We investigate the effect of a two-level jump process or random telegraph noise on a square wave driven tight-binding lattice. In the absence of the noise, the system is known to exhibit dynamical localization for specific ratios of the amplitude and the frequency of the drive. We obtain an exact expression for the probability propagator to study the stability of dynamical localization against telegraph noise. Our analysis shows that in the presence of noise, a proper tuning of the noise parameters destroys dynamical localization of the clean limit in one case, while it induces dynamical localization in an otherwise delocalized phase of the clean model. Numerical results help verify the analytical findings. A study of the dynamics of entanglement entropy from an initially half-filled state offers complementary perspective.

Studies of the quasi-two-dimensional organic conductors $\lambda \text{−}{\left(D\right)}_{2}M{\mathrm{Cl}}_4$ [$D=\text{donor molecules}$, $M=\mathrm{Ga},\mathrm{Fe}$] have shown that $\lambda \text{−}{\left(\mathrm{BETS}\right)}_2{\mathrm{GaCl}}_4$ [BETS = bis(ethylenedithio)tetraselenafulvalene] undergoes an unconventional superconducting transition and $\lambda \text{−}{\left(\mathrm{BETS}\right)}_2{\mathrm{FeCl}}_4$ undergoes a field-induced superconducting transition. In $\lambda$-type salts, the interactions between donor molecules and ${\mathrm{FeCl}}_4^{-}$ ($\pi \text{−}d$ interactions) are important. To investigate $\pi \text{−}d$ interaction, a pair of magnetic $M=\mathrm{Fe}$ and nonmagnetic $M=\mathrm{Ga}$ salts which have the same ground state in the donor layer is desired. However, no such pair has been found, and few experimental studies have considered $\pi \text{−}d$ interaction paths. $\lambda \text{−}{\left(\mathrm{BEST}\right)}_{2}M{\mathrm{Cl}}_4$ [BEST = bis(ethylenediseleno)tetrathiafulvalene] are obtained for both anions, and $M=\mathrm{Ga}$ salt shows an antiferromagnetic transition, but the ground state has not been analyzed in $M=\mathrm{Fe}$ salt. We perform x-ray diffraction, magnetic susceptibility measurement, and Mössbauer spectroscopy in $\lambda \text{−}{\left(\mathrm{BEST}\right)}_2{\mathrm{FeCl}}_4$. We find that a magnetic transition is observed at around 26 K. The $\lambda \text{−}{\left(\mathrm{BEST}\right)}_{2}M{\mathrm{Cl}}_4$ system is a system in which both ${\mathrm{FeCl}}_4^{-}$ and ${\mathrm{GaCl}}_4^{-}$ salts show antiferromagnetic transitions. In addition, the ethylene motions observed at room temperature are ordered around 108 K, resulting in the establishment of the $\pi \text{−}d$ interaction path between chalcogens and the anion, and low-field magnetization suggests that the $\pi \text{−}d$ interaction in $\lambda \text{−}{\left(\mathrm{BEST}\right)}_2{\mathrm{FeCl}}_4$ is smaller than that in $\lambda \text{−}{\left(\mathrm{BETS}\right)}_2{\mathrm{FeCl}}_4$. Our results show that the inner chalcogen of donor molecules is important as the path of the interaction.

We investigate valley-dependent electronic transport properties of graphene in close proximity to a thick ferromagnetic insulator (FI). It is found that spin-resolved valley filtering can be achieved under the interplay between the stray field emanated from the FI and the exchange-proximity interaction. In the intraband-tunneling regime, there exists a window of Fermi energy where both the spin and valley polarization of the output current are almost complete $(\approx -100\%)$. In the interband-tunneling regime, the valley polarization can approach $100\%$ or $-70\%$ near some conductance peaks, while the spin polarization is near $100\%$ in a wide window of Fermi energy. The role of valley-Zeeman coupling is examined for both cases. The spin-valley filtering is found to be tunable by electric gating. Our findings are helpful for designing a spin-valley filter based on graphene with imprinted ferromagnetism.

