We investigate the interplay of electronic correlations and spin-orbit coupling (SOC) for a one-band and two-band honeycomb lattice models. The main difference between the two models concerning SOC is that in the one-band case the SOC is a purely nonlocal term in the basis of the $p_z$ orbitals, whereas in the two-band case with $p_x$ and $p_y$ as basis functions, it is purely local. In order to grasp the correlation effects on nonlocal spin-orbit coupling, we apply the TRILEX approach that allows to calculate nonlocal contributions to the self-energy approximately. For the two-band case, we apply dynamical mean-field theory. In agreement with previous studies, we find that for all parameter values in our study, the effect of correlations on the spin-orbit coupling strength is that the bare effective SOC parameter is increased. However, this increase is much weaker in the nonlocal than in the local SOC case. Concerning the TRILEX method, we introduce the necessary formulas for calculations with broken SU(2) symmetry.

Full Heusler compounds with cobalt as a primary element show anomalous transport properties owing to the Weyl fermions and broken time-reversal symmetry. We present here the study of anomalous Hall effect (AHE) in the ${\mathrm{Co}}_2\mathrm{FeGe}$ Heusler compound. The experiment reveals anomalous Hall conductivity (AHC) $\sim 100$ S/cm at room temperature with an intrinsic contribution of $\sim 78$ S/cm. The analysis of anomalous Hall resistivity suggests the scattering independent intrinsic mechanism dominates the overall behavior of anomalous Hall resistivity. The first principles calculation reveals that the Berry curvature originated by a gapped nodal line near $E_F$ is the main source of AHE in the ${\mathrm{Co}}_2\mathrm{FeGe}$ Heusler compound. The theoretically calculated AHC is in agreement with the experiment.

Theoretically, the helical edge states of two-dimensional topological insulators are protected from coherent backscattering due to nonmagnetic disorder provided electron interactions are not too strong. Experimentally, the edges typically do not demonstrate systematic and robust quantization, but at the same time little is known about the sub-Kelvin temperature behavior. Here, we report the surprising localization of the edge states in an 8-nm HgTe quantum well in zero magnetic field at millikelvin temperatures. Additionally, the magnetoresistance data at $0.5\mathrm{K}$ for edges a few micrometers long suggest the field-dependent localization length $l_B\propto B^{-\alpha }$, with $\alpha$ ranging approximately from 1.6 to 2.8 at fields $B\lesssim 0.1\text{T}$ and $\alpha \approx 1.1$ at higher fields up to $0.5\text{T}$. In the frame of the disordered interacting edge, these values of $\alpha$ correspond to the Luttinger liquid parameters $K\approx 0.9–1.1$ and $K\approx 0.6$, respectively. We discuss possible scenarios which could result in zero magnetic field localization.

Small form-factor, narrow band, and highly directive antennas are of critical importance in a variety of applications spanning wireless communications, remote sensing, Raman spectroscopy, and single photon emission enhancement. Surprisingly, we show that the classical directivity limit can be appreciably surpassed for electrically small multilayer spherical antennas excited by a point electric dipole even if limiting ourselves to purely dielectric materials. Experimentally feasible designs of superdirective antennas are established by using a stochastic optimization algorithm combined with a rigorous analytic solution.

Among non-Hermitian systems, pseudo-Hermitian phases represent a special class of physical models characterized by real energy spectra and the absence of non-Hermitian skin effects. Here we show that several pseudo-Hermitian phases in two and three dimensions can be built by employing $q$-deformed matrices, which are related to the representation of deformed algebras. Through this algebraic approach, we present and study the pseudo-Hermitian version of well-known Hermitian topological phases, ranging from two-dimensional Chern insulators and time-reversal-invariant topological insulators to three-dimensional Weyl semimetals and chiral topological insulators. We analyze their topological bulk states through non-Hermitian generalizations of Abelian and non-Abelian tensor Berry connections and quantum metrics. Although our pseudo-Hermitian models and their Hermitian counterparts share the same topological invariants, their band geometries are different. We indeed show that some of our pseudo-Hermitian phases naturally support nearly flat topological bands, opening the route to the study of pseudo-Hermitian strongly interacting systems. Finally, we provide an experimental protocol to realize our models and measure the full non-Hermitian quantum geometric tensor in synthetic matter.

