We report the measurement and analysis of weak antilocalization in ${\mathrm{Pb}}_{1-x}{\mathrm{Sn}}_x\mathrm{Se}$ topological quantum wells in a regime where the elastic scattering length is larger than the magnetic length. We achieve this regime through the development of high-quality epitaxy and doping of topological crystalline insulator quantum wells. We obtain elastic scattering lengths that exceed 100 nm and become comparable to the magnetic length. In this transport regime, the Hikami-Larkin-Nagaoka model is no longer valid. We employ the model of Wittmann and Schmid to extract the coherence time from the magnetoresistance. We find that despite our improved transport characteristics, the coherence time may be limited by scattering channels that are not strongly carrier dependent, such as electron-phonon or defect scattering.

We present a nonchiral version of the intermediate long-wave (ILW) equation that can model nonlinear waves propagating on two opposite edges of a quantum Hall system, taking into account interedge interactions. We obtain exact soliton solutions governed by the hyperbolic Calogero-Moser-Sutherland (CMS) model, and we give a Lax pair, a Hirota form, and conservation laws for this new equation. We also present a periodic nonchiral ILW equation, together with its soliton solutions governed by the elliptic CMS model.

In this paper, we use electrically detected optical excitation spectroscopy of individual erbium ions in silicon to determine their optical and paramagnetic properties simultaneously. We demonstrate that this high spectral resolution technique can be exploited to observe interactions typically unresolvable in silicon using conventional spectroscopy techniques due to inhomogeneous broadening. In particular, we resolve the Zeeman splitting of the ${}^4\mathrm{I}_{15/2}$ ground and ${}^4\mathrm{I}_{13/2}$ excited state separately, and in strong magnetic fields, we observe the anticrossings between Zeeman components of different crystal-field levels. We discuss the use of this electronic detection technique to aid in the identification of the symmetry and structure of erbium sites in silicon.

Symmetry forbidden effects in crystals may emerge in a local environment that breaks the symmetries. Yet these hidden physical effects were only discussed in centrosymmetric crystals. Here we propose that hidden physical effects can be generalized to almost all crystallographic symmetric groups and hence reveal their universality and diversity. We systematically discuss certain symmetries in crystals that may induce hidden spin polarization (HSP), hidden Berry curvature, and hidden valley polarization, with a focus on a specific pattern of HSP whose winding directions of the in-plane spin vectors are the same for adjacent bands, dubbed anomalous HSP. Such an unprecedented spin pattern arises from relatively weak spin-dependent intersector interaction and is demonstrated in mirror-symmetric InSe by first-principles calculations. Unique electric field dependent splitting into specific spatial polarization patterns may serve as an experimental signature of anomalous HSP. Our results reveal abundant hidden physical effects beyond centrosymmetric crystals and provide platforms to discuss them for emergent physical effects and future applications.

We performed a resonant inelastic x-ray scattering (RIXS) study of ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_{4+\delta }$ (LSNO) at the oxygen $K$ edge to investigate the nature of the doped holes with regard to charge excitations. Charge excitations of the hole-doped nickelates are found to be almost independent of momentum transfer, indicating that the doped holes are strongly localized in character. Additionally, conspicuous changes in energy position are in temperature dependence. These characters are observed in stark contrast to those of the high-$T_c$ cuprate ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (LSCO), where delocalized doped holes form charge excitations with sizable momentum dependence in the ${\mathrm{CuO}}_2$ plane. This distinct nature of charge excitations of doped holes is consistent with the metallicity of the materials and could be caused by strong electron-phonon coupling and weak quantum spin fluctuation in the nickelates.

A previous work [Joshi et al., Phys. Rev. X 10, 021033 (2020)] found a deconfined critical point at nonzero doping in a $t\text{−}J$ model with all-to-all and random hopping and spin exchange and argued for its relevance to the phenomenology of the cuprates. We extend this model to include all-to-all and random density-density interactions of mean-square strength $K$. In a fixed realization of the disorder, and for specific values of the hopping, exchange, and density interactions, the model is supersymmetric, but we find no supersymmetry after independent averages over the interactions. Using the previously developed renormalization group analysis, we find a new fixed point at nonzero $K$. However, this fixed point is unstable toward the previously found fixed point at $K=0$ in our perturbative analysis. We compute the exponent characterizing local density fluctuations at both fixed points: This exponent determines the spectrum of electron energy-loss spectroscopy.