The beauty of the quantum Hall (QH) effect is the metrological precision of Hall resistance quantization that originates from the topological edge states. Understanding the factors that lead to quantization breakdown not only provides important insights on the nature of the topological protection of these edge states, but is beneficial for device applications involving such quantized transport. In this work, we combine conventional transport and real space conductivity mapping to investigate whether the quantization breakdown is tied to the disappearance of edge state in the hotly studied ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ system. Our experimental results unambiguously show that topological edge state does exist when quantization breakdown occurs. Such edge state is dissipative in nature and could lead to a quantization breakdown due to its diffusive character causing overlapping with bulk and other edge states in real devices. Our findings bring attention to issues that are generally inaccessible in the transport study of QH, but can play important roles in practical measurements and device applications.

We investigate the two-plasmon spontaneous decay of a quantum emitter near single-walled carbon nanotubes (SWCNTs) and graphene-coated wires (GCWs). We demonstrate efficient, enhanced generation of two-plasmon entangled states in SWCNTs due to the strong coupling between tunable guided plasmons and the quantum emitter. We predict two-plasmon emission rates more than twelve orders of magnitude higher than in free space, with average lifetimes of a few dozen nanoseconds. Given their low dimensionality, these systems could be more efficient for generating and detecting entangled plasmons in comparison to extended graphene. Indeed, we achieve a tunable spectrum of emission in GCWs, where sharp resonances occur precisely at the plasmons' minimum excitation frequencies. We show that by changing the material properties of the GCW's dielectric core, one could tailor the dominant modes and frequencies of the emitted entangled plasmons while keeping the decay rate ten orders of magnitude higher than in free space. By unveiling the unique properties of two-plasmon spontaneous emission processes in the presence of low-dimensional carbon-based nanomaterials, our findings set the basis for a novel material platform with applications to on-chip quantum information technologies.

The Casimir-Lifshitz torque between a pair of birefringent materials was recently shown to exhibit a change in sign with respect to the separation distance owing to the planar dielectric properties of the interacting materials. The recent experiment that verified the existence of the Casimir-Lifshitz torque precluded a sign reversal between the liquid crystal 5CB $\left(4\text{−}\mathrm{cyano}\text{−}4\text{−}n\text{−}\mathrm{pentylbiphenyl}\right)$ and calcite [Somers et al., Nature (London) 564, 386 (2018)]. Here, we will show that the sign reversal was not observed in the experiment because it would happen at a larger distance than was investigated for the pairs of materials considered. The purpose of this paper is to identify appropriate choices of combinations of materials that will facilitate experimental observation of the distance-dependent sign reversal of the torque in the experimentally feasible distance regime. Specifically, we propose a setup comprising biaxial black phosphorus and the liquid crystal 5CB or 5PCH $\left(4\text{−}\mathrm{cyano}\text{−}4\text{−}n\text{−}\mathrm{pentylcyclohexane}\text{−}\mathrm{phenyl}\right)$ as a particularly viable option. The feature of sign reversal will be an interesting addition to the control mechanism of actuation and switch devices that are applicable for the Casimir-Lifshitz torque.

Using numerically exact methods we study transport in an interacting spin chain which for sufficiently strong spatially constant electric field is expected to experience Stark many-body localization. We show that starting from a generic initial state, a spin excitation remains localized only up to a finite delocalization time, which depends exponentially on the size of the system and the strength of the electric field. This suggests that bona fide Stark many-body localization occurs only in the thermodynamic limit. We also demonstrate that the transient localization in a finite system and for electric fields stronger than the interaction strength can be well approximated by a Magnus expansion up to times which grow with the electric field strength.

The interplay between disorder and interactions can dramatically influence the physical properties of thin-film superconductors. In the most extreme case, strong disorder is able to suppress superconductivity as an insulating phase emerges. Due to the known pair-breaking potential of magnetic disorder on superconductors, the research focus is on the influence of nonmagnetic disorder. Here we provide direct evidence that magnetic disorder is also present at the surface of amorphous superconducting films. This magnetic disorder is present even in the absence of magnetic impurity atoms and is intimately related to the surface termination itself. While bulk superconductivity survives in sufficiently thick films, we suggest that magnetic disorder may crucially affect the superconductor-to-insulator transition in the thin-film limit.

