The spin Hall (SH) effect is a phenomenon in which the spin current flows perpendicular to an applied electric field and causes the spin accumulation at the boundaries. However, in the presence of spin-orbit couplings, the spin current is not well defined. Here, we calculate the spin response to an electric-field gradient, which naturally appears at the boundaries. We derive a generic formula using the Bloch wave functions and the phenomenological relaxation time. We also calculate the response for the uniform Rashba model with $\delta$-function nonmagnetic disorder within the first-order Born approximation and corresponding vertex corrections. We find the nonzero spin accumulation, although the SH conductivity exactly vanishes.

We study an experimentally feasible system of strongly correlated bosons with random hoppings described by the infinite-range Bose-Hubbard model on a lattice with hopping integrals given by independent random variables of Gaussian distribution with nonzero mean. We solve this quantum model in the thermodynamic limit, employing the replica method and the Trotter-Suzuki formula. We find and describe a superglass phase that emerges at the interface between glass and superfluid phases. Both glassy and long-range orderings are present in the superglass and compete with each other, as revealed by the anticorrelation of their order parameters. We present phase diagrams in various cross sections of the multidimensional space of system parameters. In selected parameter subspaces, we compare the results to those of nondisordered, diagonally disordered, and once celebrated spin-glass systems.

The transport statistics of the 1D chain and metallic armchair graphene nanoribbons with hopping disorder are studied, with a focus on understanding the crossover between the zero-energy critical point and the localized regime at larger energy. In this crossover region, transport is found to be described by a two parameter scaling with the ratio $s$ of system size to mean free path, and the product $r$ of energy and scattering time. This two parameter scaling shows excellent data collapse across a wide a variety of system sizes, energies, and disorder strengths. The numerically obtained transport distributions in this regime are found to be well described by a Nakagami distribution, whose form is controlled up to an overall scaling by the ratio $s/{|lnr|}^2$. For sufficiently small values of this parameter, transport appears virtually identical to that of the zero-energy critical point, while at large values, a Gaussian distribution corresponding to exponential localization is recovered. For intermediate values, the distribution interpolates smoothly between these two limits.

We describe the macroscopic behavior of superfluid ${}^3\mathrm{He}$ in the $P_1$ ($\beta$) phase in an anisotropic aerogel. It turns out that the $P_1$ phase shares many features with superfluid ${}^3\mathrm{He}\text{−}{\mathrm{A}}_1$. It exists only in an external magnetic field and has only one spin orientation in its superfluid condensate. In the $P_1$ phase, the direction of the external magnetic field, the preferred direction in orbit space $\widehat{\mathbf{m}}$ and the average preferred direction of the silica strands ${\zeta }_i$, are all parallel. While the preferred direction in orbit space and the average preferred direction of the silica strands are even under time reversal, the preferred direction $\widehat{\mathbf{w}}$ in spin space is odd under time reversal. As new macroscopic variables compared with superfluid ${}^3\mathrm{He}$ we have for the superfluid $P_1$ phase in an aerogel the strain field associated with the aerogel network. As a result of these additional macroscopic variables we find new static and dynamic cross-coupling terms, which come as reversible (zero entropy production) as well as as irreversible contributions. As an outstanding feature of the $P_1$ phase we find that second sound and, to a lesser extent, fourth sound assume spin-wave character, a feature that should be testable experimentally. This result closely parallels that for the $A_1$ phase of bulk superfluid ${}^3\mathrm{He}$ in spite of the fact that the $\widehat{\mathbf{l}}$ vector of the $A_1$ phase, which is odd under time reversal, does not exist in the $P_1$ phase. We also discuss briefly the macroscopic behavior of the distorted $\beta$ ($P_2$) phase, which shares several features with the distorted $A$ phase of bulk superfluid ${}^3\mathrm{He}$, in particular with respect to its properties in spin space.

Moiré superlattices consist of parallel but staggered periodic lattices and have been extensively explored due to their salient physical properties. However, there are limited demonstrations of such concepts for classical wave systems. Here, we construct an acoustic biaxially strained moiré superlattice by mismatching lattice constants in both $x$ and $y$ directions. The interface between two different topological regions with opposite valley Chern numbers forms a valley-induced network along which acoustic waves can travel efficiently. Taking a unit cell from the superlattice as a six-terminal device, the incoming acoustic waves can be partitioned into the left-adjacent, the right-adjacent, and the forward-facing channels. The acoustic beam splitting is protected by the valley polarization. Our results provide a comprehensive analysis of the transport properties of acoustic waves in the moiré superlattice and can provide useful insights for designing topological acoustic devices ranging from topological networks, valley filters, to energy splitters.

