In this paper, we show that a periodically driven Aubry-André-Harper model with imbalanced on-site gain/loss supports universal one-way transport that is immune to impurities and independent of initial excitations. We reveal the underlying mechanism that the periodic driving gives rise to the non-Hermitian skin effect in the effective Floquet Hamiltonian, thereby causing universal nonreciprocal transport. Additionally, we probe the time-average decay rate of the propagator under long-time bulk dynamics as a signature of the Floquet emergent non-Hermitian skin effect. Our results provide a feasible and controllable way to realize universal one-way transport that is easily accessible to experiments.

Frustrated magnets offer a plethora of exotic magnetic ground states, including quantum spin liquids (QSLs), in which enhanced quantum fluctuations prevent a long-range magnetic ordering of the strongly correlated spins down to lowest temperature. Here we have investigated the trimer based mixed valence hexagonal rhodate ${\mathrm{Ba}}_4{\mathrm{NbRh}}_3{\mathrm{O}}_{12}$ using a combination of dc and ac magnetization, electrical resistivity, specific heat, and muon spin rotation/relaxation ($\mu \mathrm{SR}$) measurements. Despite the substantial antiferromagnetic exchange interactions, as evident from the Weiss temperature (${\theta }_{\mathrm{W}}\sim -35$ to $-45\mathrm{K}$), among the Rh-local moments, neither long-range magnetic ordering nor spin freezing is observed down to at least 50 mK, in ac-susceptibility, specific heat, and zero-field $\mu \mathrm{SR}$ measurements (down to 0.26 K). We ascribe the absence of any magnetic transition to enhanced quantum fluctuations as a result of geometrical frustration arising out of the edge-sharing equilateral Rh-triangular network in the structure. Our longitudinal-field $\mu \mathrm{SR}$ result evidences persistent spin fluctuations down to 0.26 K, thus stabilizing a dynamic QSL ground state in ${\mathrm{Ba}}_4{\mathrm{NbRh}}_3{\mathrm{O}}_{12}$. Furthermore, the magnetic specific heat data at low $T$ reveal a significant $T$-linear contribution plus a quadratic $T$ dependence, which may indicate the gapless Dirac QSL phenomenology of the spinon excitations with a linear dispersion.

Recent discoveries of magnetic long-range orders in the icosahedral quasicrystal and topological magnetic structures on the icosahedron (IC) as the hedgehog state and the antihedgehog state have attracted great interest. Here, we report our theoretical analysis of the dynamical as well as static structure of the hedgehog-antihedgehog order in the 1/1 approximant crystal (AC). By constructing the effective magnetic model for the rare-earth-based AC, on the basis of the linear spin-wave theory, the excitation energy is shown to exhibit the reciprocal dispersion, as a consequence of preservation of the spatial inversion symmetry by the hedgehog-antihedgehog ordering. The static structure factor is shown to be expressed generally in the convolution form of the lattice structure factor and the magnetic structure factor on the IC(s) and the numerical calculation reveals the extinction rule. The dynamical structure factor shows that the high intensities appear in the low-energy branch along the $\mathrm{\Gamma }$-X line and the R-$\mathrm{\Gamma }$-M line in the reciprocal space.

Tuning magnetic properties in layered magnets is an important route to realize novel phenomenon related to two-dimensional (2D) magnetism. Recently, tuning antiferromagnetic (AFM) properties through substitution and intercalation techniques has been widely studied in $M\mathrm{P}{X}_3$ compounds. Interesting phenomena, such as diverse AFM structures and even the signatures of ferrimagnetism, have been reported. However, long-range ferromagnetic (FM) ordering has remained elusive. In this work, we explored the magnetic properties of the Cr-substituted $\mathrm{NiP}{\mathrm{S}}_3$. We found that Cr substitution is extremely efficient in controlling spin orientation in $\mathrm{NiP}{\mathrm{S}}_3$. Our study reveals a field-induced spin polarization in lightly (9%) Cr-substituted $\mathrm{NiP}{\mathrm{S}}_3$, which is likely attributed to the attenuation of AFM interactions and magnetic anisotropy due to Cr doping. Our work provides a possible strategy to achieve FM phase in AFM $M\mathrm{P}{X}_3$, which could be useful for investigating 2D magnetism as well as potential device applications.