We present results for the entire set of anomalous charge and heat transport coefficients for metallic systems in the presence of a finite-temperature heat bath. In realistic physical systems, this necessitates the inclusion of inelastic dissipation mechanisms; relatively little is known theoretically about their effects on anomalous transport. Here we demonstrate how these dissipative processes are strongly intertwined with Berry-curvature physics. Our calculations are made possible by the introduction of a Caldeira-Leggett reservoir, which allows us to avoid the sometimes-problematic device of the pseudogravitational potential. Using our formulas, we focus on the finite-temperature behavior of the important anomalous Wiedemann-Franz ratio. Despite previous expectations, this ratio is found to be nonuniversal as it can exhibit either an upturn or a downturn as temperature increases away from zero. We emphasize that this derives from a competition between Berry curvatures having different signs in different regions of the Brillouin zone. We point to experimental support for these observations and for the behavior of an alternative ratio involving a thermoelectric response which, by contrast, appears to be more universal at low temperatures. Our work paves the way for future theory and experiment, demonstrating how inelastic scattering at nonzero temperature affects the behavior of all anomalous transport coefficients.

The physical properties of itinerant antiferromagnetic (AFM) ${\mathrm{SrCr}}_2{\mathrm{As}}_2$ with body-centered tetragonal ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure were investigated in single crystalline and polycrystalline forms by electrical resistivity $\rho$, heat capacity $C_{\mathrm{p}}$, magnetic susceptibility $\chi$ versus temperature $T$, and magnetization $M$ versus applied magnetic field $H$ isotherm measurements as well as ${}^{75}\mathrm{As}$ and ${}^{53}\mathrm{Cr}$ nuclear magnetic resonance (NMR) measurements in the wide temperature range $T$ = 1.6–900 K. From the $\chi \left(T\right)$ and ${}^{75}\mathrm{As}$ NMR measurements, the G-type AFM state below $T_{\mathrm{N}}$ = 615(15) K has been determined, consistent with the previous neutron-diffraction measurements. Direct evidence of magnetic ordering of the Cr spins was shown by the observation of the ${}^{53}\mathrm{Cr}$ NMR spectrum under $H$ = 0. From the $\chi \left(T\right)$ measurements on single-crystal ${\mathrm{SrCr}}_2{\mathrm{As}}_2$ under the two different magnetic field directions $H\left|\right|ab$ and $H\left|\right|c$ in the AFM state, the Cr ordered moments are shown to align along the $c$ axis in the G-type AFM state. The metallic state is directly evidenced by the $\rho , C_{\mathrm{p}}$, and NMR measurements, and the density of states at the Fermi energy $\mathcal{D}\left(E_{\mathrm{F}}\right)$ in the AFM state is estimated to be 7.53 states/eV f.u. for both spin directions which is almost twice the bare $\mathcal{D}\left(E_{\mathrm{F}}\right)$ estimated from first-principles calculations, suggesting an enhancement of the conduction-carrier mass by a factor of two in the AFM state. The $\mathcal{D}\left(E_{\mathrm{F}}\right)$ is found to be nearly constant below at least 100 K and is independent of $H$. The $\rho \left(T\right)$ is found to show $T$-linear behavior above $T_{\mathrm{N}}$ and exhibits positive curvature below $T_{\mathrm{N}}$ where significant loss of spin-disorder scattering upon magnetic ordering is observed. The resistivity anisotropy of the compound remains moderate ${\rho }_c/{\rho }_a\sim 9$ through most of the magnetically ordered phase but shows a rapid increase below 50 K.

Quantum spin-1/2 system, in which spin, electric, and elastic subsystems are coupled, is studied analytically. We have shown that the external magnetic and electric field and strain, which reduce the symmetry, can affect many observable characteristics of the system. The analysis reveals how quantum critical values of the governing parameters can manifest themselves in the temperature behavior of those observables. Predicted effects can be useful for application in many fields of microelectronics.

