The magnetic, electronic, and thermal properties of ${\mathrm{Fe}}_3{\mathrm{Ge}}_2\mathrm{Sb}$ single crystals, a derivative of the hexagonal FeGe structure with a buckled Fe kagome net and Sb-Sb dimers are reported. Electronic structure calculations show most of the kagome-derived bands remain intact with the Fe buckling, with the exception of a van Hove singularity near the Fermi level, which is selectively destroyed. This selective destruction of the van Hove singularity is associated with the lack of a charge order transition in ${\mathrm{Fe}}_3{\mathrm{Ge}}_2\mathrm{Sb}$ compared to FeGe. Magnetization measurements show two antiferromagnetic transition at 290 K and 16 K. The low-temperature transition is attributed to spin canting and is associated with a metamagnetic transition observed in the isothermal magnetization below the transition temperature. Electrical and thermal transport measurements show metallic behavior, and more significant magnetic scattering associated with the metamagnetic transition is observed in the magnetothermal conductivity compared to the magnetoresistance. This is consistent with a modification of the long-period magnetic structure that modifies preferentially small angle scattering thus having a strong impact on thermal transport properties. We conclude that buckled ${\mathrm{Fe}}_3{\mathrm{Ge}}_2\mathrm{Sb}$ exhibits similar properties to unbuckled hexagonal FeGe with the exception of the lack of a charge density wave transition in ${\mathrm{Fe}}_3{\mathrm{Ge}}_2\mathrm{Sb}$, likely due to the selective destruction of the van Hove singularity near ${\mathrm{E}}_F$, making the family of compounds ${\mathrm{Fe}}_3{\mathrm{Ge}}_{3-x}{\mathrm{Sb}}_x$ a good host to study various physical effects in kagome metals, especially the electronic and structural stabilization of charge ordered states.

We solve numerically the large-$N$ Dyson-Schwinger equations for the Sachdev-Ye-Kitaev (SYK) model utilizing the Legendre polynomial decomposition and reaching ${10}^{-36}$ accuracy. Using this we compute the energy of the SYK model at low temperatures $T\ll J$ and obtain its series expansion up to $T^{7.54}$. While it was suggested that the expansion contains terms $T^{3.77}$ and $T^{5.68}$, we find that the first noninteger power of temperature is $T^{6.54}$, which comes from the two-point function of the fermion bilinear operator $O_{h_1}=\chi {\partial }_{\tau }^3\chi$ with scaling dimension $h_1\approx 3.77$. The coefficient in front of $T^{6.54}$ term agrees well with the prediction of the conformal perturbation theory. We conclude that the conformal perturbation theory appears to work even though the SYK model is not strictly conformal.

We investigate the quantum quench dynamics of the interacting Hatano-Nelson model with open boundary conditions using both Abelian bosonization and numerical methods. Specifically, we follow the evolution of the particle density and current profile in real space over time by turning the imaginary vector potential on or off in the presence of weak interactions. Our results reveal spatiotemporal Friedel oscillations in the system with light cones propagating ballistically from the open ends, accompanied by local currents of equal magnitude for both switch-off and -on protocols. Remarkably, the bosonization method accurately accounts for the density and current patterns with a single overall fitting parameter. The continuity equation is satisfied by the long-wavelength part of the density and current, despite the nonunitary time evolution when the Hatano-Nelson term is switched on.

We present an angle-resolved photoemission spectroscopy study of the single-layer T*-type structured cuprate ${\mathrm{SmLa}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ with unique fivefold pyramidal oxygen coordination. Upon varying oxygen content, T*-${\mathrm{SmLa}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ evolved from a Mott-insulating to a metallic state where the Luttinger sum rule breaks down under the assumption of a large holelike Fermi surface. This is in contrast with the known doping evolution of the structural isomer ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ with sixfold octahedral coordination. In addition, quantitatively characterized Fermi surface suggests that the empirical $T_{\mathrm{c}}$ rule for octahedral oxygen-coordination systems does not apply to T*-${\mathrm{SmLa}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$. The present results highlight unique properties of the T*-type cuprates possibly rooted in its oxygen coordination, and necessitate thorough investigation with careful evaluation of disorder effects.

