Calculations suggest that ordered Heusler alloys with 18 valance electrons could exhibit a variety of unusual electronic and magnetic states that are absent in the constituent elements. They include magnetic semiconductors, spin gapless semiconductors, compensated ferrimagnetic half-metals, and metallic antiferromagnets. Magnetic order has been predicted at exceptionally high temperature. Any of this would be of interest for spin electronics. Here, we investigate the magnetic properties of bulk, single-phase ${\mathrm{V}}_3\mathrm{Al}$, CrVTiAl and the corresponding Ga compounds, with and without ${}^{57}\mathrm{Fe}$ doping. Results are compared with data on the constituent elements. We conclude that all the as-cast alloys show some degree of B2-type ordering, but all of them are Pauli paramagnets with dimensionless susceptibilities close to the average of the atomic constituents. Prolonged annealing of the single-phase as-cast alloys leads to phase segregation. Density functional theory calculations on ${\mathrm{V}}_{3}X$ and $\text{CrVTi}X$ with $X=B$, Al, Ga, and In confirm that different atomic arrangements on the four interpenetrating face-centered cubic sublattices of the Heusler structure could indeed lead to unusual magnetic properties, but both magnetism and semiconductivity are destroyed by disorder. The energy and entropy differences between different ordered magnetic phases preclude the stabilization of any single one of them. All are metastable and inaccessible in alloys prepared from the melt.

We perform density functional theory (DFT) calculations of five solid phases and the liquid phase of tin. The calculations include cold curves of the five solid phases, phonon calculations in the quasiharmonic approximation over a range of volumes for each solid phase, and DFT-based molecular dynamics (DFT-MD) simulations of the liquid phase, including those of the melt curve using the $Z$ method. Using the DFT results, we construct a tabular multiphase sesame equation of state for tin, referred to as sesame 2162. Comparisons to experimental data are made and show a high level of agreement in isobaric data, isothermal data, shock data, and phase boundary measurements, including measurements of the melt curve. The 2162 EOS will be useful for hydrodynamics simulations and has been designed with an eye toward hydrodynamics simulations that incorporate materials strength models and allow for modeling of the kinetics of phase transitions.

In the prospect of realizing bulk superconductivity in a topological insulator, metal-doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ has been investigated with increased interest, where the Cu-, Sr-, and Nb-doped systems appear particularly promising. It is generally assumed that metal intercalation into the van der Waals (vdW) gap is responsible for the superconductivity. We have investigated the local structure of Nb in samples with nominal composition ${\mathrm{Nb}}_{0.25}{\mathrm{Bi}}_2{\mathrm{Se}}_3$ and ${\mathrm{Nb}}_{0.25}{\mathrm{Bi}}_{1.75}{\mathrm{Se}}_3$ using the x-ray absorption fine structure technique. It is found that that Nb is primarily located in a local environment consistent with that of the misfit layered structure ${\left(\mathrm{BiSe}\right)}_{1+\delta }{\mathrm{NbSe}}_2$, which has a $\delta$-dependent superconducting transition in the same temperature range. We explore the possibility of Nb occupancy on various sites in the ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ structure, but neither intercalation nor substitution lead to physically meaningful improvements of the models. Furthermore, we report single crystal x-ray diffraction analysis of Nb-doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. Difference density maps are found to show negligible occupancy in the vdW gap. The misfit layer compound has recently been suggested as an alternative origin for superconductivity in the Nb-doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ system, in good agreement with the present study. Our findings stress the necessity of thorough structural characterization of these samples. In more general terms, it raises the question of whether metal intercalation is responsible for the superconductivity in the Cu- and Sr-doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ systems or phase segregation plays a role as well.

