Electron-electron interaction (EEI), a quantum effect that occurs in low-dimensional or disordered systems at low temperatures, is an important issue in electron transport phenomena, especially in the anomalous Hall effect (AHE). Nevertheless, the role of EEI correction to the AHE is overlooked in conventional magnetic metal systems and the scaling exponents of the power-law fits are not consistently at the systems with sufficiently high disorder. Here, we demonstrate that EEI does correct to the AHE and cause $\text{ln}T$-type temperature dependence of sheet resistance $R_{xx}$ (conductance $G_{xx}$), anomalous Hall resistance $R_{\mathrm{AH}}$, and anomalous Hall conductance $G_{\mathrm{AH}}$ in ultrathin high-quality FeCo films in the low-temperature region. Furthermore, the scaling exponent γ ∼ 1 is acquired through the power-law fits of $G_{\mathrm{AH}}\sim G_{xx}^{\gamma }$ by varying temperature or thickness, suggesting that EEI corrects to skew scattering and definitely results in skew scattering dominating AHE in the bad metal regime (${\sigma }_{xx}<1\times {10}^4$ S/cm).

Orbitronics is an emerging and fascinating field that explores the utilization of the orbital degree of freedom of electrons for information processing. An increasing number of orbital phenomena are being currently discovered, with spin-orbit coupling mediating the interplay between orbital and spin effects, thus providing a wealth of control mechanisms and device applications. In this context, the orbital analog of the spin Dzyaloshinskii-Moriya interaction (DMI), i.e., orbital DMI, deserves to be explored in depth since it is believed to be capable of inducing chiral orbital structures. Here, we unveil the main features and microscopic mechanisms of the orbital DMI in a two-dimensional square lattice using a tight-binding model of $t_{2g}$ orbitals in combination with the Berry phase theory. This approach allows us to investigate and transparently disentangle the role of inversion symmetry breaking, strength of orbital-exchange interaction, and spin-orbit coupling in shaping the properties of the orbital DMI. By scrutinizing the band-resolved contributions, we are able to understand the microscopic mechanisms and guiding principles behind the orbital DMI and its anisotropy in two-dimensional magnetic materials, and uncover a fundamental relation between the orbital DMI and its spin counterpart, which is currently being explored very intensively. The insights gained from our work contribute to advancing our knowledge of orbital-related effects and their potential applications in spintronics, providing a path for future research in the field of chiral orbitronics.

We study the role of the inter- and intraband current in the laser interaction with the bichromatic quasiperiodic crystals. The interaction dynamics are simulated by solving the time-dependent Schrödinger equation in the $k$ space, and time evolution of the inter- and intraband current is obtained in a gauge-invariant form. We observed that for certain bichromatic potential ratios, the energy band structure of the “valence band” and the “conduction band” facilitates the interband transitions only at the center or at the edge of the Brillouin zone, which leads to a very interesting population transfer mechanism between the bands. The temporal profile of the inter- and intraband current gives a detailed account of the interaction. The higher-order harmonic generation is also studied for these bichromatic optical lattices, and the resultant harmonic yield is commented upon.

The realization of the single-pair fermions in electronic systems remains challenging in topology physics, especially for the systems with larger chiral charges $C$. In this work, based on the symmetry analysis, low-energy effective models, and first-principles calculations, we identify the single-pair charge-two chiral fermions in cubic lattices. We first derive the minimal lattice model that exhibits a single pair of Weyl points with the opposite chiral charges of $C=\pm 2$. Furthermore, we show the ultralight chiral crystal ${\mathrm{P}4}_{3}32$-type ${\mathrm{LiC}}_2$ and its mirror enantiomer as high-quality candidate materials, which exhibit large energy windows to surmount the interruption of irrelevant bands. Since two enantiomers are connected by the mirror symmetry, we observe the opposite chiral charges $C$ and the reversal of Fermi-arc connections, showing the correspondence of chirality in the momentum space and the real space. In addition, we also reveal type-II van Hove singularities on the helicoid surfaces, which may induce chirality-locked charge density waves on the crystal surface. Our work not only provides a promising platform for controlling the sign of chiral charge through structural chirality but also facilitates the exploration of electronic correlations on the surface of ultralight chiral crystals.

