We consider photons strongly coupled to the excitonic excitations of a coupled quantum well, in the presence of an electric field. We show how, under a field increase, the hybrid polariton made of a photon coupled to hybrid carriers lying in the two wells transforms into a dipolariton made of a photon coupled to direct and indirect excitons. We also show how the cavity photon lifetime and the coherence time of the carrier wave vectors that we analytically handle through non-hermitian Hamiltonians affect these polaritonic states. While the hybrid polaritons display a spectral singularity where the eigenvalues coalesce, known as an exceptional point, that depends on detuning and lifetimes, we find that the three dipolaritonic states display an anticrossing without exceptional point due to the interaction between photons, direct, and indirect excitons.

We study gate field effects on the heterostructure ${\mathrm{Mn}}_{12}{\mathrm{O}}_{12}{\left(\mathrm{COOH}\right)}_{16}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4\left|\mathrm{graphene}\right|\mathrm{GaAs}$ via first-principles calculations. We find that under moderate doping levels, electrons can be added to but not taken from the single-molecule magnet ${\mathrm{Mn}}_{12}{\mathrm{O}}_{12}{\left(\mathrm{COOH}\right)}_{16}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4$ (${\mathrm{Mn}}_{12}$). The magnetic anisotropy energy (MAE) of ${\mathrm{Mn}}_{12}$ decreases as the electron-doping level increases due to electron transfer from graphene to ${\mathrm{Mn}}_{12}$ and change in the band alignment between ${\mathrm{Mn}}_{12}$ and graphene. At an electron-doping level of $-5.00\times {10}^{13}\text{cm}{}^{-2}$, the MAE decreases by about 18% compared with zero doping. The band alignment between graphene and GaAs is more sensitive to electron doping than to hole doping, since the valence band of GaAs is close to the Fermi level. The GaAs substrate induces a small band gap in the supported graphene under zero gate field and a nearly strain-free configuration. Finally, we propose a vertical tunnel junction for probing the gate dependence of MAE via electron transport measurements.

Paramagnetic materials exhibit a unique thermoelectric effect near the ferromagnetic transition point due to spin fluctuations. This phenomenon is referred to as paramagnon drag. In this study, we calculate the contribution of this paramagnon drag to the Seebeck coefficient microscopically based on the linear response theory. Consequently, we obtain a general formula for the contribution to the Seebeck coefficient due to the paramagnon drag and then clarify the conditions in which the Seebeck coefficient is enhanced near the ferromagnetic transition point for a single-band and isotropic system. Moreover, we calculate the Seebeck coefficients for a mixture of free-electron-like and flat bands.

Compounds with kagome lattice usually host many exotic quantum states, including the quantum spin liquid, non-trivial topological Dirac bands and a strongly renormalized flat band, etc. Recently an interesting vanadium based kagome family $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A=\mathrm{K},\mathrm{Rb},\text{or}\mathrm{Cs})$ was discovered, and these materials exhibit multiple interesting properties, including unconventional saddle-point driving charge density wave (CDW) state, superconductivity, etc. Furthermore, some experiments show the anomalous Hall effect which inspires us to believe that there might be some chiral flux current states. Here we report scanning tunneling measurements by using spin-polarized tips. Although we have observed clearly the $2a_0\times 2a_0$ CDW and $4a_0$ stripe orders, the well-designed experiments with refined spin-polarized tips do not reveal any trace of the chiral flux current phase in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ within the limits of experimental accuracy. No observation of the local magnetic moment in our experiments may put an upper bound constraint on the magnitude of magnetic moments induced by the possible chiral loop current which has a time-reversal symmetry breaking along $c$ axis in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$.

High-quality single crystals of EuAuAs were studied by means of powder x-ray diffraction, magnetization, magnetic susceptibility, heat capacity, electrical resistivity and magnetoresistance measurements. The compound crystallizes with a hexagonal structure of the ZrSiBe type (space group $P{6}_3/mmc$). It orders antiferromagnetically below 6 K due to the magnetic moments of divalent Eu ions. The electrical resistivity exhibits metallic behavior down to 40 K, followed by a sharp increase at low temperatures. The magnetotransport isotherms show a distinct metamagneticlike transition in concert with the magnetization data. The antiferromagnetic ground state in EuAuAs was corroborated in the ab initio electronic band structure calculations. Most remarkably, the calculations revealed the presence of nodal line without spin-orbit coupling and Dirac point with inclusion of spin-orbit coupling. The $Z{}_2$ invariants under the effective time reversal and inversion symmetries make this system nontrivial topological material. Our findings, combined with experimental analysis, makes EuAuAs a plausible candidate for an antiferromagnetic topological nodal-line semimetal.