We study transport in a one-dimensional boundary-driven Anderson insulator (the XX spin chain with onsite disorder) with randomly positioned onsite dephasing, observing a transition from diffusive to subdiffusive spin transport below a critical density of sites with dephasing. This model is intended to mimic the passage of an excitation through (many-body) insulating regions or ergodic bubbles, therefore providing a toy model for the diffusion-subdiffusion transition observed in the disordered Heisenberg model by Žnidarič et al. [Phys. Rev. Lett. 117, 040601 (2016)]. We also present the exact solution of a semiclassical model of conductors and insulators introduced by Agarwal et al. [Phys. Rev. Lett. 114, 160401 (2015)], which exhibits both diffusive and subdiffusive phases, and qualitatively reproduces the results of the quantum system. The critical properties of both models, when passing from diffusion to subdiffusion, are interpreted in terms of “Griffiths effects.” We show that the finite-size scaling comes from the interplay of three characteristic lengths: one associated with disorder (the localization length), one with dephasing, and the third with the percolation problem defining large, rare, insulating regions. We conjecture that the latter, which grows logarithmically with system size, may potentially be responsible for the fact that heavy-tailed resistance distributions typical of Griffiths effects have not been observed in subdiffusive interacting systems.

The theoretical inception of the Kitaev honeycomb model has had defining influence on the experimental hunt for quantum spin liquids, bringing unprecedented focus onto the synthesis of materials with bond-directional interactions. Numerous Kitaev materials, which are believed to harbor ground states parametrically close to the Kitaev spin liquid, have been investigated since. Yet, in these materials the Kitaev interaction often comes hand in hand with off-diagonal $\mathrm{\Gamma }$ interactions—with the competition of the two potentially giving rise to a magnetically ordered ground state. In an attempt to aid future material investigations, we study the phase diagram of the spin-1/2 Kitaev-$\mathrm{\Gamma }$ model on the honeycomb lattice. Employing a pseudofermion functional renormalization group (pf-FRG) approach, which directly operates in the thermodynamic limit and captures the joint effect of thermal and quantum fluctuations, we unveil the existence of extended parameter regimes with emergent incommensurate magnetic correlations at finite temperature. We supplement our results with additional calculations on a finite cylinder geometry to investigate the impact of periodic boundary conditions on the incommensurate order, thereby providing a perspective on previous numerical studies on finite systems.

Herein we present a study on the interplay of chemical composition with respect to $x$ in antiferromagnetic ${\mathrm{Co}}_x\mathrm{Nb}{\mathrm{S}}_2$ and the anomalous Hall effect (AHE) in the magnetically ordered state. The AHE diminishes virtually completely in samples with exceeding Co content compared to the idealized composition of $x=1/3$. For stoichiometric samples the effect is weak but shows a sign reversal just below the magnetic ordering temperature. With increasing deficiency, the magnitude of the AHE compared to the ordinary Hall effect increases and additionally an exchange-biaslike effect can be observed. The results reveal the chemical composition of the samples as tuning parameter for the AHE in ${\mathrm{Co}}_x\mathrm{Nb}{\mathrm{S}}_2$. Accompanying first-principles calculations demonstrate that the electronic band structure is only slightly affected by disorder and deficiency of Co, but an impact on the magnetic exchange coupling can be inferred. The results are interesting for the research on $3d$-metal inserted transition-metal dichalcogenides and in a broader context for the understanding and design of antiferromagnet-based spintronic materials.

We study several exotic systems, including the X-cube model, on a flat three-torus with a twist in the $xy$ plane. The ground-state degeneracy turns out to be a sensitive function of various geometrical parameters. Starting from a lattice, depending on how we take the continuum limit, we find different values of the ground-state degeneracy. Yet, there is a natural continuum limit with a well-defined (though infinite) value of that degeneracy. We also uncover a surprising global symmetry in $2+1$ and $3+1$ dimensional systems. It originates from the underlying subsystem symmetry but the way it is realized depends on the twist. In particular, in a preferred coordinate frame, the modular parameter of the twisted two-torus $\tau ={\tau }_1+i{\tau }_2$ has rational ${\tau }_1=k/m$. Then, in systems based on $\text{U}\left(1\right)\times \text{U}\left(1\right)$ subsystem symmetries, such as momentum and winding symmetries or electric and magnetic symmetries, this symmetry is a projectively realized ${\mathbb{Z}}_m\times {\mathbb{Z}}_m$, which leads to an $m$-fold ground state degeneracy. In systems based on ${\mathbb{Z}}_N$ symmetries, like the X-cube model, each of these two ${\mathbb{Z}}_m$ factors is replaced by ${\mathbb{Z}}_{gcd(N,m)}$.