I point out that Gross-Neveu theory with SO(3) isospin in three space-time dimensions—proposed recently, for instance, as an effective description of the Néel transition in certain spin-orbital liquids—also hosts quantum criticality of a more exotic kind. The ordered phase breaks SO(3) spontaneously, but the SO(3)-Néel order parameter vanishes. The fermionic bilinear order parameter is instead a biadjoint with respect to SO(3); unlike its Néel cousin, it constitutes an interaction-induced insulator. Furthermore, I show that the Néel and biadjoint order parameters can be combined to transform as an adjoint under SU(3) symmetry; the symmetry is emergent at the critical point separating the symmetric semimetal and the biadjoint insulator, but only if the flavor number is small enough, suggesting order-parameter fluctuations and the interplay between different channels play a crucial role in stabilizing the enlarged symmetry. In candidate SO(3) spin-orbital liqiuds, thermodynamic critical exponents carry fingerprints of “spinons.” The existence of an independent universality class in addition to the Néel transition opens the possibility of posing further constraints on spinon properties from thermodynamic measurements near criticality alone.

We present several approximate calculations of the specific heat capacity of the model for ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_7{\mathrm{O}}_{28}$ proposed by Balz et al. [Phys. Rev. B 95, 174414 (2017)], using methods including exact diagonalization, thermal pure quantum states, and high-temperature expansions. In none of these cases are we able to reproduce the magnitude of the zero-field specific heat capacity shown in the intermediate-temperature $(\sim 5–15\mathrm{K})$ experimental data. We discuss possible reasons for the discrepancy, and what it might tell us about the magnetic Hamiltonian for ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_7{\mathrm{O}}_{28}$.

High temperature superconductivity was recently found in the bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ (La327), followed by the discovery of superconductivity in the trilayer ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ (La4310), under high pressure. Through studying the electronic correlation of La4310 with $\mathrm{DFT}+\mathrm{DMFT}$, and further comparing it with that of La327, we find that the $e_g$ orbitals of the outer-layer Ni cations in La4310 have a similar (but slightly weaker) electronic correlation to those in La327, in which the electrons behave as a non-Fermi liquid with Hund correlation and linear-in-temperature scattering rate. Our results suggest that the experimentally observed “strange metal” behavior may be explained by the Hund spin correlation featuring high spin states and spin-orbital separation. In contrast, the electrons in the inner-layer Ni cations in La4310 behave as a Fermi liquid. The weaker electronic correlation in La4310 is attributed to more hole doping, which may explain its lower superconducting transition temperature.

We studied single and two Su-Schrieffer-Heeger wires on a simple cubic semiconducting substrate. The wire-wire coupling is either perpendicular or diagonal hopping respecting the particle-hole and time-reversal symmetries. The hybridization to the substrate renormalizes the model parameters of the wires toward the hopping parameter of the substrate without changing the basic nature of perpendicular or diagonal coupling and it can mediate effective perpendicular hopping but not diagonal hopping in the absence of direct wire-wire coupling. This justifies the investigation of multi-uniform tight-binding wires with perpendicular or diagonal hopping parameters while neglecting the substrate. Perpendicularly coupled uniform wires reveal an anisotropic two-dimensional band dispersion. Diagonally coupled uniform wires reveal strictly one-dimensional bands parallel to the wires direction if the intrawire hopping parameter is larger than twice the diagonal hopping parameter despite strong dispersion perpendicular to the wires. Otherwise, they reveal strictly one-dimensional bands parallel and perpendicular to the wires direction simultaneously. We established the possibility of realizing strictly one-dimensional properties emerging from dispersive two-dimensional systems if time-reversal and particle-hole symmetries are respected. This can facilitate the investigations of Luttinger liquid in the Au/Ge(001) and Bi/InSb(001) surface reconstructions.

Strong interactions present in single-layer RbI grown on metal surfaces have been shown to result in the surprising coexistence of bistable RbI structures. However, it is not well known how these structural differences affect the electronic behavior of the RbI film. Here, we use scanning tunneling microscopy/spectroscopy (STM/STS) to probe the image potential electronic states (IPSs) of the RbI/Ag(111) system, which are known to be highly sensitive to the electronic properties of ultrathin insulating films. By comparing our experimental STS measurements to first-principles numerical simulations of the IPSs, we calculate the work function, dielectric constant, and conduction band energy for the two distinct structure types of RbI on Ag(111). In addition, our results show that local variations in the IPS behavior, evident in both a moiré pattern and grain boundary defects, can be attributed to electrostatic potentials present in the RbI structure.