In recent years the ergodicity of disordered spin chains has been investigated via extensive numerical studies of the level statistics or the transport properties. However, a clear relationship between these results has yet to be established. We present the relation between the diffusion constant and the energy-level structure, which leads to the Thouless localization criterion. Together with the exponential-like dependence of the diffusion constant on the strength of quasiperiodic or random fields, the Thouless criterion explains the nearly linear drift with the system size of the crossover/transition to the nonergodic regime. Moreover, we show that the Heisenberg spin chain in the presence of the quasiperiodic fields can be well approached via a sequence of simple periodic systems, where diffusion remains finite even at large fields.

We show that anomalous Floquet topological insulators generate intrinsic, non-Hermitian topology on their boundaries. As a consequence, removing a boundary hopping from the time-evolution operator stops the propagation of chiral edge modes, leading to a non-Hermitian skin effect. This does not occur in Floquet Chern insulators, however, in which boundary modes continue propagating. The non-Hermitian skin effect on the boundary is a consequence of the nontrivial topology of the bulk Floquet operator, which we show by designing a real-space topological invariant. In this paper, we introduce a form of mixed higher-order topology, providing a bridge between research on periodically driven systems and the study of non-Hermiticity. This suggests that periodic driving, which has already been demonstrated in a wide range of experiments, may be used to generate non-Hermitian skin effects.

We investigated the electronic structure of the antiferromagnetic Kondo lattice ${\mathrm{CePd}}_5{\mathrm{Al}}_2$ using high-resolution angle-resolved photoemission spectroscopy. The experimentally determined band structure of the conduction electrons is predominated by the Pd $4d$ character. It contains multiple hole and electron Fermi pockets, in good agreement with density functional theory calculations. The Fermi surface is folded over ${\mathit{Q}}_0=(0,0,1)$, manifested by Fermi surface reconstruction and band folding. Our results suggest that Fermi surface nesting drives the formation of antiferromagnetic order in ${\mathrm{CePd}}_5{\mathrm{Al}}_2$.

The experimental evidence of the ultrahigh electron mobility and strong spin-orbit coupling in the two-dimensional (2D) layered bismuth-based oxyselenide, ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$, makes it a potential material for spintronic devices. However, its spin-related properties have not been extensively studied due to the centrosymmetric nature of its crystal structure. By using first-principles density-functional theory calculation, this study reports the emergence of Rashba-spin-valley states in ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ monolayer (ML). Breaking the crystal inversion symmetry of ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ ML using an external electric field enables the Rashba-spin-valley formation, causing the appearance of the Rashba-type splitting around the $\mathrm{\Gamma }$ valley and spin-valley coupling at the $D$ valleys located near the middle of $\mathrm{\Gamma }-M$ line. In addition to the typical Rashba-type spin textures around the $\mathrm{\Gamma }$ valley, the study also observed in-plane unidirectional spin textures around the $D$ valleys, which is a rare phenomenon in 2D materials. The observed Rashba-spin-valley states are driven by the lowering point group symmetry of the crystal from $D_{4h}$ to $C_{4v}$ enforced by the electric field, as clarified through $\vec{k}·\vec{p}$ model derived from symmetry analysis. More importantly, tuning the Rashba and spin-valley states by using biaxial strain offers a promising route to regulate the spin textures and spin splitting preventing the electron from back-scattering in spin transport. Finally, we proposed a more realistic system, namely, ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}\mathrm{ML}/\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ (001) heterointerface that supports the strong Rashba-spin-valley states and highlighting the potential of the ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ ML for future spintronics and valleytronics-based devices.