The realization of perpendicular magnetic anisotropy (PMA) in a rare-earth iron garnet composition has the potential to open up the field of spintronics and magnonics. In this study, we introduce ${\mathrm{Yb}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YbIG) as an iron garnet thin film candidate exhibiting PMA. We have grown highly epitaxial YbIG films on (111) oriented ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ (GGG) substrates. Detailed growth, structural, magnetic, and dynamical properties of the YbIG/GGG(111) thin films are reported. We reveal a transition from the in-plane (IP) to out-of-plane (OOP) magnetic easy-axis as the film thickness decreases. The gradual increase in the OOP anisotropy field from 18 Oe to 1100 Oe with decreasing film thickness is consistent with the observed variation of the OOP lattice parameter due to epitaxial strain. Further, sixfold symmetry in the IP angular variation of resonance field ${\mathrm{H}}_r$ reveals the presence of a significant contribution of the second-order magnetocrystalline anisotropy (${\mathrm{K}}_2$). The damping factor $\alpha \sim {10}^{-2}$ is comparable to TmIG, which has been proposed as a promising material for application due to PMA. These findings present YbIG as a potential contender for spintronic and magnonic applications because of its PMA with moderate $\alpha$.

We have performed electrochemical treatment of the van der Waals antiferromagnetic materials ${\mathrm{FePS}}_3$ and ${\mathrm{NiPS}}_3$ with the ionic liquid $\mathrm{EMIM}\text{−}{\mathrm{BF}}_4$, achieving significant molecular intercalation. Mass analysis of the intercalated compounds, ${\mathrm{EMIM}}_x\text{−}{\mathrm{FePS}}_3$ and ${\mathrm{EMIM}}_x\text{−}{\mathrm{NiPS}}_3$, indicated respective intercalation levels, $x$, of approximately 27% and 37%, and x-ray diffraction measurements demonstrated a massive (over 50%) enhancement of the $c$-axis lattice parameters. To investigate the consequences of these changes for the magnetic properties, we performed magnetic susceptibility and ${}^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) studies of both systems. For ${\mathrm{EMIM}}_x\text{−}{\mathrm{FePS}}_3$, intercalation reduces the magnetic ordering temperature from $T_N=120$ to 78 K, and we find a spin gap in the antiferromagnetic phase that drops from 45 to 30 K. For ${\mathrm{EMIM}}_x\text{−}{\mathrm{NiPS}}_3$, the ordering temperature is almost unaffected (changing from 148 to 145 K), but a change towards nearly isotropic spin fluctuations suggests an alteration of the magnetic Hamiltonian. Such relatively modest changes, given that the huge extension of the $c$ axes is expected to cause a very strong suppression any interlayer interactions, point to the conclusion that the magnetic properties of both parent compounds are determined almost exclusively by two-dimensional (2D), intralayer physics. The changes in transition temperatures and low-temperature spin dynamics in both compounds therefore indicate that intercalation also results in a significant modulation of the intralayer magnetic interactions, which we propose is due to charge doping and localization on the P sites. Our study offers chemical intercalation with ionic liquids as an effective method to control not only the interlayer but also the intralayer interactions in quasi-2D magnetic materials.

Antiferromagnets are promising candidates as active components in spintronic applications. They share features with ferrimagnets in that opposing spin orientations exist in two or more sublattices. Spin-transfer torque and spin pumping are essential ingredients in antiferromagnetic and ferrimagnet spintronics. This paper develops an out-of-equilibrium quantum theory of the spin dynamics of collinear magnets containing many spins coupled to normal metal reservoirs. At equilibrium, the spins are parallel or antiparallel to the easy axis. The theory, therefore, covers collinear antiferromagnets and ferrimagnets. We focus on the resulting semiclassical spin dynamics. The dissipation in the spin dynamics is enhanced due to spin pumping. Spin accumulations in the normal metals induce deterministic spin-transfer torques on the magnet. Additionally, each electron's discrete spin angular momentum causes stochastic fluctuating torques on the antiferromagnet or ferrimagnet. We derive these fluctuating torques. The fluctuation-dissipation theorem holds at high temperatures, including the effects of spin pumping. At low temperatures, we derive shot noise contributions to the fluctuations.