We propose a spatiotemporal characterization of the entanglement dynamics in many-body localized (MBL) systems, which exhibits a striking resemblance to dynamical heterogeneity in classical glasses. Specifically, we find that the relaxation times of local entanglement, as measured by the concurrence, are spatially correlated yielding a dynamical length scale for quantum entanglement. As a consequence of this spatiotemporal analysis, we observe that the considered MBL system is made up of dynamically correlated clusters with a size set by this entanglement length scale. The system decomposes into compartments of different activity such as active regions with fast quantum entanglement dynamics and inactive regions where the dynamics is slow. We further find that the relaxation times of the on-site concurrence become broadly distributed and more spatially correlated, as disorder increases or the energy of the initial state decreases. Through this spatiotemporal characterization of entanglement, our work unravels a previously unrecognized connection between the behavior of classical glasses and the genuine quantum dynamics of MBL systems.

The layered perovskite ${\mathrm{Sr}}_2\mathrm{Ru}{\mathrm{O}}_4$ is a very intensively studied superconductor, but its pairing mechanism, which is often coupled intimately with magnetic fluctuations in correlated materials, is still an open question. Here we present a systematic evolution of the Seebeck coefficient in Co- and Mn-substituted ${\mathrm{Sr}}_2\mathrm{Ru}{\mathrm{O}}_4$ single crystals, in which ferromagnetic and antiferromagnetic glassy states respectively emerge in proximity to the superconducting phase of the parent compound. We find that the Seebeck coefficient $S$ divided by temperature $T$, $S/T$, shows a maximum near characteristic temperatures seen in the irreversible magnetization $M_{\mathrm{ir}}$ in both the Co- and Mn-substituted crystals, demonstrating both the ferromagnetic and antiferromagnetic fluctuations to enhance the Seebeck coefficient. Interestingly, $S/T$ increases with lowering temperature in the parent compound, reminiscent of non-Fermi-liquid behavior, indicating an essential role of coexisting ferromagnetic and antiferromagnetic fluctuations for the itinerant electrons in ${\mathrm{Sr}}_2\mathrm{Ru}{\mathrm{O}}_4$.

Magnetoresistance in novel materials has been attracting ever-increasing attention since its mechanism is still the subject of intense debate and the physics behind these emergent phenomena remains a wild space to be explored. Here, we grow ${\mathrm{YbBi}}_2$ single crystals and study their anisotropic giant magnetoresistance and Fermi surface topology via de Haas–van Alphen oscillation and Hall resistivity measurements, electronic band structure calculations, and so on. A detailed analysis of the angle-dependent quantum oscillations reveals the presence of nontrivial topological electronic states and several cylindrical Fermi surface sheets extended along the $b$ axis. Hall resistivity data suggest that multiple charge carriers participate in the transport, and electron and hole densities are nearly balanced. These findings are further confirmed by theoretical calculations. After checking several possible mechanisms, the giant magnetoresistance ($\sim 1.2\times {10}^3\%$ at 14 T and 2 K) in ${\mathrm{YbBi}}_2$ is ascribed to the carrier compensation instead of topological protection and open orbits. Additionally, we also find that Fermi surface anisotropy serves as a key element for the angular magnetoresistance in this compound. Our studies show that ${\mathrm{YbBi}}_2$ can be not only a topologically nontrivial material, but also a prototype system to check familiar magnetoresistance mechanisms.

Topology and machine learning are two actively researched topics not only in condensed matter physics, but also in data science. Here, we propose the use of topological data analysis in unsupervised learning of the topological phase diagrams. This is possible because the quantum distance can capture the shape of the space formed by the Bloch wave functions as we sweep over the Brillouin zone. Therefore, if we minimize the volume of the space formed by the wave function through a continuous deformation, the wave functions will end up forming distinct spaces which depend on the topology of the wave functions. Combining this observation with the topological data analysis, which provides tools such as the persistence diagram to capture the topology of the space formed by the wave functions, we can cluster together Hamiltonians that give rise to similar persistence diagrams after the deformation. By examining these clusters as well as representative persistence diagrams in the clusters, we can draw the phase diagram as well as distinguish between topologically trivial and nontrivial phases. Our proposal to minimize the volume can be interpreted as finding geodesics in a one-dimensional (1D) Brillouin zone and minimal surfaces in 2D and higher-dimensional Brillouin zones. Using this interpretation, we can guarantee the convergence of the minimization under certain conditions, which is an outstanding feature of our algorithm. We demonstrate the working principles of our machine learning algorithm using various models.