We investigate the disorder-driven phase transitions in bosonic fractional quantum Hall liquids at filling factors $f=1/2$ and $f=1$ in the lowest Landau level. We use the evolution of ground-state entanglement entropy, fidelity susceptibility, and Hall conductance with increasing disorder strength to identify the underlying phase transitions. The critical disorder strengths obtained from these different quantities are consistent with each other, validating the reliability of our numerical calculations based on exact diagonalization. At $f=1/2$, we observe a clear transition from the bosonic Laughlin state to a trivial insulating phase. At $f=1$, we identify a direct phase transition from the non-Abelian bosonic Moore-Read state to a trivial insulating phase, although some signs of a disorder-induced intermediate fractional quantum Hall phase were recently reported for the $f=5/2$ fermionic cousin.

We study the nonequilibrium quench dynamics of a mixed Sachdev-Ye-Kitaev model, with competing two-body random interactions leading to maximally chaotic non-Fermi liquid dynamics and a single body term which dominates at low temperatures and leads to Fermi liquid behavior. For different quench protocols, including sudden switching of two-body interaction and double quench protocols, we solve the large $N$ real-time Dyson equation on the Keldysh contour and compute the dynamics of Green's functions from which we obtain effective temperature and relaxation rates. We show that the model thermalizes to a finite temperature equilibrium and that depending on the value of the quench parameters, the effective temperature can be below or above the Fermi-liquid to non-Fermi liquid crossover scale, which can then be accessed through the nonequilibrium dynamics. We identify quench protocols for which the heating dynamics slow down significantly—an effect that we interpret as a signature of prethermalization.

The spin photocurrents, direct currents induced by light, hold great promise for introducing new elements to spintronics. However, a general theory for spin photocurrents in real materials which is applicable to systems with spin-orbit coupling or noncollinear magnetism is absent. Here, we develop such a general theory of second-order spin photocurrents. We find that the second-order spin photocurrents can be classified into Drude, Berry curvature dipole, shift, injection, and rectification currents, which have different physical origins and symmetry properties. Surprisingly, our theory predicts a direct pure spin rectification current in an insulator induced by photons with energies lower than the material band gap. This phenomenon is absent in the case of the charge photocurrent. We find that the pure spin current of BiTeI induced by subgap light is large enough to be observable in experiments. Moreover, the subgap pure spin photocurrent is highly tunable with the polarization of light and the flowing direction of the spin photocurrent. This study lays the groundwork for the study of nonlinear spin photocurrents in real materials and provides a route to engineer light-controlled spin currents.

We propose a “Floquet engineering” formalism to systematically design a periodic driving protocol in order to stroboscopically realize the desired system starting from a given static Hamiltonian. The formalism is applicable to interacting and noninteracting quantum systems which have an underlying closed Lie algebraic structure. Unlike previous attempts at Floquet engineering, our method produces the desired Floquet Hamiltonian at any driving frequency and is not restricted to the fast or slow driving regimes. The approach is based on Wei-Norman ansatz, which was originally proposed to construct a time-evolution operator for any arbitrary driving. Here, we apply this ansatz to the micromotion dynamics, defined within one period of the driving, and engineer the functional form and operators of the driving protocol by fixing the gauge of the micromotion. To illustrate our idea, we use a two-band system or the systems consisting of two sublattices as a testbed. Particularly, we focus on engineering the cross-stitched lattice model that has been a paradigmatic flat-band model.

The indirect quartic interaction of spins is suggested to play an important role in two-dimensional magnets with trigonal prismatic symmetry such as an ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ monolayer and many transition metal dichalcogenides. The proposed interaction is described by terms in micromagnetic energy that are linear in magnetization gradients. Such terms enable the stability of noncollinear magnetic textures. We investigate signatures of the quartic interaction in magnon spectra in the presence of anisotropy and an external magnetic field. We also show how magnetic spirals, which are induced by the proposed interaction, can be manipulated by an external field. Our analysis is based on symmetry considerations and can be used to quantify the quartic interaction strength in experiments with magnetic monolayers.