In strongly correlated systems, the complete determination of the dynamical susceptibility $\chi (\mathbf{q},\omega )$ is of special relevance because of the entwinement of the spin and charge components. Although resonant inelastic x-ray scattering (RIXS) spectra are directly related to both the charge $\left[{\chi }_c^{\prime \prime }(\mathbf{q},\omega )\right]$ and the spin $\left[{\chi }_s^{\prime \prime }(\mathbf{q},\omega )\right]$ contributions, only the latter has been extensively studied with RIXS so far. Here we show how to extract from RIXS spectra of high-$T_c$ superconducting cuprates relevant properties of ${\chi }_c^{\prime \prime }$, such as the presence of the superconducting gap and of the pseudogap. In particular, we exploit the temperature dependence of the Cu $L_3$ edge RIXS spectra of underdoped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ at specific wave vectors q. The signature of the two gaps is given by the departure of the low-energy excitation continuum from the Bosonic thermal evolution. This approach can be immediately used to investigate systematically the nature of the pseudogap in cuprates, thereby taking advantage of the RIXS technique that does not suffer the limitations of surface-sensitive electron spectroscopies. Its extension to other interesting materials is foreseen.

We implement the temperature flow scheme first proposed by Honerkamp and Salmhofer [Phys. Rev. B 64, 184516 (2001)] into the pseudo-Majorana functional renormalization group method for quantum spin systems. Since the renormalization group parameter in this approach is a physical quantity, the temperature $T$, the numerical efficiency increases significantly compared to more conventional renormalization group parameters, especially when computing finite-temperature phase diagrams. We first apply this method to determine the finite-temperature phase diagram of the $J_1\text{−}{J}_2$ Heisenberg model on the simple cubic lattice, where our findings support claims of a vanishingly small nonmagnetic phase around the high frustration point $J_2=0.25J_1$. Perhaps most importantly, we find the temperature flow scheme to be advantageous in detecting finite-temperature phase transitions as, by construction, a phase transition is never encountered at an artificial, unphysical cutoff parameter. Finally, we apply the temperature flow scheme to the dipolar XXZ model on the square lattice, where we find a rich phase diagram with a large nonmagnetic regime down to the lowest accessible temperatures. Wherever a comparison with error-controlled (quantum) Monte Carlo methods is applicable, we find excellent quantitative agreement with less than $5\%$ deviation from the numerically exact results.

Non-Fermi liquids arise when strong interactions destroy stable fermionic quasiparticles. The simplest models featuring this phenomenon involve a Fermi surface coupled to fluctuating gapless bosonic order parameter fields, broadly referred to as “Hertz-Millis” models. We revisit a controlled approach to Hertz-Millis models that combines an expansion in the inverse number $\left(N\right)$ of fermion species with an expansion in the deviation of the boson dynamical critical exponent $z$ from 2. The structure of the expansion is found to be qualitatively different in the quantum critical regime $\mathrm{\Omega }\ll q$ and in the transport regime $\mathrm{\Omega }\gg q$. In particular, correlation functions in the transport regime involve infinitely many diagrams at each order in perturbation theory. We provide an explicit and tractable recipe to classify and resum these diagrams. For the simplest Hertz-Millis models, we show that this recipe is consistent with nonperturbative anomaly arguments and correctly captures the fixed point optical conductivity as well as leading corrections from irrelevant operators. We comment on potential applications of this expansion to transport in more complicated Hertz-Millis models as well as certain beyond-Landau metallic quantum critical points.

The Zhang-Rice (ZR) state is a strongly hybridized bound state formed by transition-metal and oxygen atoms. The spin fluctuations within the ZR state are known to play an important role in high-$T_{\mathrm{c}}$ superconductivity in cuprates. Here, we employ a combination of angle-resolved photoemission spectroscopy (ARPES), x-ray photoemission spectroscopy (XPS), and ab initio embedded dynamical mean-field theory (eDMFT) to investigate the influence of magnetic ordering on the spectral characteristics of the valence band and Mn $2p$ core-level in MnO (001) ultrathin films. Our results demonstrate that a complex spin-selective evolution of Mn $3d-\mathrm{O}2p$ hybridization develops due to the long-range antiferromagnetic (AFM) ordering. This hybridization significantly alters the spectral shape and weight of the ZR state. Specifically, in the AFM phase, we observed the sharpening of the ZR state and band folding with the periodicity of the AFM unit cell of MnO(001). We also demonstrated a strong connection between the spectral evolution of the ZR state and the non-local screening channels of the photoexcited core holes. Further, our detailed temperature-dependent study reveals the presence of short-range antiferromagnetic correlations that exist at much higher temperatures than Neel temperature $\left(T_{\mathrm{N}}\right)$ and shows the evolution of the ZR state across the magnetic transitions and its implication to the core-hole screening in $3d$ binary transition metal oxides.