At geomagnetic field strengths, polymer organic light-emitting diodes (OLEDs) exhibit a giant anisotropy in magnetoresistance of up to 35%. Comparison of the effect arising from a protonated and an equivalent perdeuterated conjugated polymer, in combination with semiclassical quantum-stochastic modeling, demonstrates that microscopically anisotropic hyperfine-field distributions, on the level of the individual molecules, constitute the primary cause for this effect. For this microscopic anisotropy to emerge in the ensemble there must also be some degree of macroscopic ordering, which may arise from the structural anisotropy of the polymer. The theory predicts a critical field range, for which the anisotropy transitions from a twofold to a fourfold and back to a twofold angular functionality with increasing field strength, over a field range of only a few microtesla. Such a transition is indeed found experimentally, although it spans over a somewhat larger field range, suggesting a level of material disorder that is not accounted for in the simulations. Through the combination with microscopic modeling, anisotropic magnetoresistance can serve as a sensitive probe of macroscopic molecular ordering in organic semiconductors. The inclination compass effect in OLEDs also offers a potential route for probing the radical-pair mechanism of spin chemistry in the solid state, and the associated coherent and incoherent electronic and nuclear spin dynamics at room temperature, and could point to an intriguing analogy to some forms of avian magnetoreception.

Using a combination of experiment and simulation, we study the magnetotransport in a two-dimensional disordered Lorentz gas with circular obstacles. Our focus is on the investigation of the Hall effect at obstacle densities beyond the low-density limit. However, as a reference, we also consider very low obstacle densities. Here, the magnetotransport properties, as obtained from the simulation and the experiment of a pristine sample, can be well described in terms of the Drude-Boltzmann model. For intermediate and high obstacle density, only for very low magnetic fields $B$, we find a linear dependence of the Hall resistance ${\varrho }_{xy}$ on $B$, albeit with a Hall coefficient that does not reflect properly the carrier density. At larger magnetic fields but still below the onset of the Landau quantization as well as the magnetic-field-induced conductor-to-insulator transition, striking nonlinearities of ${\varrho }_{xy}\left(B\right)$ due to classical memory effects are observed. Moreover, the scattering time obtained within the Drude-Boltzmann model develops into a phenomenological parameter that decreases with increasing magnetic field.

Structural and electronic properties of silicon and germanium monolayers with two different diamondoid crystal structures are detailed ab initio. Our results show that, despite Si and Ge being well-known indirect gap semiconductors in their bulk form, their adamantane and diamantane monolayers can exhibit optically active direct gap in the visible frequency range, with highly anisotropic effective masses, depending on the monolayer crystal structure. Moreover, we reveal that gaps in these materials are highly tunable with applied strain. These stable monolayer forms of Si and Ge are therefore expected to help bridging the gap between the fast growing area of opto-electronics in two-dimensional materials and the established silicon-based technologies.

Recently, electron transport along chiral molecules has been attracting extensive interest and a number of intriguing phenomena have been reported in recent experiments, such as the emergence of zero-bias conductance peaks in the transmission spectrum upon the adsorption of single-helical protein on superconducting films. Here, we present a theoretical study of electron transport through a two-terminal single-helical protein sandwiched between a superconducting electrode and a normal-metal one in the presence of a perpendicular magnetic field. As the proximity-induced superconductivity attenuates with the distance from superconducting media, the pairing potential along the helix axis of the single-helical protein is expected to decrease exponentially, which is characterized by the decay exponent $\lambda$ and closely related to the experiments. Our results indicate that (i) a zero-bias conductance peak of $2e^2/h$ appears at zero temperature and the peak height (width) decreases (broadens) with increasing temperature, and (ii) this zero-bias peak can split into two peaks, which are in agreement with the experiments [see, e.g., H. Alpern et al. Nano Lett. 19, 5167 (2019)]. Remarkably, Majorana zero modes are observed in this protein-superconductor setup in a wide range of model parameters, as manifested by the $Z_2$ topological invariant and the Majorana oscillation. Interestingly, a specific region is demonstrated for decaying superconductivity, where topologically nontrivial and trivial zero modes coexist and the bandgap remains constant. With increasing the pairing potential, the topologically nontrivial zero modes will transform to the trivial ones without any bandgap closing-reopening, and the critical pairing potential of the phase transition attenuates exponentially with $\lambda$. Additionally, one of the two zero modes can be continuously shifted from one end of the protein toward the other end contacted by the normal-metal electrode. The underlying physics of the topologically nontrivial and trivial zero modes is discussed.