Janus monolayer materials, as the thinnest materials that may possess strong Rashba spin-orbit coupling, are helpful for the miniaturization of the charge-spin conversion devices. Using first-principles calculations, we investigated the structural stability and Rashba spin-orbit coupling of distorted $1T\text{-phase}$ Janus monolayer WSSe. Although the W atoms rotating around the Se atom are dynamically unstable in the stress-free state, the imaginary frequency disappears by applying a small compressive strain. From the perspectives of macroscopic charge transfer and microscopic atomic orbital compositions, the mechanism of the Rashba spin-orbit coupling strength of the distorted $1T\text{-phase}$ Janus monolayer WSSe was analyzed. The coupling strength can be greatly manipulated when −5 to 5% biaxial strain is applied. The charge transfer caused by the larger lattice constant and the rotation of the W atoms reduce the gradient of the potential so that the greater the electric polarization, the weaker the spin-orbit coupling. The coupling strength of different electronic states is determined by the proportion of the out-of-plane atomic orbitals, where $d_{\mathrm{x}z}$ and $d_{yz}$ orbits play the dominant role. These results contribute to the design of materials with greater Rashba spin-orbit coupling and the understanding of its mechanism.

Luttinger semimetals have quadratic band crossings at the Brillouin-zone center in three spatial dimensions. Coulomb interactions in a model that describes these systems stabilize a nontrivial fixed point associated with a non-Fermi liquid state, also known as the Luttinger-Abrikosov-Beneslavskii phase. We calculate the optical conductivity $\sigma \left(\omega \right)$ and the dc conductivity ${\sigma }_{dc}\left(T\right)$ of this phase, by means of the Kubo formula and the Mori-Zwanzig memory matrix method, respectively. Interestingly, we find that $\sigma \left(\omega \right)$, as a function of the frequency $\omega$ of an applied ac electric field, is characterized by a small violation of the hyperscaling property in the clean limit, which is in contrast with the low-energy effective theories that possess Dirac quasiparticles in the excitation spectrum and obey hyperscaling. Furthermore, the effects of weak short-ranged disorder on the temperature dependence of ${\sigma }_{dc}\left(T\right)$ give rise to a stronger power-law suppression at low temperatures compared to the clean limit. Our findings demonstrate that these disordered systems are actually power-law insulators. Our theoretical results agree qualitatively with the data from recent experiments performed on Luttinger semimetal compounds like the pyrochlore iridates $\left[{\left({\mathrm{Y}}_{1-x}{\mathrm{Pr}}_x\right)}_2{\mathrm{Ir}}_2{\mathrm{O}}_7\right]$.

Every now and then one hears in the molecular electronics community that asymmetric couplings (${\mathrm{\Gamma }}_s\ne {\mathrm{\Gamma }}_t$) of the dominant level (molecular orbital) to electrodes ($s$ and $t$) which typically have shapes different from each other may be responsible for current rectification observed in experiments. Using a general single level model going beyond the Lorentzian transmission limit, in this work we present a rigorous demonstration that this is not the case. In particular, we deduce an analytical for the bias ($V$)–driven shift of the level energy $\delta {\varepsilon }_0\left(V\right)$ showing that $\delta {\varepsilon }_0\left(V\right)/V$ scales as ${\mathrm{\Gamma }}_t/W_t-{\mathrm{\Gamma }}_s/W_s$, which is merely a tiny quantity because the electrode bandwidths $W_{s,t}$ are much larger than ${\mathrm{\Gamma }}_{s,t}$. This result invalidates a previous, never deduced formula used in some previous publications that neither could be justified theoretically nor is supported by experiment. Toward the latter aim, we present new experimental evidence adding to that already inferred in earlier analyses.