We investigate the magnetic order and related strongly correlated effects in a one-dimensional Ising-Kondo lattice with transverse field. This model is the anisotropic limit of the conventional isotropic Kondo lattice model, in the sense that the itinerant electrons interact with the localized magnetic moments via only longitudinal Kondo exchange. Adopting the numerical density-matrix renormalization group method, we map out the ground-state phase diagram in various parameter spaces. Depending on the Kondo coupling and filling number, three distinct phases, including a metallic paramagnetic, a metallic ferromagnetic, and a gapped spin-density wave phase, are obtained. The spin-density wave is characterized by an ordering wave vector, which coincides with the nesting wave vector of the Fermi surface. This makes the corresponding magnetic transition a spin analog of the Peierls transition occurring in the one-dimensional metal. Moreover, by analyzing the momentum distribution function and charge correlation function, the conduction electrons are shown to behave like free spinless fermions in the ferromagnetic phase. We finally discuss the effect of the repulsive Hubbard interaction between conduction electrons. Our paper enriches the Kondo physics and deepens the current understanding of the heavy fermion compounds.

A double-layer heterostructure is a manifestly bipartite system. Once the electron gases from both layers are coupled, the system is described by a global quantum wave function, which reflects all discrete degrees of freedom of the system, including layer, band, spin, etc. Because of the interlayer coupling these degrees of freedom should be entangled, i.e., the global wave function cannot be described as a simple tensor product of wave functions on each of the subspaces. Here we study the entanglement between such discrete degrees of freedom as layers and spectral bands in a particular double-layer system, in which Dirac electron gases populating each layer engage in an interlayer pairing similar to superconductivity. We show that the entanglement entropy is a function of the pairing order parameter and reflects the composition of the band structure or density of states, exhibiting specific reaction features for saddle points or van Hove singularities. This makes it possible to vary the entanglement degree by manipulations as simple as the change of temperature. We argue that the diagnosis for the system to reside in that entangled state can be made with the help of simple correlation functions, e.g., the density-density correlator measured in one of the layers. Once its measurement provides for a finite result, the system is entangled.

Chiral magnets with Dzyaloshinskii-Moriya interactions feature a rich phase diagram with a variety of thermodynamical phases. These include helical and conical spin arrangements and topologically charged objects such as (anti)Skyrmions. Crucially, due to hysteresis effects, the thermodynamical phases can coexist at any given temperature and external magnetic field, typically leading to metastability of, e.g., the material's topological phase. In this paper, we use Monte Carlo simulations to study these effects. We compute the relative free energies of coexisting states, enabling us to determine the ground state at all values of the external parameters. We also introduce a method to estimate the activation energy, i.e., the height of the energy barrier that separates the topological phase from the ground state. This is one of the key ingredients for the determination of the Skyrmion lifetime, which is relevant for technological applications. Finally, we prescribe predicting the system's evolution through any path in the space of external parameters. This can serve as a guideline to prepare the magnetic material in any desired phase or even trigger a phase transition in an experimental setup.

The layered compound ${\mathrm{Mg}}_3{\mathrm{Sb}}_2$ displays remarkable thermoelectric properties at low to moderate temperatures due to its low lattice thermal conductivity, akin to heavier materials like SnSe, PbTe, or ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. However, the underlying cause of this low lattice thermal conductivity in the lightweight ${\mathrm{Mg}}_3{\mathrm{Sb}}_2$ remains unclear. Employing temperature-dependent Raman spectroscopy, we have identified the existence of a robust anharmonic interaction between the optical phonon modes in polycrystalline ${\mathrm{Mg}}_3{\mathrm{Sb}}_2$. Additionally, we have observed a gradual decay of all optical phonons as temperature increases confirming the decrease in lattice thermal conductivity at higher temperatures. The introduction of Li into ${\mathrm{Mg}}_3{\mathrm{Sb}}_2$ lattice results in a disparity among the crystallographic axes for the phonon modes, intensifying the anharmonic phonon vibrations in ${\mathrm{Mg}}_{2.985}{\mathrm{Li}}_{0.015}{\mathrm{Sb}}_2$ compared to undoped ${\mathrm{Mg}}_3{\mathrm{Sb}}_2$. The estimated anharmonic constant $\sim 4.5\times {10}^{-4}{\mathrm{K}}^{-1}$ for ${\mathrm{Mg}}_{2.985}{\mathrm{Li}}_{0.015}{\mathrm{Sb}}_2$ closely resembles those of other heavier thermoelectric systems, mainly attributed to quasiharmonic volume expansion and anharmonic phonon-phonon interaction. The lattice thermal conductivity estimated from the Raman modes aligns with experimentally measured values, confirming the significant influence of optical phonons on the thermal transport of layered ${\mathrm{Mg}}_3{\mathrm{Sb}}_2$. These findings offer a comprehensive exploration of the interplay between optical phonon modes and the origins of substantial phonon anharmonicity in the lightweight polycrystalline ${\mathrm{Mg}}_3{\mathrm{Sb}}_2$ system.