Superexchange is one of the vital resources to realize long-range interaction between distant spins for large-scale quantum computing. Recent experiments have demonstrated coherent oscillations between logical states defined by remote spins whose coupling is given by the superexchange interaction mediated by central spins. Excavating the potential of superexchange requires a full understanding of the interaction in terms of control parameters, which is still lacking in literature. Here, using full configuration interaction calculations, we study a two-electron system in a linear triple-quantum-dot device in which the left and right dots are occupied by a single electron each, whose spin states are defined as qubits. The numerical nature of the full configuration interaction calculations allows access to the microscopic details of the quantum-dot confining potential and electronic wave functions, some of which are overlooked in the celebrated Hubbard model but turn out to be critical for the behavior of superexchange. Following experimental demonstrations of superexchange interactions, we focus on the detuning regime where the charge ground state yields an empty middle dot. We have found that, when the detunings at the left and right dots are leveled, the superexchange can exhibit a nonmonotonic behavior, which ranges from positive to negative values as a function of the middle-dot detuning. We further show that a larger relative detuning between the left and right dots causes the magnitude of the superexchange to increase (decrease) for an originally positive (negative) superexchange. We then proceed to show the results for a much larger left-right dot detuning. Using a Hubbard-like model, we present analytical expressions of the superexchange and have found that they conform well qualitatively with the numerical results. Our results suggest that even a simple configuration of delocalized two-electron states in a linear triple-quantum-dot device exhibits superexchange energy with nontrivial behaviors, which could have important applications in spin-based quantum computing.

Bloch waves in one-dimensional periodic systems carry the Zak phase, which plays a key role in determining the band topology. In general, for a system that possesses inversion symmetry, the Zak phase of an isolated band is quantized as 0 or $\pi$ and is associated with the spatial-field symmetries of the Bloch waves at the Brillouin-zone center and boundary. Since the radiation losses from leaky systems are strongly associated with the Bloch waves, one may probe the far-field continuum to determine the Zak phases. Here, we formulate the radiations from photonic systems in Fourier space at the zone center and boundary and find they reveal the field symmetries and thereby the corresponding Zak phase. For verification, we have studied the Zak phases of TM plasmonic and TE photonic crystals by electrodynamic simulations and measuring the topologically properties of plasmonic crystals using Fourier-space optical spectroscopy and common-path interferometry. In addition, a topologically protected interface state is demonstrated when two topologically trivial and nontrivial systems are joined together. Our results provide a simple way for characterizing the band topology of photonic systems via far fields.

A simple effective screening parameter for the screened range-separated exchange-correlation hybrid functional is constructed from the compressibility sum rule, in the context of the linear-response time-dependent density functional theory. When applied to the dielectric-dependent hybrid (DDH), it becomes remarkably accurate for bulk solids, compared to those obtained from fitting with the model dielectric function or depending on the valence electron density of materials. The present construction of the screening parameter is simple and realistic. The screening parameter developed in this way is physically appealing and practically useful as it is straightforward to obtain using the average of the local Seitz radius over the unit-cell volume of the bulk solid. Furthermore, we have obtained a very good accuracy for energy band gaps, positions of the occupied $d$ bands, ionization potentials, optical properties of semiconductors and insulators, and geometries of bulk solids (equilibrium lattice constants and bulk moduli) from the constructed DDH.

The discovery of correlated insulating states in moiré heterostructures has renewed the interest in strongly coupled electron systems where spin and valley (or layer) degrees of freedom are intertwined. In the strong-coupling limit, such systems can be effectively described by SU(4) spin-valley models akin to Kugel-Khomskii models long studied in the context of spin-orbit coupled materials. However, typical moiré heterostructures also exhibit interactions that break the SU(4) symmetry down to SU(2)${}_{\mathrm{spin}}\otimes \mathrm{U}$(1)${}_{\mathrm{valley}}$. Here we investigate the impact of such symmetry-breaking couplings on the magnetic phase diagram for triangular superlattices considering a filling of two electrons (or holes) per moiré unit cell. We explore a broad regime of couplings—including XXZ anisotropies, Dzyaloshinskii-Moriya exchange, and on-site Hund's couplings—using semiclassical Monte Carlo simulations. We find a multitude of classically ordered phases, including (anti)ferromagnetic, incommensurate, and stripe order, manifesting in different sectors of the spin-valley model's parameter space. Zooming in on the regimes where quantum fluctuations are likely to have an effect, we employ pseudofermion functional renormalization group (pf-FRG) calculations to resolve quantum disordered ground states such as spin-valley liquids, which we indeed find for certain parameter regimes. As a concrete example, we discuss the case of trilayer graphene aligned with hexagonal boron nitride using material-specific parameters.