Here we report a resonant x-ray diffraction (RXD) study at the Cu $L_3$ edge on the multichiral system ${\mathrm{CsCuCl}}_3$, exhibiting helical magnetic order in a chiral crystal structure. RXD is a powerful technique to disentangle electronic degrees of freedom due to its sensitivity to electric monopoles (charge), magnetic dipoles (spin), and electric quadrupoles (orbital). We characterize electric quadrupole moments around Cu ascribed to the unoccupied Cu $3d$ orbital, whose quantization axis is off the basal plane. Detailed investigation of magnetic reflections reveals additional sinusoidal modulations along the principal axis superimposed on the reported helical structure, i.e., a longitudinal conical (helical-butterfly) structure. The out-of-plane modulations imply significant spin-orbit interaction despite $S=1/2$ of ${\mathrm{Cu}}^{2+}$.

We report a combined theoretical and experimental study of a novel quaternary Heusler system, CoFeVSb, from the viewpoint of room-temperature spintronics and thermoelectric applications. CoFeVSb crystallizes in a cubic structure with a small $\mathrm{D}{\mathrm{O}}_3$-type disorder. The presence of the disorder is confirmed by room-temperature synchrotron x-ray diffraction and extended x-ray absorption fine structure measurements. Magnetization data reveal a high ordering temperature $(\sim 850\mathrm{K})$ with a saturation magnetization of 2.2 ${\mu }_B/\mathrm{f}.\mathrm{u}.$ Resistivity measurements indicate a half-metallic or semimetallic nature. A double hysteresis loop along with asymmetry in the magnetoresistance data reveals a room-temperature spin valve feature, which remains stable even at 300 K. Hall measurements show anomalous behavior with a significant contribution from the intrinsic Berry phase. This alloy also has a large room-temperature power factor ($\sim 0.62 \mathrm{mW}{\mathrm{m}}^{-1}{\mathrm{K}}^{-2}$) and ultralow simulated lattice thermal conductivity ($\sim 0.4 \mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$), making it a promising candidate for thermoelectric application. Ab initio calculations suggest weak spin-polarized semimetallic behavior and reduced magnetization (in agreement with the experiment) in the presence of $\mathrm{D}{\mathrm{O}}_3$ disorder. We have also found an energetically competing ferromagnetic (FM)/antiferromagnetic interface structure within an otherwise FM matrix, one of the prerequisites for spin valve behavior. The coexistence of so many promising features in a single system is rare, and hence CoFeVSb gives a fertile platform to explore numerous applications in the future.

We predict that long-range triplet correlations (LRTC) in superconductor/ferromagnet (S/F) hybrids with extrinsic impurity spin-orbit coupling can be generated and manipulated by supercurrent flowing in the superconducting leads along the S/F interfaces. The LRTC appear via two basic mechanisms. The essence of the first one is the generation of triplets by the superconducting spin Hall effect. These pairs are long range in the ferromagnet under the appropriate mutual orientation of the condensate momentum and the ferromagnet magnetization. The second mechanism is based on the singlet-triplet conversion at the S/F interface followed by the rotation of the spin of the obtained short-range opposite-spin pairs via the spin current swapping mechanism. The structure of the supercurrent-induced LRTC is studied both for S/F bilayers and superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions. We demonstrate that in S/F/S junctions, where the Josephson coupling is realized via the supercurrent-induced LRTC, the ground state phase can be switched between 0 and $\pi$ in a controllable manner. The switching is performed by reversing the supercurrent in one of the superconducting leads, thus realizing a physical principle of the $\text{0-}\pi$ shifter.

