The nonlinear Hall effect arises in materials without inversion symmetry, and the intrinsic contribution is typically from the Berry curvature dipole of nonuniversal Fermi pockets. Here we propose that the nonlinear Hall effect can reach quantization in chiral Weyl semimetals without mirror symmetries. The energy shift between a pair of Weyl nodes leads to chirally asymmetric intranode relaxation, and the net trace of nonlinear Hall conductivity is thus quantized in units of $e^3/{\hslash }^2$ and determined by the sum of monopole charge weighted by the transport relaxation time. Our theory also applies to mirror symmetric Weyl and Dirac semimetals with chiral anomalies. Additionally, besides dc transport probes, we anticipate that nonlinear circular dichroism measurements can detect chiral asymmetry-induced currents.

We theoretically investigate a tunable non-Hermitian skin effect in systems with gain and loss and find that the bipolar (quadripolar) non-Hermitian skin effect is characterized by topological invariants in one (two)-dimensional systems. We also find the partial non-Hermitian skin effect with the coexistence of localized states and extended states. Both types of the non-Hermitian skin effect have not yet been predicted together in a single system. In addition, we propose a feasible experimental scheme for our model that is realizable in electric circuits. Our investigation unveils another type of non-Hermitian skin effect and enhances the tunability of the non-Hermitian systems by gain and loss other than the conventional nonreciprocal hopping.

We employ a density-functional theory plus dynamical mean-field theory framework to investigate the correlated electronic structure of the alternating single-layer–trilayer (1313) polymorph of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, which becomes superconducting under pressure. At ambient pressure, the single layer is in a Mott-insulating regime and the low-energy physics is dominated by the trilayer block. Under pressure, the gap in the single-layer block closes due to orbital-selective physics, enabling charge transfer into the trilayer block. This change in effective doping of the trilayer block could be linked to the higher $T_c$ obtained in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7\text{−}1313$ ($\sim 80$ K) when compared to the nominal trilayer ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ compound ($\sim 30$ K). We conclude that correlation-driven layer differentiation is crucial in the ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7\text{−}1313$ polymorph and that its low-energy physics aligns closely with the trilayer ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ compound (in spite of the apparent differences in nominal filling) rather than with the conventional bilayer ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$.

In various material systems, an antiferromagnetic phase was found to coexist with a weak ferromagneticlike signal, while symmetry-based theoretical predictions indicate a possibility of a nonzero anomalous Hall effect (AHE) even in the absence of sample magnetization. This is the case of nominally collinear antiferromagnets, in particular, hexagonal MnTe, where the AHE and no detectable magnetization have been recently reported. To clarify the role of magnetization, we present a study of bulk MnTe samples, combining experiment and theory. We demonstrate that the existence of the AHE in the hexagonal MnTe is accompanied by the presence of a weak but detectable ferromagneticlike signal, vanishing at the Néel temperature. In contrast to thin layer samples, we find that the AHE hysteresis loop shows an opposite sign and Barkhausen-like jumps. We introduce a macrospin model involving the Dzyaloshinskii–Moriya type interaction, which explains the existence of a nonzero magnetic moment in the absence of external field and reproduces well hysteretic behavior of the AHE. Using analysis of Néel-vector-dependent Berry curvature, we show that the intrinsic AHE in hexagonal MnTe can be nonzero even when the magnetization vanishes and, also, that it changes sign depending on the Fermi energy position.