Level attraction can appear in driven systems where instead of repulsion, two modes coalesce in a region separated by two exceptional points. This behavior was proposed for optomechanical and optomagnonic systems, and recently it was observed for dissipative cavity magnon-polaritons. We demonstrate that such a regime exists in a spin-orbit torque system where a magnetic oscillator is resonantly coupled to an electron reservoir. An instability mechanism necessary for mode attraction can be provided by applying an electric field. The field excites interband transitions between spin-orbit split bands leading to an instability of the magnetic oscillator. Two exceptional points then appear in the oscillator energy spectrum and the region of instability. We discuss conditions under which this can occur, and we estimate the electric field strength necessary for reaching the attraction region for a spin-orbit torque oscillator with Rashba coupling. A proposal for experimental detection is made using magnetic susceptibility measurements.

The intrinsic antiferromagnetic topological insulator $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ undergoes a metamagnetic transition in a $c$-axis magnetic field. It has been predicted that ferromagnetic $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ is an ideal Weyl semimetal with a single pair of Weyl nodes. Here we report measurements of quantum oscillations detected in the field-induced ferromagnetic phase of $\mathrm{Mn}{\mathrm{Bi}}_{2-x}{\mathrm{Sb}}_x{\mathrm{Te}}_4$, where Sb substitution tunes the majority carriers from electrons to holes. Single-frequency Shubnikov–de Haas oscillations were observed in a wide range of Sb concentrations ($0.54\le x\le 1.21$). The evolution of the oscillation frequency and the effective mass shows reasonable agreement with the Weyl semimetal band structure of ferromagnetic $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ predicted by density functional calculations. Intriguingly, the quantum oscillation frequency shows a strong temperature dependence, indicating that the electronic structure depends sensitively on magnetism.

Co-based shandite ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ is a representative example of magnetic Weyl semimetals showing rich transport phenomena. We thoroughly investigate magnetic and transport properties of hole-doped shandites ${\mathrm{Co}}_3{\mathrm{In}}_x{\mathrm{Sn}}_{2-x}{\mathrm{S}}_2$ by first-principles calculations. The calculations reproduce nonlinear reduction of anomalous Hall conductivity with doping In for ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ as reported in experiments against the linearly decreased ferromagnetic moment within virtual crystal approximation. We show that a drastic change in the band parity character of Fermi surfaces, attributed to the nodal rings lifted energetically with In doping, leads to strong enhancement of anomalous Nernst conductivity with reversing its sign in ${\mathrm{Co}}_3{\mathrm{In}}_x{\mathrm{Sn}}_{2-x}{\mathrm{S}}_2$.

We demonstrate that total reflection hard x-ray photoelectron spectroscopy (TR-HAXPES) is a versatile method for elucidating a difference between surface and bulk electronic states of strongly correlated electron systems, complementing conventional bulk sensitive hard x-ray photoelectron spectroscopy (HAXPES). To demonstrate the experimental feasibility of the method, we investigated ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_3$ and the electron-doped high-$T_{\mathrm{C}}$ superconductor ${\mathrm{La}}_{1.9}{\mathrm{Ce}}_{0.1}{\mathrm{CuO}}_4$. From the incident angle dependence of the spectral line shapes, we found that the surface-sensitive TR-HAXPES measurement equivalent to soft x-ray photoelectron spectroscopy is possible in the total reflection condition. The results strongly suggest that this method allows us to measure both surface and bulk electronic states without making any changes to experimental setup such as the energy resolution, x-ray energy, and the beamline.