Recent experimental and theoretical investigations demonstrate that twisted trilayer graphene (tTLG) is a highly tunable platform to study the correlated insulating states, ferromagnetism, and superconducting properties. Here we explore the possibility of tuning electronic correlations of the tTLG via a vertical pressure. A full tight-binding model is used to accurately describe the pressure-dependent interlayer interactions. Our results show that pressure can push a relatively larger twist angle (for instance, $1.{89}^{\circ }$) tTLG to reach the flat-band regime. Next, we obtain the relationship between the pressure-induced magic angle value and the critical pressure. These critical pressure values are almost half of that needed in the case of twisted bilayer graphene. Then, plasmonic properties are further investigated in the flat-band tTLG with both zero-pressure magic angle and pressure-induced magic angle. Two plasmonic modes are detected in these two kinds of flat-band samples. By comparison, one is a high energy damping-free plasmon mode that shows similar behavior, and the other is a low energy plasmon mode (flat-band plasmon) that shows obvious differences. The flat-band plasmon is contributed by both interband and intraband transitions of flat bands, and its divergence is due to the various shape of the flat bands in tTLG with zero-pressure and pressure-induced magic angles. This may provide an efficient way of tuning between regimes with strong and weak electronic interactions in one sample and overcoming the technical requirement of precise control of the twist angle in the study of correlated physics.

Topological insulator (TI) thin films with surface magnetism are expected to exhibit a quantized anomalous Hall effect (QAHE) when the magnetizations on the top and bottom surfaces are parallel, and a quantized topological magnetoelectric effect (QTME) when the magnetizations have opposing orientations (axion-insulator phase) and the films are sufficiently thick. We present a unified picture of both effects that associates deviations from exact quantization of the QTME caused by finite thickness with nonlocality in the sidewall current response function. Using realistic tight-binding model calculations, we show that in ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ TI thin films, deviations from quantization in the axion-insulator phase are reduced in size when the exchange coupling of tight-binding model basis states to the local magnetization near the surface is strengthened. Stronger exchange coupling also reduces the effect of potential disorder, which is unimportant for the QAHE but detrimental for the QTME, which requires that the Fermi energy lie inside the gap at all positions.

Electronic topology in metallic kagome compounds is under intense scrutiny. We present transport experiments in ${\mathrm{Na}}_{2/3}\mathrm{Co}{\mathrm{O}}_2$ in which the Na order differentiates a Co kagome sublattice in the triangular $\mathrm{Co}{\mathrm{O}}_2$ layers. Hall and magnetoresistance (MR) data under high fields give evidence for the coexistence of light and heavy carriers. At low temperatures, the dominant light carrier conductivity at zero field is suppressed by a $B$-linear MR, suggesting Dirac-like quasiparticles. Lifshitz transitions induced at large $B$ and $T$ unveil the lower mobility carriers. They display a negative $B^2$ MR due to scattering from magnetic moments likely pertaining to a flat band. We emphasize an analogy with heavy fermion physics.

Local phonon properties near heterointerfaces or lattice defects are key for controlling various material properties such as thermal conductivity and thermoelectricity. However, high-spatial-resolution measurements of bulk phonons have hardly been established, even in typical nonpolar and polar bulk materials such as diamond and cubic boron nitride (c-BN), respectively. Here, we demonstrate nanometric measurements of phonon dispersions and mapping using a heterojunction of diamond and c-BN single crystals. To achieve high spatial/energy resolution, we use a monochromated (∼20–30 meV) electron nanoprobe, a high-sensitivity scintillator for counting inelastically scattered electrons, and the Richardson–Lucy deconvolution. The diamond phonon dispersion is first measured under a large-scattering-vector condition, particularly for the Γ point. Differential scattering cross sections of optical and acoustic-phonon modes in diamond and c-BN are also measured, and the totals of their modes are on the order of ${10}^{-5}\mathrm{n}{\mathrm{m}}^2$ for both crystals.