Thermoelectric materials enable heat-to-electricity conversion, while its efficiency has so far been restricted by the dimensionless figure of merit ($\mathit{ZT}$). In this study, we employ first-principles calculations combined with Boltzmann transport equation along with the thermal transport unified theory to investigate the electrical and thermal transport properties of a family of Li-based chalcogenides ($\mathrm{L}{\mathrm{i}}_{3}B{X}_4, B=\mathrm{V}$, Nb, Ta and $X=\mathrm{S}$, Se, Te). It is found that $\mathrm{L}{\mathrm{i}}_3\mathrm{BT}{\mathrm{e}}_4$ exhibit ultralow lattice thermal conductivity (${\kappa }_L$) at room temperature, as lows as ∼0.1 W/mK. This is mainly attributed to the relatively weak interaction between the B and Te atom as confirmed by the small number of bonding states below the Fermi level, which introduces strong anharmonicity and significantly enhances the phonon scattering rate. Moreover, the observed power factors of $\mathrm{L}{\mathrm{i}}_3\mathrm{BT}{\mathrm{e}}_4$ are more than 10 $\mu \mathrm{W}\mathrm{c}{\mathrm{m}}^{-1}{\mathrm{K}}^{-2}$ at 300 K, giving rise to giant $\mathit{ZT}$ at intermediate and high temperatures in both p-type and n-type, for instance, $\mathit{ZT}$ reaches 2.25 ∼ 2.46 in $\mathrm{L}{\mathrm{i}}_3\mathrm{NbT}{\mathrm{e}}_4$ even after considering both particlelike propagation and wavelike phonon tunneling transport mechanism. In addition, we find that $\mathit{ZT}$ of $\mathrm{L}{\mathrm{i}}_3\mathrm{B}{\mathrm{X}}_4$ can further be enhanced through moderate strain engineering and these Li-based chalcogenides exhibit high ductility which is favorable for the post machining process. The present work unravels the importance of strong anharmonicity induced by weak-bonded heavy element on the thermoelectric performance in $\mathrm{L}{\mathrm{i}}_3\mathrm{B}{\mathrm{X}}_4$ family which provides important insights for the rational design of flexible thermoelectric devices.

Graphitic materials are widely used in thermal management owing to the high basal-plane thermal conductivity. However, the modeling and physics of basal-plane heat transport along finite-sized graphite ribbons remain to be fully established. In this work, we present a computational approach by directly solving the phonon Boltzmann transport equation in both three-dimensional real space and reciprocal space with first-principles input of phonon properties. Our theoretical model predicts the thickness- and temperature-dependent thermal conductivities of both multilayer and thin graphite ribbons in good agreement with a broad range of experiments when carefully considering the effects of finite length, width and thickness as well as the sample conditions. The observation of phonon Poiseuille flow is also shown to be very sensitive to the surface roughness of graphite ribbons, which have to be sufficiently smooth in the thickness direction. This work thus provides an efficient modeling framework for future theoretical and experimental investigations of hydrodynamic heat transport in graphitic structures.

We report a random nonequilibrium Green's function method (rNEGF) to tackle the challenge of large-scale quantum transport simulation. In this method, the rNEGF is represented with $N_s$ random superposition states of the source eigenmodes, significantly reducing the computational complexity of quantum transport properties. As a demonstration, we implement the rNEGF within the exact muffin-tin orbital-based density functional theory and calculate the electron transmission through large devices with Hamiltonian dimension up to $4\times {10}^5$ from first principles. It is found that a rather small $N_s$ (even $N_s=1$), in orders of magnitude smaller than the number of source eigenmodes, can present reliable transmission results with a relative standard deviation $\sim 1\%$. Our calculations cover the challenging transport regimes of disorder scattering and resonant tunneling. The rNEGF method only bares the statistical error and presents an important self-averaging effect with respect to the cross-section size of the device, providing an effective stochastic quantum transport approach.

It was recently suggested that proximitized gate-defined Ge hole nanowires could serve as an alternative materials platform for the realization of topological Majorana zero modes (MZMs). Here, we theoretically study the expected experimental signatures of Ge-based MZMs in tunneling conductance measurements, taking into account that unintentional random disorder is unavoidably present in realistic devices. Explicitly, we present numerically calculated local and nonlocal tunneling conductance spectra (as functions of bias voltage and magnetic field) for two different wire lengths, two different disorder models, two different parent superconductors (Al and NbTiN), and various disorder strengths, which we relate to an estimated lower bound for the disorder strength in Ge-based hybrid devices that we extract from the experimentally reported hole mobilities in current state-of-the-art two-dimensional Ge hole gases. We find that even if the actual disorder strength in the Ge-based hybrid device exceeds this theoretical lower bound by an order of magnitude, the system is still in the weak disorder regime, where the topological superconductivity is intact and the local conductance spectra manifest clear end-to-end correlated zero-bias peaks if and only if the system hosts topological end MZMs. This shows that, despite the relatively small pristine topological gaps (approximately few tens of $\mu \mathrm{eV}$), Ge-based hybrid devices are a promising alternative platform for Majorana experiments due to the extremely high materials quality, which leads to an increased gap-to-disorder ratio and, therefore, to less ambiguity in the experimental tunneling conductance data compared to InAs-based devices.