The realization of fourfold anisotropic magnetoresistance (AMR) in $3d-5d$ heterostructures has boosted major efforts in antiferromagnetic (AFM) spintronics. However, despite the potential of incorporating strong spin-orbit coupling, only small AMR signals have been detected thus far, prompting a search for mechanisms to enhance the signal. In this paper, we demonstrate an extraordinarily elevated fourfold AMR of 70% realized in $\mathrm{CaMn}{\mathrm{O}}_3/\mathrm{CaIr}{\mathrm{O}}_3$ thin film superlattices. We find that the biaxial magnetic anisotropy and the spin-flop transition in a nearly Mott insulating phase form a potent combination, each contributing one order of magnitude to the total signal. Dynamics between these phenomena capture a subtle interaction of pseudospin coupling with the lattice and external magnetic field, an emergent phenomenon creating opportunities to harness its potential in AFM spintronics.

Here, we study the surface electronic structure of $1T\text{−}\mathrm{V}{\mathrm{Se}}_2$ by means of angle-resolved photoemission spectroscopy and uncover a dispersionless emission located in the vicinity of the Fermi level. Its crystal momentum dependency reveals that it occupies large portions of the Brillouin zone, where no bulk band is expected. Upon electron doping (deposition of Rb atoms), the system evolves in a surprising way. Besides the expected down-shifting of the bands, a splitting of both bulk and dispersionless emission is observed. This peculiar behavior strongly suggests the intrinsic nature of the dispersionless emission. Its characterization may therefore be relevant to a deeper understanding of the physics of transition metal dichalcogenides.

The “states-non-conserving” fermion density of states (DOS), deduced from the specific heat of hole-doped cuprates, could arise from a Kondo or heavy fermionlike DOS being suppressed by antiferromagnetic spin fluctuations. The large Fermi surface predicted by band theory and observed experimentally is still expected for zero pseudogap but with an effective mass corresponding to a Kondo temperature $T_K\simeq 800\mathrm{K}$. A finite pseudogap could divide it into Fermi arcs. Theoretical results for the asymmetric Anderson model can account for the experimental Wilson ratio.

The elastic properties of a series of Ge-Se glasses are measured during irradiation with sub-band-gap light using a laser-induced transient grating method. The elastic modulus is found to decrease prominently with increasing irradiation intensity. The process is found to be less prominent in glasses of high average coordination $\langle r\rangle$. Measured kinetics in the millisecond range are found to be too slow for a photoinduced electronic process and instead suggest a thermal origin. Infrared thermography is performed during irradiation to monitor temperature changes during photodarkening, photoexpansion, and photoelastic measurements. It is found that in the conditions of irradiation where photoelasticity is observed, all photostructural changes are directly associated with a change in temperature. comsol modeling of thermal flow through the sample closely reproduces the kinetics of photodarkening. Transient grating measurements as a function of temperature confirm that the change in elasticity during irradiation is essentially a thermally induced process. Currently available experimental evidence indicates that the photoelastic phenomena are not an optoelectronic process but rather the result of laser heating.

We present here a study of the magnetic properties of the antiferromagnetic dimer material ${\mathrm{CuVOF}}_4{\left({\mathrm{H}}_2\mathrm{O}\right)}_6·{\mathrm{H}}_2\mathrm{O}$, in which the dimer unit is composed of two different $S=1/2$ species, Cu(II) and V(IV). An applied magnetic field of ${\mu }_0{H}_{\mathrm{c}1}=13.1\left(1\right)$ T is found to close the singlet-triplet energy gap, the magnitude of which is governed by the antiferromagnetic intradimer $J_0\approx 21$ K, and interdimer $J^{\prime }\approx 1$ K, exchange energies, determined from magnetometry and electron-spin resonance measurements. The results of density functional theory (DFT) calculations are consistent with the experimental results. The DFT calculations predict antiferromagnetic coupling along all nearest-neighbor bonds, with the magnetic ground state comprising spins of different species aligning antiparallel to one another, while spins of the same species are aligned parallel. The magnetism in this system cannot be accurately described by the overlap between localized V orbitals and magnetic Cu orbitals lying in the Jahn-Teller (JT) plane, with a tight-binding model based on such a set of orbitals incorrectly predicting that interdimer exchange should be dominant. DFT calculations indicate significant spin density on the bridging oxide, suggesting instead an unusual mechanism in which intradimer exchange is mediated through the O atom on the Cu(II) JT axis.