We explore the effect of heat treatment in argon atmosphere under various temperatures up to $500{}^{\circ }\mathrm{C}$ on single crystals of $\alpha \text{−}{\mathrm{RuCl}}_3$ by the study of the mass loss, microprobe energy-dispersive x-ray spectroscopy, powder x-ray diffraction, and electrical resistance, as well as low-temperature magnetic susceptibility and specific heat. Clear signatures of dechlorination and oxidation of Ru appear for annealing temperatures beyond $300{}^{\circ }\mathrm{C}$. Analysis of the specific heat below 2 K reveals a ${\mathrm{RuO}}_2$ mass fraction of order $1\%$ for pristine $\alpha \text{−}{\mathrm{RuCl}}_3$ which increases up to $20\%$ after thermal annealing, fully consistent with mass-loss analysis. The small ${\mathrm{RuO}}_2$ inclusions drastically reduce the global electrical resistance and may thus significantly affect low-temperature thermal transport and Hall effect.

Recent studies have demonstrated that measures of tripartite entanglement can probe data characterizing topologically ordered phases to which bipartite entanglement is insensitive. Motivated by these observations, we compute the reflected entropy and logarithmic negativity, a mixed-state entanglement measure, in tripartitions of bosonic topological orders using the anyon diagrammatic formalism. We consider tripartitions in which three subregions meet at trijunctions and tetrajunctions. In the former case, we find a contribution to the negativity that distinguishes between Abelian and non-Abelian order while in the latter, we find a distinct universal contribution to the reflected entropy. Finally, we demonstrate that the negativity and reflected entropy are sensitive to the $F$ symbols for configurations in which we insert an anyon trimer, for which the Markov gap, defined as the difference between the reflected entropy and mutual information, is also found to be nonvanishing.

The Nielson-Ninomiya theorem states that a chirally invariant free fermion lattice action, which is local, translation invariant, and real, necessarily has fermion doubling. The SLAC approach gives up on locality, and long-range hopping leads to a linear dispersion with singularity at the zone boundary. We introduce a SLAC Hamiltonian formulation that is expected to realize a U(1) helical Luttinger liquid in a naive continuum limit. We argue that nonlocality and concomitant singularity at the zone edge have important implications. Large momentum transfers yield spurious features already in the noninteracting case. Upon switching on interactions, nonlocality invalidates the Mermin-Wagner theorem and allows for long-ranged magnetic ordering. In fact, in the strong-coupling limit the model maps onto an XXZ-spin chain with $1/r^2$ exchange. Here, both spin-wave and DMRG calculations support long-ranged order. While the long-ranged order opens a single-particle gap at the Dirac point, the singularity at the zone boundary persists for any finite value of the interaction strength such that the ground state remains metallic. Hence, the SLAC Hamiltonian does not flow to the 1D helical Luttinger liquid fixed point. Aside from DMRG simulations, we have used auxiliary field quantum Monte Carlo simulations to arrive at the above conclusions.

We study theoretically the polarization dynamics in a ring-shape bosonic condensate of exciton-polaritons confined in a rotating trap. The interplay between the rotating potential and TE-TM splitting of polariton modes offers a tool of control over the spin state and the angular momentum of the condensate. Specific selection rules describing the coupling of pseudospin and angular momentum are formulated. The resonant coupling between states having linear and circular polarizations leads to the polarization beats. The effect may be seen as a polariton analogy to the electronic magnetic resonance in the presence of constant and rotating magnetic fields. Remarkably, spin beats are induced by a purely mechanical rotation of the condensate.