Electron-phonon coupling in monolayer graphene breaks the adiabatic Born-Oppenheimer approximation and could lead to exotic logarithmic Kohn anomaly, manifested as logarithmic singularity in optical-phonon energy. However, unraveling unambiguously the fascinating logarithmic Kohn anomaly in monolayer graphene remains challenging due to the large carrier inhomogeneity originating from the unique massless Dirac-like band dispersion and the underneath substrate doping effect. Here we demonstrate a clear signature of intriguing logarithmic Kohn anomaly in monolayer graphene with ultralow carrier inhomogeneity via $h\text{−}\mathrm{BN}$ encapsulation. Significantly, the magnitude of anomalous phonon softening at 25 K shows an enhancement factor of 2 as compared to that previously observed in bilayer graphene at 12 K, even though bilayer graphene with nearly parabolic band dispersion is more immune to charged impurities. The uncovered unusual logarithmic Kohn anomaly in monolayer graphene can provide a firm basis for the understanding of various peculiar physics and may shed light on the nature of superconductivity in magic-angle graphene superlattices.

We study the magnetic-field dependence of Landau levels in graphene proximitized by large spin-orbit coupling materials, such as transition-metal dichalcogenides or topological insulators. In addition to the Rashba coupling, two types of intrinsic spin-orbit interactions, uniform (Kane-Mele type) and staggered (valley Zeeman type), are included to resolve their interplay with magnetic orbital effects. Employing a continuum model approach, we derive analytic expressions for low-energy Landau levels, which can be used to extract local orbital and spin-orbit coupling parameters from scanning probe spectroscopy experiments. We compare different parameter regimes to identify fingerprints of relative and absolute magnitudes of intrinsic spin-orbit coupling in the spectra. The inverted band structure of graphene proximitized by ${\mathrm{WSe}}_2$ leads to an interesting crossing of Landau states across the bulk gap at a crossover field, providing insights into the size of Rashba spin-orbit coupling. Landau-level spectroscopy can help to resolve the type and signs of the intrinsic spin-orbit coupling by analyzing the symmetry in energy and number of crossings in the Landau fan chart. Finally, our results suggest that the strong response to the magnetic field of Dirac electrons in proximitized graphene can be associated with extremely large self-rotating magnetic moments.

This work demonstrates that Kirchhoff's law of radiation, stating that the spectral directional emissivity and absorptivity of a surface are equal at thermal equilibrium, can be violated in planar surfaces without an external magnetic field or structures such as gratings. Modeling a type-I magnetic Weyl semimetal with an antisymmetric dielectric tensor, we show an intrinsic violation of Kirchhoff's law due to nonreciprocal surface polaritons induced by the Berry curvature and anomalous Hall velocity. This work provides a simple way to physically realize the violation of Kirchhoff's law.

We study a model of an isothermal steady-state work-to-work converter, where a single quantum two-level system (TLS) driven by time-dependent periodic external fields acts as the working medium and is permanently put in contact with a thermal reservoir at fixed temperature $T$. By combining short-iterative Lanczos (SIL) method and analytic approaches, we study the converter performance in the linear response regime and in a wide range of driving frequencies, from weak to strong dissipation. We show that for our ideal quantum machine several parameter ranges exist where a violation of thermodynamics uncertainty relations (TUR) occurs. We find the violation to depend on the driving frequency and on the dissipation strength, and we trace it back to the degree of coherence of the quantum converter. We eventually discuss the influence of other possible sources of violation, such as non-Markovian effects during the converter dynamics.

Generating irreducible site-occupancy configurations by taking advantage of crystal symmetry is a ubiquitous method for the acceleration of disordered structure prediction, which plays an important role in condensed matter physics and material science. Here, we present an algorithm for generating irreducible site-occupancy configurations, which works for arbitrary parent cells with any supercell expansion matrix, and for any number of atom types with arbitrary stoichiometry. The algorithm identifies the symmetrically equivalent configurations by searching the space group operations of the underlying lattice and building the equivalent atomic matrix based on it. Importantly, an integer representation of configurations can greatly accelerate the speed of elimination of duplicate configurations, resulting in a linear scale of run time with the number of irreducible configurations that are finally found. Moreover, based on our algorithm, we write the corresponding code named disorder in fortran programming language, and the performance test results show that the time efficiency of our disorder code is superior to that of other related codes (supercell, enumlib, and SOD).