Josephson junctions (JJs), where both time-reversal and inversion symmetry are broken, exhibit a phase shift ${\phi }_0$ in their current-phase relation. This allows for an anomalous supercurrent to flow in the junction even in the absence of a phase bias between the superconductors. We show that a finite phase shift also manifests in the so-called Andreev interferometers—a device that consists of a mesoscopic conductor coupled to the ${\phi }_0$ junction. Due to the proximity effect, the resistance of this conductor is phase sensitive—it oscillates by varying the phase of the JJ. As a result, the quasiparticle current $I_{\mathrm{qp}}$ flowing through the conductor has an anomalous component, which exists only at finite ${\phi }_0$. Thus, the Andreev interferometry could be used to probe the ${\phi }_0$ effect. We consider two realizations of the ${\phi }_0$ junction and calculate $I_{\mathrm{qp}}$ in the interferometer: a superconducting structure with spin-orbit coupling and a system of spin-split superconductors with spin-polarized tunneling barriers.

Broadband coherent anti-Stokes Raman scattering (B-CARS) has emerged in recent years as a promising chemosensitive high-speed imaging technique. B-CARS allows for the detection of vibrational sample properties in analogy to spontaneous Raman spectroscopy, but also makes electronic sample environments accessible due to its resonant excitation mechanism. Nevertheless, this technique has only gained interest in the biomedical field so far, whereas CARS investigations on solid-state materials are rare and concentrate on layered, two-dimensional materials such as graphene and hexagonal boron nitride . In this work, we discuss the specific properties of this technique when applied to single-crystalline samples, with respect to signal generation, phase matching, and selection rules in the model systems lithium niobate and lithium tantalate. Via polarized B-CARS measurements and subsequent phase retrieval, we validate the predicted selection rules, unequivocally assign the phonons of the ${\mathrm{A}}_1$(TO), E(TO) and ${\mathrm{A}}_1$(LO) branches to the detected CARS peaks, and address differences in spontaneous Raman spectroscopy concerning peak frequencies and scattering efficiencies. We thus establish this technique for future investigations of solid-state materials, specifically in the field of ferroelectric single crystals.

Single crystals of the frustrated $S=1/2$ ferro-antiferromagnetic proximate square lattice material ${\mathrm{SrZnVO}\left({\mathrm{PO}}_4\right)}_2$ are studied in magnetometric, calorimetric, neutron diffraction, and inelastic neutron scattering experiments. The measured spin wave spectrum reveals a substantial degree of magnetic frustration and a large quantum renormalization of the exchange constants. The $H\text{−}T$ magnetic phase diagram is established. It features a novel presaturation phase, which appears for only one particular field orientation. The results are discussed noting the similarities and differences with the previously studied and similarly structured ${\mathrm{Pb}}_2\mathrm{VO}({\mathrm{PO}}_4{)}_2$ compound.

An emergent $\mathrm{SU}\left(4\right)$ symmetry discovered in the microscopic model for $d^1$ honeycomb materials [M. G. Yamada, M. Oshikawa, and G. Jackeli, Phys. Rev. Lett. 121, 097201 (2018)] has enabled us to tailor exotic $\mathrm{SU}\left(4\right)$ models in real materials. In the honeycomb structure, the emergent $\mathrm{SU}\left(4\right)$ Heisenberg model would potentially have a quantum spin-orbital liquid ground state due to the multicomponent frustration, and we can also expect similar spin-orbital liquids in three-dimensional versions of the honeycomb lattice. In such quantum spin-orbital liquids, both the spin and orbital degrees of freedom become fractionalized and entangled together due to the strong frustrated interactions between them. Similarly to spinons in pure quantum spin liquids, quantum spin-orbital liquids can host not only spinon excitations, but also fermionic orbitalon excitations at low temperature.

We study the phase dynamics, IV characteristics, and magnetization dynamics of the ${\phi }_0$ Josephson junction at small values of spin-orbit interaction, ratio of the Josephson junction to magnetic energy, and Gilbert damping. We demonstrate that the coupled Landau-Lifshitz-Gilbert-Josephson dynamics is reduced to a scalar nonlinear Duffing oscillator. The resulting Duffing equation incorporates the Gilbert damping in a special way across the dissipative term and the restoring force. An anomalous shift of the ferromagnetic resonance frequency with decreasing Gilbert damping is found. We demonstrate that there is a critical damping value at which nonlinearity comes into play, and it changes the damping dependence of the ferromagnetic resonance.