We concentrate on the topological phase transition and non-Hermitian skin effects in a spinful Su-Schrieffer-Heeger (SSH) chain by considering the presence of nonreciprocal spin-orbital coupling (NSOC). Via performing combined similarity and unitary transformation, this SSH chain is reconstructed as two nonreciprocal SSH subchains. Then, the global physical properties of this system are determined by discussing the two subchains. It is found that the system displays the topologically trivial-to-nontrivial phase transition, and the NSOC plays nontrivial roles in governing the non-Hermitian skin effect and pseudo-Hermitian symmetric phase transition. Moreover, the bipolar skin effect is allowed to come into being, with the different localization properties on the two sides of the chain. It can be believed that the findings in this work promote to understand the topological edge states and skin effects in the SSH lattices with non-Hermitian NSOCs.

The thermal Hall effect has emerged as an ideal probe for investigating topological phenomena of charge-neutral excitation. Notably, it reveals crucial aspects of spin-lattice couplings that have been difficult to access for decades. However, the exchange striction mechanism from a lattice induced change in exchange interaction has often been ignored in thermal Hall experiments. $\mathrm{MnP}{\mathrm{S}}_3$ can offer a platform to study exchange striction on the thermal Hall effect due to its significant spin-lattice coupling and field induced noncollinear spin configuration. Our thermal transport data show distinct temperature and field dependence of longitudinal thermal conductivity (${\kappa }_{xx}$) and thermal Hall effect (${\kappa }_{xy}$). By using detailed theoretical calculation, we found that the inclusion of the exchange striction is essential for a better description of both ${\kappa }_{xx}$ and ${\kappa }_{xy}$. Our result demonstrates the importance of the exchange striction mechanism for a complete understanding of the magnon-phonon-driven thermal Hall effect.

The electronic ground state of a three-dimensional (3D) band insulator with time-reversal $\left(\mathrm{\Theta }\right)$ symmetry or time-reversal times a discrete translation $\left(\mathrm{\Theta }{T}_{1/2}\right)$ symmetry is classified by a ${\mathbb{Z}}_2$-valued topological invariant and characterized by quantized magnetoelectric response. Here we demonstrate by explicit calculation in model ${\mathbb{Z}}_2$ topological insulator thin-films that whereas the magnetoelectric response is localized at the surface in the $\mathrm{\Theta }$ symmetry (nonmagnetic) case, it is nonuniversally partitioned between surface and interior contributions in the $\mathrm{\Theta }{T}_{1/2}$ (antiferromagnetic) case, while remaining quantized. Within our model the magnetic field induced polarization arises entirely from an anomalous $\mathcal{N}=0$ Landau level subspace within which the projected Hamiltonian is a generalized Su-Schrieffer-Heeger model whose topological properties are consistent with those of the starting 3D model. We identify a new connection between the ground-state geometry of that 3D model and surface-interior partitioning in thin films.

We present the results of a thorough investigation of the physical properties of ${\mathrm{EuAg}}_4{\mathrm{Sb}}_2$ single crystals using magnetization, heat capacity, and electrical resistivity measurements. High-quality single crystals, which crystallize in a trigonal structure with space group $R\overline{3}m$, were grown using a conventional flux method. Temperature-dependent magnetization measurements along different crystallographic orientations confirm two antiferromagnetic phase transitions around $T_{N1}=10.5\mathrm{K}$ and $T_{N2}=7.5\mathrm{K}$. Isothermal magnetization data exhibit several metamagnetic transitions below these transition temperatures. Antiferromagnetic phase transitions in ${\mathrm{EuAg}}_4{\mathrm{Sb}}_2$ are further confirmed by two sharp peaks in the temperature-dependent heat capacity data at $T_{N1}$ and $T_{N2}$, which shift to lower temperature in the presence of an external magnetic field. Our systematic heat capacity measurements utilizing a long-pulse and single-slope analysis technique allow us to detect a first-order phase transition in ${\mathrm{EuAg}}_4{\mathrm{Sb}}_2$ at 7.5 K. The temperature-dependent electrical resistivity data also manifest two features associated with magnetic order. The magnetoresistance exhibits a broad hump due to a field-induced metamagnetic transition. Remarkably, the magnetoresistance keeps increasing without showing any tendency to saturate as the applied magnetic field increases, and it reaches $\sim 20$ 000% at 1.6 K and 60 T. At high magnetic fields, several magnetic quantum oscillations are observed, indicating a complex Fermi surface. A large negative magnetoresistance of about $-55\%$ is also observed near $T_{N1}$. Moreover, the $H\text{−}T$ phase diagram constructed using magnetization, heat capacity, and magnetotransport data indicates complex magnetic behavior in ${\mathrm{EuAg}}_4{\mathrm{Sb}}_2$.