Since the first experimental observation of the phonon Hall effect (PHE) in 2005, its physical origin and theoretical explanation have been extensively investigated. While spin-orbit interactions are believed to play important roles under external magnetic fields, nonmagnetic effects are also possible. Here we propose a mechanism of PHE which is induced by electric current in a nonequilibrium system through electron-phonon interactions. The influence of the drift electrons to the phonon degrees of freedom, as a correction to the Born-Oppenheimer approximation, is represented by an antisymmetric matrix which has the same form as in a typical phonon Hall model. We demonstrate the idea with a graphenelike hexagonal lattice having a finite phonon Hall conductivity under a driven electric current.

We propose a scheme of decomposition of the total relativistic energy in solids to intra- and interatomic contributions. The method is based on a site variation of such fundamental constant as the speed of light. As a practical illustration of the method, we tested such decomposition in the case of a spin-orbit interaction variation for the decomposition of the magnetic anisotropy energy (MAE) in CoPt. We further studied the ${\alpha }^{″}\text{−}{\mathrm{Fe}}_{16}{\mathrm{N}}_2$ magnet doped by Bi, Sb, Co, and Pt atoms. It was found that the addition of Pt atoms can enhance the MAE by as much as five times while Bi and Sb substitutions double the total MAE. Using the proposed technique, we demonstrate the spatial distribution of these enhancements. Our studies also suggest that Sb, Pt, and Co substitutions could be synthesized by experiments.

We have performed ab initio pseudopotential calculations of the structural, electronic, elastic, mechanical, vibrational, electron-phonon interaction, and superconducting properties of ScRuSi and ZrRhSi. An assessment of their elastic and mechanical properties reveals that ScRuSi is a ductile compound, while ZrRhSi is a brittle compound. For both compounds electronic energy bands in the vicinity of the Fermi level originate from the $d$ states of transition-metal atoms. The Eliashberg spectral function reveals that low-frequency phonon modes due to coupled motions of transition-metal atoms are more involved in the process of scattering of electrons than the high-frequency modes due to the vibrations of Si atoms. The average electron-phonon coupling parameter is calculated to be 0.54 for ScRuSi and 0.84 for ZrRhSi from the integration of the Eliashberg spectral function. It is found that the relatively weaker electron-phonon interaction in ScRuSi makes its superconducting transition temperature value $(T_c=3.23 \mathrm{K})$ considerably lower than that of ZrRhSi $(T_c=10.45 \mathrm{K})$.

We present coupled electron-ion Monte Carlo results for the principal Hugoniot of deuterium together with an accurate study of the initial reference state of shock-wave experiments. We discuss the influence of nuclear quantum effects, thermal electronic excitations, and the convergence of the potential energy surface by wave-function optimization within variational Monte Carlo and projection quantum Monte Carlo methods. Compared to a previous study, our calculations also include low pressure-temperature ($P,T$) conditions resulting in close agreement with experimental data, while our revised results at higher ($P,T$) conditions still predict a more compressible Hugoniot than experimentally observed.

Layered magnetic materials with nontrivial spin configurations usually emerge novel magnetic and transport properties. Herein, we investigate the anisotropy of magnetic properties and the anomalous Hall effect (AHE) in the layered itinerant ferromagnetic (FM) monoclinic ${\mathrm{Cr}}_5{\mathrm{Te}}_8\left(m\text{−}{\mathrm{Cr}}_5{\mathrm{Te}}_8\right)$ single crystal. There are some observations: (1) Based on the measurement of angular-dependent magnetization $M\left(\phi \right)$, the system shows strong twofold out-of-plane symmetry. Meanwhile, the maximum of the rotational magnetic entropy change $\mathrm{\Delta }{S}_M^{\mathrm{R}}(T,H)$ between the $c$ axis and the $ab$ plane is about $1.1\mathrm{J}{\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ with a magnetic-field change of 4.5 T. Both indicate that there exists a strong uniaxial anisotropy in $m\text{−}{\mathrm{Cr}}_5{\mathrm{Te}}_8$. (2) The paramagnetic-FM phase-transition temperature ($T_{\mathrm{C}}$) of $m\text{−}{\mathrm{Cr}}_5{\mathrm{Te}}_8$ is about 186 K and very sensitive to the applied pressure ($P$) with the derivative of $T_{\mathrm{C}}$ with respect to $Pd{T}_{\mathrm{C}}/dP\sim -50\mathrm{K}{\mathrm{GPa}}^{-1}$. (3) As to the AHE, by considering the scaling behavior between the anomalous Hall resistivity ${\rho }_{xy}^{\mathrm{A}}$ and the longitudinal resistivity ${\rho }_{xx}$, the origin of the AHE in $m\text{−}{\mathrm{Cr}}_5{\mathrm{Te}}_8$ can be described by the skew-scattering mechanism. Moreover, the measurements of the AHE and isothermal magnetization confirm that the spin-flop behavior exists in $m\text{−}{\mathrm{Cr}}_5{\mathrm{Te}}_8$. The critical field $H_{\mathrm{C}}$ is about 0.26 T, and a possible explanation is given with the magnetic phase diagram of $m\text{−}{\mathrm{Cr}}_5{\mathrm{Te}}_8$ drawn.

