We study a model of noninteracting spinless fermions coupled to local dephasing and boundary drive and described within a Lindblad master equation. The model features an interplay between infinite temperature thermalization due to bulk dephasing and a nonequilibrium stationary state due to the boundary drive and dissipation. We revisit the linear and nonlinear transport properties of the model, featuring a crossover from ballistic to diffusive scaling, and compute the spectral and occupation properties encoded in the single-particle Green's functions, that we compute exactly using the Lindblad equations of motion in spite of the interacting nature of the dephasing term. We show that the distribution function in the bulk of the system becomes frequency independent and flat, consistent with infinite temperature thermalization, while near the boundaries it retains strong nonequilibrium features that reflect the continuous injection and depletion of particles due to driving and dissipation.

The linear magnetoelectric effect and multiferroicity phenomena occur independently due to breaking inversion symmetry below the magnetically ordered state of either transition metal or rare-earth ions. Here, we report the occurrence of a linear magnetoelectric effect and magnetic field-induced ferromagnetism and ferroelectricity below $T_{\mathrm{N}}^R$ in the orthorhombic green phases $R_2\mathrm{BaCu}{\mathrm{O}}_5$ ($R=\mathrm{Dy}$ and Ho). They undergo a long-range antiferromagnetic ordering of ${\mathrm{Cu}}^{2+}$ ($T_{\mathrm{N}}^{\mathrm{Cu}}=18.5$ and 17.5 K) and $R^{3+}$ ions ($T_{\mathrm{N}}^{\mathrm{Dy}}=10.7\mathrm{K}$ and $T_{\mathrm{N}}^{\mathrm{Ho}}=8\mathrm{K}$). The neutron diffraction study reveals that these compounds undergo a first-order magnetic transition from the high-temperature centrosymmetric antiferromagnetic phase ($P_{\mathrm{b}}{112}_1/n$) to the low-temperature noncentrosymmetric phases $Pn{m}^{\prime }a$ (Dy) and $P{112}_1^{\prime }/a$ (Ho), which allow linear magnetoelectric coupling. This is consistent with field-induced electric polarization, below $T_{\mathrm{N}}^R$, which varies linearly up to ∼1.2 T. Above a critical field $\left(H_{\mathrm{c}}>1.2\mathrm{T}\right)$, both compounds exhibit metamagnetic transitions with magnetization close to the saturation value $M_s \sim 10.1{\mu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ (Dy) and $\sim 11.8{\mu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ (Ho) at 7 T. Above the metamagnetic transition, a new polar state appears with large electric polarization, indicating field-induced ferroelectricity. We discuss the important role of $4f\text{−}3d$ coupling in determining the ground state magnetic structure responsible for the magnetoelectric coupling in both compounds.

It is shown that potential barriers in bilayer graphene (BLG) and monolayer transition metal dichalcogenides (TMDs) can split a valley unpolarized incident current into reflected and transmitted currents with opposite valley polarization. Valley asymmetric transmission inevitably occurs because of the low symmetry of the total Hamiltonian and when total external reflection occurs the transmission is 100% valley polarized in BLG and 100% spin and valley polarized in TMDs, except for exponentially small corrections. By adjusting the potential, 100% polarization can be obtained regardless of the crystallographic orientation of the barrier. A valley polarizer can be realized by arranging for a collimated beam of carriers to be incident on a barrier within the range of angles for total external reflection. The transmission coefficients of barriers with a relative rotation of $\pm \pi /3$ are related by symmetry. This allows two barriers to be used to demonstrate that the current is valley polarized. A soft-walled potential is used to model the barrier and the method used to find the transmission coefficients is explained. In the case of monolayer TMDs, a four-band $\mathbf{k}·\mathbf{p}$ Hamiltonian is used and the $\mathbf{k}·\mathbf{p}$ parameters are obtained by fitting to ab initio band structures.

The interplay of symmetry-breaking ordered states, such as superconductivity, charge density waves, magnetism, and pseudogaps, is a fundamental issue in correlated systems. Periodic modulation and antiferromagnetism often coexist in the proximity of phase diagram region in high-$T_c$ superconductors. It is also worth noting that different order states appear in a situation on comparable temperature scales, so these orders are intertwined and competing on the same footing. The magnetism of vdW material ${\mathrm{Fe}}_{5-x}{\mathrm{GeTe}}_2$, with one of the highest reported bulk Curie temperatures, is found to be sensitive to thermal history and external magnetic field. However, the temperature-dependent magnetization with two characteristic points still lacks a unified picture to describe it. Using angle-resolved photoemission spectroscopy, scanning tunneling microscopy, magnetic property measurements, and first-principles calculations, the complex yet intriguing magnetic behaviors are gradually unveiled. A competition mechanism between charge order and ferromagnetism is proposed and firmly observed by experimental measurements. As the ferromagnetic order strengthens at low temperature, the charge order will be suppressed. Exchange splitting in itinerant ferromagnetism plays a significant role in the temperature evolution of band structure and causes a Lifshitz transition, which provides more control means to realize novel devices at room temperature.