Here, a phase diagram with phase coexistence near the polycrystalline phase boundary has been studied on $\left(1\text{−}x\right){\mathrm{AgNbO}}_3\text{−}x{\mathrm{LiTaO}}_3$ ceramics by analyzing infrared- (IR) and Raman-active phonon dynamics under tuning chemical component and temperature. Optical dielectric functions, ferroelectric domain, and electronic transitions promote the understanding of lattice structure in ${\mathrm{AgNbO}}_3$, and the antiferroelectric (AFE) to ferroelectric (FE) transformation, which results from the joint effect of the cationic antipolar and the oxygen octahedron distortion. The spectroscopic methods of x-ray diffraction, IR reflection, and Raman scattering reveal the mixed phase boundary at $x$ (${\mathrm{LiTaO}}_3$) = 0.05, which is the indication of a first-order transition, contributing to the excellent pyroelectric property. Note that the soft mode near 50 ${\mathrm{cm}}^{-1}$ is sensitive to reveal the lattice transformation. Moreover, the temperature-dependent optical band gap ( $E_g$ ) with the specific electronic transition behavior has been further explored, and becomes complementary evidence for the structural phase transition. This study presents the systematical results on structural properties and optical/dielectric properties for the state-of-the-art ${\mathrm{AgNbO}}_3$ system for designing energy-storage devices.

We propose a mechanism for opening a full bulk energy gap and inducing vortex Majorana zero modes (MZMs) in nodal superconductors (SCs). We show that this becomes possible by coupling the nodal SC of interest to a magnetic texture crystal. The latter consists of superpositions of magnetic textures which repeat periodically in space according to suitable wave vectors that enable spin-flip scattering between all pairs of nodes of the SC, and thus open a full gap in its bulk energy spectrum. In this event, MZMs can be trapped in spin or shift vortices introduced in the magnetic texture crystal. Our approach is generic and applies to nodal SCs of spin-singlet, -triplet, or -mixed type of pairing. Therefore it promises to find application in a variety of nodal SCs, where the magnetic textures appear either spontaneously due to electron-electron interactions or are imposed by nanomagnets or become induced by coupling to a lattice of localized magnetic moments.

Thermal conductivity ($\kappa$) of mantle minerals is key to understanding dynamics in the deep Earth. It controls the style of mantle convection and the timescale of cooling both the mantle and the core. Cubic ${\mathrm{CaSiO}}_3$ perovskite (CaPv) is the third most abundant mineral in the lower mantle ($7\mathrm{vol}\%$). Despite its importance, no theoretical or experimental estimate of CaPv's $\kappa$ is available. Theoretical investigations of its properties are challenging because of its strong anharmonicity. Experimental measurements at relevant pressures and temperatures are equally challenging. Here we present ab initio results for CaPv's $\kappa$ obtained using the phonon quasiparticle approach to address its strong anharmonicity. We also offer experimental measurements of $\kappa$ up to 67 GPa and 1950 K. Predictions and measurements are in good agreement and reveal a surprisingly large $\kappa$ for cubic CaPv that can be explained on the basis of its high crystal structure symmetry. Despite its relatively low abundance, CaPv's $\kappa$ increases the lower mantle $\kappa$ by $\sim 10\%$, if accounted for. $\kappa$ of mantle regions enriched in subducted crustal materials will be more strongly impacted.

We report on a solution-growth based method to synthesise single crystals of ${\mathrm{Y}}_2{\mathrm{Co}}_3$ and on its structural and magnetic properties. We find that ${\mathrm{Y}}_2{\mathrm{Co}}_3$ crystallizes in the ${\mathrm{La}}_2{\mathrm{Ni}}_3$-type orthorhombic structure with space group $Cmce$ (No. 64), with Co forming distorted kagome lattices. ${\mathrm{Y}}_2{\mathrm{Co}}_3$ orders antiferromagnetically below $T_{\text{N}}=252$ K. Magnetization measurements reveal that the moments are primarily aligned along the $b$ axis with evidence for some canting. Band-structure calculations indicate that ferromagnetic and antiferromagnetic orders are nearly degenerate, at odds with experimental results. Magnetization measurements under pressure up to 1 GPa reveal that the Néel temperature decreases with the slope of $-1.69$ K/GPa. We observe a field-induced spin-flop transition in the magnetization measurements at 1.5 K and 21 T with magnetic field along the $b$ direction. The magnetization is not saturated up to 35 T, indicating that the antiferromagnetic ordering in ${\mathrm{Y}}_2{\mathrm{Co}}_3$ is quite robust, which is surprising for such a Co-rich intermetallic.