We present the full magnetic $g$ tensors of the ${}^6\mathrm{H}_{5/2}{\mathrm{Z}}_1$ and ${}^4\mathrm{G}_{5/2}{\mathrm{A}}_1$ electronic states for both crystallographic sites in ${\mathrm{Sm}}^{3+}$:${\mathrm{Y}}_2{\mathrm{SiO}}_5$, deduced through the use of Raman heterodyne spectroscopy performed along nine different crystallographic directions. The maximum principle $g^{\prime }$ values were determined to be 0.447 (site 1) and 0.523 (site 2) for the ground state and 2.490 (site 1) and 3.319 (site 2) for the excited state. The determination of these $g$ tensors provide essential spin Hamiltonian parameters that can be utilized in future magnetic and hyperfine studies of ${\mathrm{Sm}}^{3+}$:${\mathrm{Y}}_2{\mathrm{SiO}}_5$, with applications in quantum information storage and communication devices.

Motivated by recent experiments on the phonon contribution to the thermal Hall effect in the cuprates, we present an analysis of chiral phonon transport. We assume the chiral behavior arises from a nonzero phonon Hall viscosity, which is likely induced by the coupling to electrons. Phonons with a nonzero phonon Hall viscosity have an intrinsic thermal Hall conductivity, but Chen et al. [Phys. Rev. Lett. 124, 167601 (2020)] have argued that a significantly larger thermal Hall conductivity can arise from an extrinsic contribution which is inversely proportional to the density of impurities. We solve the Boltzmann equation for phonon transport and compute the temperature ($T$) dependence of the thermal Hall conductivity originating from skew scattering off pointlike impurities. We find that the dominant source for thermal Hall transport is an interference between impurity skew-scattering channels with opposite parity. The thermal Hall conductivity $\sim T^{d+2}$ at low $T$ in $d$ dimensions, and has a window of $T$-independent behavior for $T>T_{\mathrm{imp}}$, where $T_{\mathrm{imp}}$ is determined by the ratio of scattering potentials with opposite parity. We also consider the role of nonspecular scattering off the sample boundary, and find that it leads to negligible corrections to thermal Hall transport at low $T$.

We consider XY-spin degrees of freedom on an fcc lattice, such that the system respects some subsystem global symmetry. We then gauge this global symmetry and study the corresponding $U\left(1\right)$ gauge theory on the fcc lattice. Surprisingly, this $U\left(1\right)$ gauge theory is dual to the original spin system. We also analyze a similar ${\mathbb{Z}}_N$ gauge theory on that lattice. All these systems are fractonic. The $U\left(1\right)$ theories are gapless and the ${\mathbb{Z}}_N$ theories are gapped. We analyze the continuum limits of all these systems and present free continuum Lagrangians for their low-energy physics. Our ${\mathbb{Z}}_2$ fcc gauge theory is the continuum limit of the well-known checkerboard model of fractons. Our continuum analysis leads to a straightforward proof of the known fact that this theory is dual to two copies of the ${\mathbb{Z}}_2$ X-cube model. We find new models and new relations between known models. The ${\mathbb{Z}}_N$ fcc gauge theory can be realized by coupling three copies of an anisotropic model of lineons and planons to a certain exotic ${\mathbb{Z}}_2$ gauge theory. Also, although for $N=2$ this model is dual to two copies of the ${\mathbb{Z}}_2$ X-cube model, a similar statement is not true for higher $N$.

In correlated electron systems the metallic character of a material can be strongly suppressed near an integer concentration of conduction electrons as Coulomb interactions forbid the double occupancy of local atomic orbitals. While the Mott-Hubbard physics arising from such on-site interactions has been largely studied, several unexplained phenomena observed in correlated materials challenge this description and call for the development of new ideas. Here we explore a general route for obtaining correlated behavior that is decidedly different from the spin-related Mott-Hubbard mechanism and instead relies on the presence of unscreened, long-range Coulomb interactions. We find a pseudogap metal phase characterized by a divergent quasiparticle mass and the opening of a Coulomb pseudogap in the electronic spectrum. The destruction of the Fermi-liquid state occurs because the electrons move in a nearly frozen, disordered charge background, as collective charge rearrangements are drastically slowed down by the frustrating nature of long-range potentials on discrete lattices. The present pseudogap metal realizes an early conjecture by Efros, that a soft Coulomb gap should appear for quantum lattice electrons with strong unscreened interactions due to self-generated randomness.