We investigate the phase diagram of a two-dimensional driven-dissipative system of polaritons coupled to an excitonic reservoir. We find that two critical points exists. The first corresponds to the quasicondensation and the second to a first-order phase transition from the nonuniform state with spatially modulated density to a uniform state. The latter is related to the modulational instability of a homogeneous state due to the repulsive interactions with the noncondensed reservoir. The first-order character of the transition is evidenced by a discontinuity in the density and the correlation length as well as the phase coexistence and metastability. Moreover, we show that a signature of a Berezinskii-Kosterlitz-Thouless-like transition can be observed in the nonuniform phase.

We conduct a combined experimental and theoretical study of the quantum confined Stark effect in GaAs/AlGaAs quantum dots obtained with the local droplet etching method. In the experiment, we probe the permanent electric dipole and polarizability of neutral and positively charged excitons weakly confined in GaAs quantum dots by measuring their light emission under the influence of a variable electric field applied along the growth direction. Calculations based on the configuration-interaction method show excellent quantitative agreement with the experiment and allow us to elucidate the role of Coulomb interactions among the confined particles and—even more importantly—of electronic correlation effects on the Stark shifts. Moreover, we show how the electric field alters properties such as built-in dipole, binding energy, and heavy-light hole mixing of multiparticle complexes in weakly confining systems, underlining the deficiencies of commonly used models for the quantum confined Stark effect.

Conventional electromagnetic multipoles can be completed by complementary sources of toroidal moments, opening the door to the engineering of nanophotonic devices. The main contribution of this study is comparing different light sources for enhancing the toroidal dipole response in a given system. We theoretically study the toroidal dipole excitation in an individual dielectric nanodisk by structured light illumination, including the tightly focused radially polarized beam and the focused doughnut pulse. The toroidal dipole and anapole can be excited by the interplay of the radial and longitudinal components of the incident light. As opposed to the plane wave illumination, the tightly focused radially polarized light can excite a near-ideal toroidal dipole while the contributions of the Cartesian electric dipole and other modes are significantly suppressed. We also show that the focused doughnut pulse is a promising tool for exciting a resonant toroidal response in nanophotonic systems. Furthermore, it is demonstrated that toroidal-driven field confinement leads to an enhancement of energy concentration inside the nanodisk that can potentially increase light harvesting and boost both linear and nonlinear light-matter interactions.

Profiles of the spin and orbital angular momentum accumulations induced by a longitudinally applied electric field are explored in nanoribbons of $p$-band systems with a honeycomb lattice. We show that nanoribbons with zigzag borders can exhibit orbital magnetoelectric effects. More specifically, we have found that purely orbital magnetization oriented perpendicularly to the ribbon may be induced in these systems by means of the external electric field when sublattice symmetry is broken. The effect is rather general and may occur in other multiorbital materials.

Alternative techniques for probing hyperbolic phonon polaritons (HPPs) in two-dimensional materials will support the development of the emerging technologies in this field. Previous reports have shown that it is possible for $\mathrm{W}{\mathrm{Se}}_2$ monolayers in contact with the hexagonal boron nitride ($h\text{−}\mathrm{BN}$) to generate HPPs in the $h\text{−}\mathrm{BN}$ via Raman scattering. In this paper, we set out our results on HPP Raman scattering induced in $h\text{−}\mathrm{BN}$ by $\mathrm{W}{\mathrm{Se}}_2$ and $\mathrm{Mo}{\mathrm{Se}}_2$ monolayers including multiple resonances at which the Raman scattering is enhanced. Analysis of the observed Raman line shapes demonstrates that Raman scattering allows HPPs with wave vectors with magnitudes significantly in excess of $15000\mathrm{c}{\mathrm{m}}^{–1}$ to be probed. We present evidence that the Raman scattering can probe HPPs with frequencies less than the expected lower bound on the reststrahlen band, suggesting new HPP physics still waits to be discovered.

This paper proposes a hybrid resonant-scattering device combining local resonance and Bragg scattering to achieve simultaneous topological valley-state transport in multiple frequency bands. This acoustic structure was obtained by integrating two types of Helmholtz resonators arranged in a triangular lattice pattern in an air environment. The Dirac point frequency was dominated by the combined strength of resonance and Bragg scattering, presenting a dynamic change process, according to which four designable Dirac points were obtained at frequencies below 14 kHz. Four independently designed and regulated acoustic topological valley transports appeared along the interface separating the topologically diverse sonic crystals after introducing a rotating-scatterer mechanism, as demonstrated by the numerical calculations and experimental results. In addition, since the valley edge states located in the separated edge bands caused by combining resonance and Bragg scattering were interface dependent, a right-hand rule was proposed to evaluate the interface type. This study paves the way for the engineering application of multiband acoustic antennas, acoustic logic control, and other multifunctional acoustic devices.