Spin photogalvanic effect is a nonlinear effect that can generate spin currents through optical excitation in intrinsic semiconductors without parity inversion symmetry. The efficient control of the spin photogalvanic effect is of great significance for the research of computing-in-memory devices. In this work, we investigate the ferroelectric modulation of the spin photogalvanic effect in two-dimensional (2D) van der Waals (vdW) ferroelectric semiconductors with spin-orbit coupling, including the in-plane, out-of-plane, and in-plane/out-of-plane-coupled ferroelectrics. We provide the general form of the spin photogalvanic effect controlled by ferroelectricity in 2D vdW spin-orbit coupling ferroelectric semiconductors by the second-order perturbation theory. In the in-plane ferroelectrics excited by circularly polarized light, we discover an effect where the reversal of the ferroelectric polarization will maintain the spin current unchanged but change the direction of the charge current. We name this effect the hidden spin current modulation. Using first-principles quantum transport simulation, we validate our theory with three cases of the black phosphorus-like Bi (in-plane ferroelectric), monolayer α-GeTe (out-of-plane ferroelectric), and $\alpha \text{−}\mathrm{I}{\mathrm{n}}_2\mathrm{S}{\mathrm{e}}_3$ (in-plane and out-of-plane coupled ferroelectric). Our study paves the way for the research of next-generation low-dimensional computing-in-memory devices.

Nonequilibrium quantum noise $S^{>}(\omega ,V)$ measured at finite frequencies $\omega$ and bias voltages $V$ probes Majorana bound states in a host nanostructure via fluctuation fingerprints unavailable in average currents or static shot noise. When Majorana interference is brought into play, it enriches nonequilibrium states and makes their nature even more unique. Here we demonstrate that an interference of two Majorana modes via a nonequilibrium quantum dot gives rise to a remarkable finite frequency response of the differential quantum noise $\partial S^{>}(\omega ,V,\mathrm{\Delta }\varphi )/\partial V$ driven by the Majorana phase difference $\mathrm{\Delta }\varphi$. Specifically, at low bias voltages there develops a narrow resonance of width $\hslash \mathrm{\Delta }\omega \sim {sin}^2\mathrm{\Delta }\varphi$ at a finite frequency determined by $V$, whereas for high bias voltages there arise two antiresonances at two finite frequencies controlled by both $V$ and $\mathrm{\Delta }\varphi$. We show that the maximum and minimum of these resonance and antiresonances have universal fractional values, $3e^3/4h$ and $-e^3/4h$. Moreover, detecting the frequencies of the antiresonances provides a potential tool to measure $\mathrm{\Delta }\varphi$ in nonequilibrium experiments on Majorana finite frequency quantum noise.

Vacuum fluctuations are a fundamental and irremovable property of a quantized electromagnetic field. These fluctuations are the cause of the Casimir effect—mutual attraction of two electrically neutral metallic plates in vacuum in the absence of any other interactions. For most geometries and materials, the Casimir effect is strictly attractive, leading to the only stable equilibrium configuration with merged plates. Recent observation showed, however, that this unavoidable vacuum-induced attraction can be mitigated by the presence of electrostatic repulsion produced by the formation of double electric layers, and a stable equilibrium between two charged metallic plates in a solution of an organic salt can be reached Munkhbat et al., Nature (London) 597, 214 (2021). Here, we study theoretically in detail equilibrium configurations and their dynamical behavior in the system of two parallel metallic films coupled by the Casimir and electrostatic interactions. We analyze the effect of various parameters of the system—such as the salt concentration and temperature—on the equilibrium cavity thicknesses, inspect resonant properties of the resulting optomechanical system near equilibrium, and examine its stochastic dynamics under thermal fluctuations of the environment.