We investigate the electronic structure and the optical absorption onset of close-to-${30}^{\circ }$ twisted hexagonal boron nitride bilayers. Our study is carried out with a purposely developed tight-binding model validated against density functional theory simulations. We demonstrate that approaching ${30}^{\circ }$ (quasicrystal limit), all bilayers sharing the same moiré supercell develop identical band structures, irrespective of their stacking sequence. This band structure features a bundle of flat bands lying slightly above the bottom conduction state which is responsible for an intense peak at the onset of the absorption spectrum. These results suggest the presence of strong, stable and stacking-independent excitons in boron nitride ${30}^{\circ }$-twisted bilayers. By carefully analyzing the electronic structure and its spatial distribution, we elucidate the origin of these states as moiré-induced $K$-valley scattering due to interlayer $\mathrm{B}\text{−}\mathrm{B}$ coupling. We take advantage of the physical transparency of the tight-binding parameters to derive a simple triangular model based on the B sublattice that accurately describes the emergence of the bundle. As our conclusions very general, we predict that a similar bundle should emerge in other close-to-${30}^{\circ }$ bilayers, such as transition metal dichalcogenides, shedding light on the unique potential of two-dimensional materials.

A $d$-dimensional elastic manifold at depinning is described by a renormalized field theory, based on the functional renormalization group (FRG). Here, we analyze this theory to 3-loop order, equivalent to third order in $\epsilon =4-d$, where $d$ is the internal dimension. The critical exponent reads $\zeta =\frac{\epsilon }{3}+0.04777{\epsilon }^2-0.068354{\epsilon }^3+O\left({\epsilon }^4\right)$. Using that $\zeta (d=0)=2^{-}$, we estimate $\zeta (d=1)=1.266\left(20\right)$, $\zeta (d=2)=0.752\left(1\right)$, and $\zeta (d=3)=0.357\left(1\right)$. For Gaussian disorder, the pinning force per site is estimated as $f_{\mathrm{c}}=\mathcal{B}{m}^2{\rho }_m+f_{\mathrm{c}}^0$, where $m^2$ is the strength of the confining potential, $\mathcal{B}$ a universal amplitude, ${\rho }_m$ the correlation length of the disorder, and $f_{\mathrm{c}}^0$ a nonuniversal lattice-dependent term. For charge-density waves, we find a mapping to the standard ${\varphi }^4$ theory with $O\left(n\right)$ symmetry in the limit of $n\to -2$. This gives $f_{\mathrm{c}}=\tilde{\mathcal{A}}\left(d\right)m^{2}ln\left(m\right)+f_{\mathrm{c}}^0$, with $\tilde{\mathcal{A}}\left(d\right)=-{\partial }_n{[\nu {(d,n)}^{-1}+\eta (d,n)]}_{n=-2}$, reminiscent of logarithmic conformal field theories.

The effect of carrier localization due to electron-electron interaction in the anomalous Hall effect is elusive and there are contradictory results in the literature. To address the issue, we report here the detailed transport study including the Hall measurements on $\beta$-Mn type cubic compound ${\mathrm{Co}}_7{\mathrm{Zn}}_7{\mathrm{Mn}}_6$ with a chiral crystal structure, which lacks global mirror symmetry. The alloy orders magnetically below $T_c$ = 204 K, and is reported to show spin glass state at low temperature. The longitudinal resistivity (${\rho }_{xx}$) shows a pronounced upturn below $T_{\text{min}}$ = 75 K, which is found to be associated with carrier localization due to quantum interference effect. The upturn in ${\rho }_{xx}$ shows a $T^{1/2}$ dependence and it is practically insensitive to the externally applied magnetic field, which indicates that electron-electron interaction is primarily responsible for the low-$T$ upturn. The studied sample shows a considerable value of the anomalous Hall effect below $T_c$. We found that the localization effect is present in the ordinary Hall coefficient ($R_0$), but we failed to observe any signature of localization in the anomalous Hall resistivity or conductivity. The absence of localization effect in the anomalous Hall effect in ${\mathrm{Co}}_7{\mathrm{Zn}}_7{\mathrm{Mn}}_6$ may be due to large carrier density, and it warrants further theoretical investigations, particularly with systems having broken mirror symmetry.