Many-body localization (MBL) has been proposed to enable and protect topological order in all eigenstates, vastly expanding the traditional ground-state setting. However, for the most intriguing case of two-dimensional (2D) systems with anyons and topology-dependent degeneracies, the dense many-body spectrum challenges studying this MBL protection numerically. Here we use large-scale full-spectrum variational Ansätze to demonstrate MBL-protected topological order in the disordered 2D toric code perturbed by magnetic fields. We show that the system has topological local integrals of motion (tLIOMs) for magnetic field strengths below $h_c\approx 0.1$ times the toric-code coupling scale. Combining tLIOMs with exact diagonalization, we also identify high-energy topological multiplets in the dense many-body spectrum. The phase diagram we find is consistent with toric-code and trivial MBL phases being separated by an intervening thermal phase.

Using a first-order $\mathbf{k}·\mathbf{p}$ Kane model, this work studies the impact of band-mixing, which gives rise to nonparabolicity, on electron intersubband scattering in zinc-blende semiconductor quantum well structures. The eight-band model considers both spin-flip and spin-conserving processes as well as a nonparabolic subband dispersion. We examine the effects of considering multiple band components in the total eigenstate, as well as their k-dependent properties, on LO phonon, impurity, and interface roughness (IFR) scattering. These k-dependent eigenstates account for the effects of varying wave function composition, spatial confinement and Rashba spin-orbit coupling. The angular dependencies of spin-conserving and spin-flip transitions are analyzed in the case of LO phonon emission scattering, and the heavy-hole interaction is shown to have a strong influence. The total (spin-conserving plus spin-flip) scattering is more concentrated in the forward direction than in the standard three-band $\mathbf{k}·\mathbf{p}$ model. Furthermore, the neutrality of the scattering processes versus the spin-type of the initial state is discussed and is directly linked to the structural inversion asymmetry. The overall scattering rate is notably reduced when band-mixing is included within the framework of a first-order Kane model in comparison to a standard one-band $\mathbf{k}·\mathbf{p}$ model. As an example, the total 2-to-1 LO phonon scattering decreases by up to $\sim 60\%$ in narrow InAs/AlAsSb quantum wells (${\lambda }_{21}\sim 2.7\mu \mathrm{m}$). Similarly significant reductions are also reported for IFR scattering. Interestingly, this slowing effect persists even for long wavelengths. Our results collectively emphasize the importance of band-mixing when modeling intersubband devices.

We use magnetometry, calorimetry, and high-resolution capacitive dilatometry, as well as single-crystal neutron diffraction to explore the temperature-field phase diagram of the anisotropic honeycomb magnet ${\mathrm{BaCo}}_2{\left({\mathrm{AsO}}_4\right)}_2$. Our data reveal four distinct ordered states observed for in-plane magnetic fields. Of particular interest is the narrow region between 0.51 and 0.54 T that separates the up-up-down order from the fully polarized state and coincides with the field range where signatures of the spin-liquid behavior have been reported. We show that magnetic Bragg peaks persist in this intermediate phase, thus ruling out its spin-liquid nature. However, the simultaneous nonmonotonic evolution of nuclear Bragg peaks suggests the involvement of the lattice, witnessed also in other regions of the phase diagram where large changes in the sample length are observed upon entering the magnetically ordered states. Our data highlight the importance of lattice effects in ${\mathrm{BaCo}}_2{\left({\mathrm{AsO}}_4\right)}_2$.

Magnetoelectric coupling is crucial for spintronic applications of multiferroic materials; however, it is usually rather weak. Here, we propose that strong magnetoelectric coupling could be realized by electrical control of structural phase transition and spin-lattice interaction. Our first-principles calculations reveal two inequivalent stable multiferroic phases (denoted as $2H$ and $T^{″}$ phases) in a double transition metal dichalcogenide $\mathrm{NbV}{\mathrm{S}}_4$ monolayer. The $2H$ phase is ferromagnetic, while the $T^{″}$ phase is antiferromagnetic, and their in-plane ferroelectric polarizations are orthogonal. Therefore, a 90 ° rotation of the electric polarization is realizable by applying an electric field, which transforms the structural as well as the magnetic phases, leading to a strong magnetoelectric coupling. The emergence of such multistate multiferroicity with strong magnetoelectric coupling holds promising applications in high-density low-energy-dissipation memories.