We investigate the evolution of structural parameters, optical properties, and electronic structures of the van der Waals kagome semiconductor ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ with Se doping. When the doping level of Se increases, the band gaps of ${\mathrm{Pd}}_3{\mathrm{P}}_2{\left({\mathrm{S}}_{1-x}{\mathrm{Se}}_x\right)}_8$ single crystals decrease gradually, accompanied by the expanded unit cells. First-principles calculations show that there is a flat band (FB) near the Fermi level in bulk ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$. This FB mainly originates from the $d_{z^2}$-like orbitals of Pd atoms in the Pd kagome lattice, which has finite interlayer electron hopping perpendicular to the ${\mathrm{PdS}}_4$ square plane. The interlayer hopping can be reinforced with Se doping, inducing a stronger interlayer coupling via the chalcogen atoms at apical sites, which reduces the band gap and enhances the cleavage energy. In contrast, the vanishing interlayer hopping in the two-dimensional limit results in the formation of an ultra-FB in the monolayers of these compounds. The easy exfoliation and the existence of a unique ultra-FB near $E_{\mathrm{F}}$ make ${\mathrm{Pd}}_3{\mathrm{P}}_2{\left({\mathrm{S}}_{1-x}{\mathrm{Se}}_x\right)}_8$ a model system to explore the exotic physics of a FB in a two-dimensional kagome lattice.

We report here the properties of single crystals of ${\mathrm{La}}_5{\mathrm{AgPb}}_3$, which is a member of the $R_{5}M{X}_3$ ($R$ = rare earth, $M$ = transition metal or main group element, $X=\mathrm{Pb}$, Sn, Sb, In, Bi) family of chainlike compounds. Measurements of the electrical resistivity, specific heat, and magnetic susceptibility are compared to the results of density functional calculations, finding that ${\mathrm{La}}_5{\mathrm{AgPb}}_3$ is a nonmagnetic metal with moderate correlations. The analysis of the electrical resistivity and specific heat measurements highlight the importance of lattice vibrations in the material, while the calculated electron density suggests the presence of localized La and well-hybridized Ag orbitals that extend along the $c$ axis in the ${\mathrm{La}}_5{\mathrm{AgPb}}_3$ structure. The temperature dependence of the magnetic susceptibility is consistent with a possible one-dimensional character of ${\mathrm{La}}_5{\mathrm{AgPb}}_3$, where the strength of correlations is much weaker than in one-dimensional conductors that have been previously reported.

We formulate a general criterion that underlies the persistence of conductance zeros induced by destructive quantum interference under the application of external perturbations in physical systems described by a discrete nonsingular Hamiltonian $H$. Our approach uses nonzero matrix elements of $H^{-1}$ between two lattice points as edges of a graph to indicate the existence of a nonzero conductance between the same points. A given conductance zero, or a missing edge in the inverted graph, is preserved when the perturbation, in the form of on-site or additional interpoint hopping energies, is applied only to points outside the set of first-order graph neighbors of either the entry lead or the exit lead. We discuss the application of these results to a study of the robustness of the conductance zeros in the fulvene and benzene molecules.

The tensors of conductivity and spin susceptibility of a two-dimensional electron gas (2DEG) with equal Rashba and Dresselhaus spin-orbit interaction constants [the persistent spin helix (PSH) state] in a parallel magnetic field are calculated. Applying a parallel magnetic field to the PSH state leads to the appearance of a saddle point in the spectrum and, accordingly, to a Van Hove singularity (VHS), whose amplitude increases indefinitely as the magnetic field strength $\left(\mathbf{b}\right)$ approaches to some critical value $b_{cr}$. The presence of a VHS in the density of states is an important factor determining the conductivity and spin susceptibility tensors. When only the lower spin subband is filled, the off-diagonal elements of the conductivity tensor are nonzero; that is, a Hall voltage arises due to the anisotropy of the Fermi surface and scattering. In the region where two spin subbands are filled, the diagonal and off-diagonal components of the spin susceptibility tensor are equal, and the off-diagonal terms of the conductivity tensor vanish. A sharp decrease in the conductivity and spin susceptibility at the beginning of the filling of the second spin subband, the ratio of the diagonal component of the spin susceptibility to the off-diagonal one, and also the number of critical points in the spectrum make it possible to establish the PSH 2DEG state.