Periodically modulated quantum crystals and their photonic analogs—also known as Floquet crystals (FCs)—are characterized by continuous quasienergy bands separated from each other by spectral gaps. Meanwhile, a separate class of periodically driven systems—the so-called time crystals (TCs)—have an entirely different band structure characterized by gaps in their Bloch momenta. The reasons for such starkly different properties of the FCs and TCs are uncovered and time-averaged perturbation theory is used to derive the criteria for band gaps opening in quasienergy, Bloch momentum, or both. Examples from electrodynamics and from a Su-Schrieffer-Heeger lattice model illustrate the emergence of non-Hermiticity, exceptional points, and amplified edge states in periodically driven systems.

Raman spectroscopy has become one of the most utilized methods for the characterization of transition metal dichalcogenides (TMDCs); however, the interpretation of the Raman spectra of TMDC-based heterostructures has been the subject of recent debate. Using a comprehensive combination of micro-Raman and tip-enhanced Raman spectroscopy, accompanied by ab initio simulations of both Raman frequencies and intensities, we show that the activation of the otherwise geometry-forbidden $E$ mode and symmetry-forbidden $A_1$ mode is the fingerprint of the strong interaction between the monolayer ${MX}_2$ ($M$ is Mo/W, $X$ is S/Se) and the gold substrate, in contrast to the weakly interacting or freestanding ${MX}_2$.

Fractons are particles with restricted mobility. We give a symmetry-based derivation of effective field theories of gapless phases with fractonic topological defects, such as solids and supersolids, using a coset construction. The resulting theory is identified as the Cosserat elasticity theory, which reproduces the conventional symmetric elasticity theory at low energies. The construction can be viewed as a dynamical realization of the inverse Higgs mechanism. We incorporate topological defects such as dislocations and disclinations, which are nontrivially related by the Bianchi identities of defect gauge fields. The origin of the fractonic nature of defects in those systems can be traced back to the semidirect product structure of translational and rotational groups. The construction is immediately extendable to higher dimensions and systems with broken translational symmetries, such as solids, supersolids, and vortex crystals. We identify Wess-Zumino terms in supersolids, which induce quasiparticle scatterings on topological defects.

We investigate the evolution of the Mott insulators in the triangular lattice Hubbard Model, as a function of hole doping $\delta$ in both the strong and intermediate coupling limits. Using the advanced density matrix renormalization group (DMRG) method, at light hole doping $\delta \lesssim 10\%$, we find a significant difference between strong and intermediate couplings. Notably, at intermediate coupling an unusual metallic state emerges, with short ranged spin correlations but long ranged spin-chirality order. Moreover, no clear Fermi surface or wave vector is observed, this chiral metal also exhibits staggered loop current, which breaks the translational symmetry. These features disappear on increasing interaction strength or on further doping. At strong coupling, the 120 degree magnetic order of the insulating magnet persists for light doping, and produces hole pockets with a well-defined Fermi surface. On further doping, $\delta \approx 10\%\sim 20\%$ SDW order and coherent hole Fermi pockets are found at both strong and intermediate couplings. At even higher doping $\delta \gtrsim 20\%$, the SDW order is suppressed and the spin-singlet Cooper pair correlations are simultaneously enhanced. We also briefly comment on the strong particle-hole asymmetry of the model.

We present a systematic investigation of the low-frequency charge carrier dynamics in different charge states of the organic conductors $\theta \text{−}(\mathrm{BEDT}\text{−}{\mathrm{TTF})}_{2}M\mathrm{Zn}{\left(\mathrm{SCN}\right)}_4$ with $M=\text{Rb,}\text{Tl}$, which result from quenching or relaxing the charge degrees of freedom on a geometrically frustrated triangular lattice. Due to strong electronic correlations these materials exhibit a charge-ordering transition, which can be kinetically avoided by rapid cooling resulting in a so-called charge-glass state without long-range order. The combination of fluctuation spectroscopy and a heat pulse method allows us to study and compare the resistance fluctuations in the low-resistive quenched and the high-resistive charge-ordered state, revealing striking differences in the respective noise magnitudes. For both compounds, we find strongly enhanced resistance fluctuations right at the metal-insulator transition and a broad noise maximum in the slowly cooled charge-crystal state with partly dominating two-level processes revealing characteristic activation energies.