Results are reported for single crystals of the PbFCl-type layered compound ${\mathrm{ZrP}}_{1.27}{\mathrm{Se}}_{0.73}$ that were produced using the iodine vapor transport method. Electrical transport, magnetization, and heat capacity measurements reveal disordered metallic behavior and the occurrence of bulk superconductivity, with a transition temperature $\left(T_c\right)$ of 7.1 K and an anisotropic orbitally limited upper critical field. ${}^{31}\mathrm{P}$ nuclear magnetic resonance measurements provide additional microscopic information, where the line shape, Knight shift, and spin-lattice relaxation data are consistent with the superconductivity originating from the corrugated Zr-P(2c)/Se plane. This suggests that the superconductivity first forms in the corrugated plane and the bulk superconductivity eventually occurs via coupling between the square planar layers. These data also show that either there are multiple superconducting gaps or there is a single gap that does not fully open across the entire Fermi surface. These results clarify the superconducting state in this material and will enable further measurements that require single-crystal specimens.

Since spin can be regarded as a dummy degree of freedom, light-element topological semimetals (TSMs) are expected to be a promising alternative for spin-orbit-coupling based TSMs, which usually contain costly and toxic heavy elements. Using first-principles calculations combined with a bottom-up assembly strategy, herein we identify an intriguing light-element TSM, termed 3D borophene, which can be obtained by stacking synthesized 2D triangular borophene along the perpendicular direction. Under the protection of mirror symmetry, the linear band crossings between $\mathrm{B}-p_{xz}$ and $p_y$ states in the vicinity of the Fermi energy form two Weyl nodal lines running across the Brillouin zone in the $k_y=0$ plane. When the nodal lines are projected on the (010) surface, drumheadlike surface states and open Fermi arcs are observed, which provide vital evidence for experimental identification. Remarkably, by examining the defined slope index of the crossing bands in all possible $\mathit{k}$ paths, we find that the nodal lines of 3D borophene are composed of type-II Weyl points due to the emergence of tilted Weyl cones. Our findings not only establish a lightweight Weyl-nodal-line semimetal, but also highlight a bottom-up assembly strategy for designing desirable TSMs from synthetic 2D materials.

The exact solution of Kitaev's spin-$1/2$ honeycomb spin-liquid model has sparked an intense search for Mott insulators hosting bond-dependent Kitaev interactions, of which ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ and $\alpha \text{−}\mathrm{Ru}{\mathrm{Cl}}_3$ are prime examples. Subsequently, it has been proposed that also spin-1 and spin-$3/2$ analogs of Kitaev interactions may occur in materials with strong spin-orbit coupling. As a minimal model to describe these Kitaev materials, we study the Heisenberg-Kitaev Hamiltonian in a consistent $1/S$ expansion, with $S$ being the spin size. We present a comprehensive study of this model in the presence of an external magnetic field applied along two different directions, [001] and [111], for which an intricate classical phase diagram has been reported. In both settings, we employ spin-wave theory in a number of ordered phases to compute phase boundaries at the next-to-leading order in $1/S$ and show that quantum corrections substantially modify the classical phase diagram. More broadly, our work presents a consistent route to investigate the leading quantum corrections in spin models that break spin-rotational symmetry.