We show that the quantum geometry of the Fermi surface can be numerically described by a three-dimensional discrete quantum manifold. This approach not only avoids singularities in the Fermi sea, but it also enables the precise computation of the intrinsic Hall conductivity resolved in spin, as well as any other local properties of the Fermi surface. The method assures numerical accuracy when the Fermi level is arbitrarily close to singularities, and it remains robust when Kramers degeneracy is protected by symmetry. The approach is demonstrated by calculating the anomalous Hall and spin Hall conductivities of a two-band lattice model of a Weyl semimetal and a full-band ab initio model of zinc-blende GaAs.

At ambient pressure, studies of resistivity, magnetic susceptibility, and carbon-13 nuclear magnetic resonance (NMR) were conducted on the quasi-one-dimensional organic conductor ${\left(\text{DMET-}\mathrm{TTF}\right)}_2{\mathrm{AuBr}}_2$. Resistivity measurements showed a broad minimum at approximately 160 K, and the insulator behavior below this temperature and magnetic susceptibility results revealed a dip structure at 22 K. At the same temperature, a sharp peak in the temperature dependence of $T_1^{-1}$ associated with the antiferromagnetic (AFM). transition was found, along with drastic splitting of the NMR spectra, indicating a commensurate AFM structure. The amplitude of the magnetic moments was determined to be $0.06{\mu }_B$/molecule from the hyperfine coupling constant tensor and the angular dependence of the internal field in the AFM phase. The small magnetic moment signifies the AFM nesting type, i.e., commensurate spin density wave. An antiferromagnetic ordering of $(\uparrow \uparrow \downarrow \downarrow )$ along the one-dimensional chain is expected from the $2k_{\mathrm{F}}$ instability. This behavior can be explained by the strong dimerization of the one-dimensional DMET-TTF chain.

It is recently found that the Hall effect can survive in the presence of time-reversal symmetry but with inversion-symmetry breaking, which is known as the nonlinear Hall effect. So far, the studies concerning the nonlinear Hall effect are mainly focused on the homogeneous systems, while less attention has been paid to the van der Waals (vdW) heterostructure, which in fact naturally breaks the spatial inversion symmetry. In this study, we systematically study the nonlinear electric response in $1{\text{T}}^{\prime }$-phase ${\mathrm{MoSe}}_2/{\mathrm{WSe}}_2$ vdW heterostructure. Our results demonstrate that ${\mathrm{MoSe}}_2/{\mathrm{WSe}}_2$ vdW heterostructure owns a large Berry curvature dipole, which is comparable with those of homogeneous multilayers and much larger than that predicted for monolayers under the in-plane uniaxial strain. In addition, the nonlinear Hall response in vdW heterostructure is sensitive to the relative position between the Fermi energy and tilted Dirac cones, and can be effectively manipulated from positive to negative values by applying an out-of-plane strain. Further study indicates that this can be ascribed to the charge transfer within the vdW interlayer. Based on these findings, our work provides a fundamental understanding of the nature of strain-gated nonlinear Hall effect in vdW heterostructures, which may facilitate the design of novel high-frequency nanodevices.

Using the combined density functional and dynamical mean-field theory, we study relativistic corrections to the Fermi surface of palladium. We find, indeed, that relativistic corrections create small hole pockets at the $L$-symmetry points. Furthermore, we show that the computed two-dimensional angular correlation of electron positron annihilation radiation (2D-ACAR) clearly demonstrates the existence of these $L$-hole pockets, which remains robust against electronic correlations. A 2D-ACAR experiment should therefore provide the smoking-gun proof of the existence of $L$-hole pockets in the palladium Fermi surface.

Quantum thermodynamics is a promising route to unambiguous detections of Majorana bound states. Being fundamentally different from quantum transport, this approach reveals unique Majorana thermodynamic behavior and deepens our insight into Majorana quantum transport itself. Here, we demonstrate that a nanoscopic system with topological superconductors produces a remarkable accumulation of Majorana thermodynamic states in wide ranges of Majorana tunneling phases by means of increasing its temperature $T$. Revealing this physical behavior is twofold beneficial. First, it significantly reduces the dependence of the entropy on the tunneling phases which become almost irrelevant in experiments. Second, the fractional Majorana entropy $S_M^{\left(2\right)}=k_{B}ln\left(2^{\frac{3}{2}}\right)$ may be observed at high temperatures, substantially facilitating experiments. Analyzing quantum transport, we predict that when the temperature increases, the above thermodynamic behavior will induce an anomalous increase of the linear conductance from vanishing values up to the unitary fractional Majorana plateau $G_M=e^2/2h$ extending to high temperatures.