Coherent multidimensional optical spectroscopy methods overcome some of the limitations found in their one-dimensional counterparts and allow us, for example, to resolve overlapped spectral features, to separate homogeneous and inhomogeneous broadening, and to track the energy transfer kinetics and coherent dynamics in complex quantum systems. In their most common configurations, signal detection is achieved by optical means, making these techniques widespread in studies of bulk systems but less common in the surface and interface sciences. In this paper, we demonstrate an inherently surface-sensitive two-dimensional coherent spectroscopy scheme, based on photoelectron detection, by studying the interface formed between tris(8-hydroxyquinolinato)aluminium (${\mathrm{Alq}}_3$) and a ferromagnetic Co surface. Despite the inhomogeneous linewidth broadening (≈800 meV) in the ensemble of disordered molecules, we resolve two narrow resonances (≈10 meV linewidth) with an energy spacing of ≈80 meV. By combining experimental data and simulations, using the Lindblad master equation, we identify these resonances as lowest unoccupied molecular orbital (LUMO) to $\mathrm{LUMO}+1$ transitions in chemically decoupled second-layer ${\mathrm{Alq}}_3$ molecules and deduce related optical coherence lifetimes of at least 120 and 240 fs. These observations establish that ${\mathrm{Alq}}_3$ molecules in a disordered adsorbate layer exhibit well-defined and rather homogeneous internal electronic transitions, although the absolute energetic positions of the involved states with respect to the substrate reference are significantly affected by the disorder. The results indicate that inhomogeneous line broadening in a disordered ${\mathrm{Alq}}_3$ layer and pure dephasing have only a minor impact on optical transitions in individual molecules. This opens interesting opportunities for coherent control schemes and emphasizes the importance of optical coherences for all electron dynamics, even in disordered hybrid metal-molecule interfaces.

Far from being limited to a trivial generalization of their Hermitian counterparts, non-Hermitian topological phases have gained widespread interest due to their unique properties. One of the most striking non-Hermitian phenomena is the skin effect, i.e., the localization of a macroscopic fraction of bulk eigenstates at a boundary, which underlies the breakdown of the bulk-edge correspondence. Here we develop a generic phenomenological approach to describing magnetic dissipation within a lattice model and we introduce an “effective area law” to investigate the emergence of the skin effect in magnetic systems. As a testbed of our approach, we focus on a spin-orbit-coupled van der Waals (vdW) ferromagnet with spin-nonconserving magnon-phonon interactions, finding that the magnetic skin effect emerges in an appropriate temperature regime. Our results suggest that the interference between Dzyaloshinskii-Moriya interaction (DMI) and nonlocal magnetic dissipation plays a key role in the accumulation of bulk states at the boundaries.

Single-pulse ($\sim 100$-ps duration) extended x-ray absorption fine structure (EXAFS) measurements were obtained in laser-shocked Pt to examine atomic vibrational properties and to determine temperatures for shock pressures from 72 to 325 GPa. Pt x-ray absorption spectra were recorded while a planar shock wave was propagating through the Pt sample. The absorption spectrum corresponding to the shocked Pt was obtained by subtracting the ambient Pt contribution from the measured absorption spectrum. Fits to the shocked-state EXAFS data provided Pt lattice parameters consistent with the known Pt Hugoniot and the mean-squared relative displacements (MSRDs) for nearest-neighbor Pt atoms. Pt temperatures in the shocked state, estimated from the MSRDs using the correlated Debye model and correlated Einstein models, were consistent with both the Hugoniot temperatures calculated by integration along the Hugoniot and with the Hugoniot temperatures from published first-principles calculations. However, the agreement between the Hugoniot temperatures from EXAFS measurements and the calculated Hugoniot temperatures is not as good above 200 GPa, likely due to anharmonic effects. The present results demonstrate that single-pulse synchrotron EXAFS measurements in laser-shocked solids are useful for quantitative temperature determination and for examination of vibrational properties, including anharmonicity, at extreme pressure-temperature conditions.

Angle-dispersive x-ray powder diffraction experiments have been performed on praseodymium metal to a pressure of 205 GPa. Between 20 and 165 GPa only the $oC4$ ($\alpha$-uranium) phase is observed, in agreement with previous studies. At 171(5) GPa we find a transition to a tetragonal $tI2$ phase which is isostructural with the high-pressure post-$oC4$ phase seen in the neighboring lanthanide cerium above 12 GPa, and with the high-pressure phase of the actinide thorium seen above 100 GPa. Electronic structure calculations determine the $oC4\to tI2$ transition to occur at 130 GPa at 0 K, but find another phase, with the $hP1$ (simple hexagonal) structure, to have a lower enthalpy than both the $oC4$ and $tI2$ structures above 20 GPa at 0 K.