A novel class of antiferromagnets, dubbed altermagnets, exhibit a nonrelativistically spin-split band structure reminiscent of the order parameter phase $d$-wave superconductors, despite the absence of net magnetization. This unique characteristic enables utilization in cryogenic stray-field-free memory devices, offering the possibility of achieving high storage densities. We here determine how a proximate altermagnet influences the critical temperature $T_c$ of a conventional $s$-wave singlet superconductor. Considering both a bilayer and trilayer, we show that such hybrid structures may serve as stray-field-free memory devices where the critical temperature is controlled by rotating the Néel vector of one altermagnet, providing infinite magnetoresistance. Furthermore, our study reveals that altermagnetism can coexist with superconductivity up to a critical strength of the altermagnetic order as well as robustness of the altermagnetic influence on the conduction electrons against nonmagnetic impurities, ensuring the persistence of the proximity effect under realistic experimental conditions.

Understanding out-of-equilibrium many-body quantum systems is an essential task in contemporary physics. While advanced numerical methods have been developed, capturing the universal dynamics of generic many-body quantum systems still remains a significant challenge. In this study, we focus on the multichannel Kondo impurity (MCKI) model, an intriguing theoretical model hosting an overscreened Kondo state with non-Fermi-liquid characteristics, which serves as a theoretical platform for investigating universal properties in many-body quantum dynamics. Utilizing the large-$N$ Schwinger-Keldysh approach, we systematically investigate both transient dynamics and long-time quasiequilibrium properties in the MCKI model following a sudden change of the Kondo coupling. Our investigations encompass two distinct initial states: the overscreened Kondo state and the high-temperature Fermi-liquid state. For the overscreened Kondo state initial condition, we observe oscillations in various physical observables, including spin-spin correlations and the Kondo order parameter. These oscillations signify the quantum revival of the entangled state that characterizes the overscreened Kondo state. On the other hand, in the case of the high-temperature Fermi-liquid initial state, the absence of oscillations can be attributed to the dephasing mechanism. Furthermore, we discover that the system reaches a quasiequilibrium on an $O\left(1\right)$ timescale. This quasiequilibrium manifests as incoherent thermalization between the impurity and the conduction electrons, in which we observe the nonvanishing effective temperature difference between the Abrikosov fermion representing the impurity spin and the composite boson formed by the Abrikosov fermion and the conduction electrons at the impurity site. This quasiequilibrium can be interpreted as prethermalization. Incorporating the $1/N$ correction, we demonstrate that the system attains complete thermalization on an $O\left(N\right)$ timescale. Additionally, we discuss the quantum cooling effect and quantum Boltzmann equations. Our comprehensive study establishes a foundation for investigating quantum many-body systems using large-$N$ quantum field-theory treatment, while our findings reveal several universal properties of quantum dynamics and provide a different perspective on prethermalization.

We study the statistical mechanics and the equilibrium dynamics of a system of classical Heisenberg spins with frustrated interactions on a $d$-dimensional simple hypercubic lattice, in the limit of infinite dimensionality $d\to \infty$. In the analysis we consider a class of models in which the matrix of exchange constants is a linear combination of powers of the adjacency matrix. This choice leads to a special property: the Fourier transform of the exchange coupling $J\left(\mathbf{k}\right)$ presents a $(d-1)$-dimensional surface of degenerate maxima in momentum space. Using the cavity method, we find that the statistical mechanics of the system presents for $d\to \infty$ a paramagnetic solution which remains locally stable at all temperatures down to $T=0$. To investigate whether the system undergoes a glass transition we study its dynamical properties assuming a purely dissipative Langevin equation, and mapping the system to an effective single-spin problem subject to a colored Gaussian noise. The conditions under which a glass transition occurs are discussed including the possibility of a local anisotropy and a simple type of anisotropic exchange. The general results are applied explicitly to a simple model, equivalent to the isotropic Heisenberg antiferromagnet on the $d$-dimensional face-centered-cubic lattice with first- and second-nearest-neighbor interactions tuned to the point $J_1=2J_2$. In this model, we find a dynamical glass transition at a temperature $T_{\mathrm{g}}$ separating a high-temperature liquid phase and a low-temperature vitrified phase. At the dynamical transition, the Edwards-Anderson order parameter presents a jump demonstrating a first-order phase transition.

