscillations induced by the spin-orbit torques in easy-axis antiferromagnets. Utilizing the stability analysis of equilibria and the exact solution of precession, we analytically construct the phase diagram controlled by the current and the inertial relaxation time. We then show that the magnetic inertia expands the tunable range of oscillation, the frequency of which is in the terahertz regime. Meanwhile, the frequency is proportional to the current and can enter an ultrahigh regime. Particularly, a lager-amplitude oscillation always persists when increasing the current. These features stand in sharp contrast to the case without an inertia, for which the amplitude of oscillation decreases with an increasing current and the oscillation fades away beyond a critical current. Our results not only enrich the nonlinear magnetic dynamics involving the inertial effect but also provide guidelines for the terahertz application of antiferromagnetic spintronics.