In this work, we study magnetoelastic interactions by means of ultrasound experiments in $\alpha \text{−}{\mathrm{RuCl}}_3$—a prototypical material for the Kitaev spin model on the honeycomb lattice, with a possible spin-liquid state featuring Majorana fermions and ${\mathbb{Z}}_2$-flux excitations. We present results of the temperature and in-plane magnetic-field dependence of the sound velocity and sound attenuation for several longitudinal and transverse phonon modes propagating along high-symmetry crystallographic directions. A comprehensive data analysis above the magnetically ordered state provides strong evidence of phonon scattering by Majorana fermions. This scattering depends sensitively on the value of the phonon velocities relative to the characteristic velocity of the low-energy fermionic excitations describing the spin dynamics of the underlying Kitaev magnet. Moreover, our data displays a distinct reduction of anisotropy of the sound attenuation, consistent with the presence of thermally excited ${\mathbb{Z}}_2$ visons. We demonstrate the potential of phonon dynamics as a promising probe for uncovering fractionalized excitations in $\alpha \text{−}{\mathrm{RuCl}}_3$ and provide new insights into the $H\text{−}T$ phase diagram of this material.

Wannier functions have widespread utility in condensed matter physics and beyond. Topological physics, on the other hand, has largely involved the related notion of compactly supported Wannier-type functions, which arise naturally in flat bands. In this paper, we establish a connection between these two notions, by finding the necessary and sufficient conditions under which compact Wannier functions exist in one dimension. We present an exhaustive construction of models with compact Wannier functions and show that the Wannier functions are unique, and in general, distinct from the corresponding maximally localized Wannier functions.

Weyl-semimetal superstructures with a spiraling position of a pair of Weyl nodes of opposite chirality can host a chiral-symmetry-preserving Fermi-arc metal state, where the chirality is carried by cylindrical Fermi surfaces, electronlike and holelike depending on the chirality. The Fermi surfaces nest at vanishing momentum separation (zero nesting vector) at the electron-hole-compensation energy because the nesting is topologically protected by vanishing spatial overlap of any pair of equal-momentum opposite-chirality states. In this work we show that the nesting and Coulomb interaction drive a spontaneous chiral symmetry breaking in such a Fermi-arc metal, which leads to a dynamical axion insulator state but without breaking translational symmetry (no charge-density-wave order) as in a conventional Weyl semimetal. As for material realization, we discuss magnetically doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, for which the Weyl-node positions depend on the order of the magnetic dopands. In this case, the axionic condensation can itself stabilize a spiral order of the magnetization, and hence the spiraling node positions, even if the magnetic interaction is intrinsically ferromagnetic.

We have investigated the magnetic, thermodynamic, and electrical transport properties of EuAuSb single crystals as well as carrying out band structure calculations. The powder x-ray diffraction data confirm that EuAuSb crystallizes in ZrBeSi-type hexagonal structure with space group $P{6}_3/mmc$. The magnetic measurements reveal an antiferromagnetic (AFM) ordering in EuAuSb at ${\mathit{T}}_N=3.3$ K. This transition is further confirmed by heat capacity and electrical resistivity data. The isothermal magnetization data saturate at low magnetic field of ${\mu }_0{H}_s^c=2.9$ and ${\mu }_0{H}_s^{ab}=3.8$ T for $\mathit{H}\perp \mathit{c}$ and $\mathit{H}\parallel \mathit{c}$, respectively, while the magnetization along $\mathit{H}\perp \mathit{c}$ displays a metamagnetic transition around ${\mu }_0{H}_m^{ab}=0.95$ T. The electrical resistivity exhibits a metallic behavior down to 35 K; after that it shows an upturn until $T_N$ due to the influence of short-range interactions. The longitudinal and transverse magnetoresistances of EuAuSb are negative ($\sim -45\%$ and $-42\%$ in 10 T at 2 K, respectively); in the high field at $\mathit{T}\le 40$ K, they switch to a positive value above 40 K. Further, we observe a humplike anomaly in the Hall resistivity [${\rho }_{xy}\left(\mathit{H}\right)$] data below $T_N$, which is most likely a manifestation of the topological Hall effect. Our two-band model analysis of ${\rho }_{xy}\left(\mathit{H}\right)$ data indicates both hole and electron charge carriers contribute to the electrical transport of the compound. The electronic band structure calculations reveal a $\mathrm{\Gamma }$-centered nodal line in the absence of spin-orbit coupling (SOC). In the presence of SOC, the compound hosts the Dirac point. The $Z_2$ invariants, in the presence of effective time-reversal and inversion symmetries, categorize this system as a nontrivial topological material. Our combined experimental and theoretical studies suggest EuAuSb to be a potential AFM topological semimetal.