Dependence of the critical current $I_c$ on the applied magnetic field $H_a$ is theoretically studied for a thin superconducting strip of a rectangular cross section, taking an interplay between the Bean-Livingston and the geometric barriers in the sample into account. It is assumed that bulk vortex pinning is negligible, and the London penetration depth $\lambda$ is essentially less than the thickness $d$ of the strip. To investigate the effect of these barriers on $I_c$ rigorously, a two-dimensional distribution of the current over the cross section of the sample is derived, using the approach based on the methods of conformal mappings. With this distribution, the dependence $I_c\left(H_a\right)$ is calculated for the fields $H_a$ not exceeding the lower critical field. This calculation reveals that the following two situations are possible: (i) The critical current $I_c\left(H_a\right)$ is determined by the Bean-Livingston barrier in the corners of the strip. (ii) The geometrical barrier prevails at low $H_a$, but with increasing magnetic field, the Bean-Livingston barrier begins to dominate. The realization of one or the other of these two situations is determined by the ratio $\lambda /d$.

We determine theoretically the interaction between two magnetic impurities embedded in a spin-split $s$-wave superconductor. The spin-splitting in the superconductor gives rise to two different interaction types between the impurity spins, depending on whether their spins lie in the plane perpendicular to the spin-splitting field (Heisenberg) or not (Ising). For impurity separation distances exceeding ${\xi }_S$, we find that the magnitude of the spin-splitting can determine whether an antiferromagnetic or ferromagnetic alignment of the impurity spins is preferred by the RKKY interaction. Moreover, the Ising and Heisenberg terms of the RKKY interaction alternate on being the dominant term and their magnitudes oscillate as a function of distance between the impurities.

A superconductor can interact with magnets through the magnetic field which is induced by the supercurrent. However, this interaction is rather weak and requires relatively large magnets to reach a sizable hybridization of microwave electromagnetic modes with magnons. The size of the device can be drastically reduced by means of the large interfacial exchange interaction between spins in a magnet and a superconductor. In the spin-orbit coupled superconductor this interaction can be transmitted to the $s$-wave condensate through a mixing of triplet and singlet Cooper pairs. In this paper we theoretically consider thin antiferromagnetic films, which make a spin compensated contact to a superconducting wire, which forms a cavity for Mooij-Schön plasma waves. The effective Lagrangian is derived where the interaction of these waves with magnons is taken into account. Frequencies of hybrid magnon-plasmon modes are calculated. A system of two micromagnets placed far apart are also considered and their mutual coupling through the cavity mode is calculated.

Multiband effects can lead to fundamentally different electronic behavior of solids, as exemplified by the possible emergence of Fermi surfaces of Bogoliubov quasiparticles in centrosymmetric superconductors which break time-reversal symmetry. We extend the analysis of possible pairing symmetries, the corresponding nodal structure, and the Bogoliubov Fermi surfaces in two directions: we include nonlocal pairing and we consider internal degrees of freedom other than the effective angular momentum of length $j=3/2$ examined so far. Since our main focus is on the Bogoliubov Fermi surfaces, we concentrate on even-parity pairing. The required symmetry analysis is illustrated for several examples, as a guide for the reader. We find that the inclusion of nonlocal pairing leads to a much larger range of possible pairing symmetries. For infinitesimal pairing strength, we find a simple yet powerful criterion for nodes in terms of a scalar product of form factors.

Atomic resolution scanning transmission electron microscopy, based on counting fast electrons that have been scattered to large angles after exciting a phonon, so-called high-angle annular dark-field (HAADF) imaging, is widely used in materials science. Recently atomic resolution phonon spectroscopy has been demonstrated. In both cases experiments are usually modeled taking into account only elastic scattering and the inelastic scattering due to phonon excitation. However, other inelastic processes, such as plasmon excitation and single electron excitation, also play a role. In this paper we will focus on the role of ionization and its influence on imaging and spectroscopy based on phonon excitation. Inelastic scattering due to ionization is mainly forward peaked, which has implications for phonon spectroscopy with a detector in the forward direction. Nevertheless, a substantial fraction of electrons scattered by phonon excitation to larger angles have also lost significant amounts of energy due to also being involved in an ionization event. We discuss the implications of this for HAADF imaging and phonon spectroscopy utilizing electrons scattered to these larger angles.

The search for novel entangled phases of matter has lead to the recent discovery of a new class of “entanglement transitions,” exemplified by random tensor networks and monitored quantum circuits. Most known examples can be understood as some classical ordering transitions in an underlying statistical mechanics model, where entanglement maps onto the free-energy cost of inserting a domain wall. In this paper we study the possibility of entanglement transitions driven by physics beyond such statistical mechanics mappings. Motivated by recent applications of neural-network-inspired variational Ansätze, we investigate under what conditions on the variational parameters these Ansätze can capture an entanglement transition. We study the entanglement scaling of short-range restricted Boltzmann machine (RBM) quantum states with random phases. For uncorrelated random phases, we analytically demonstrate the absence of an entanglement transition and reveal subtle finite-size effects in finite-size numerical simulations. Introducing phases with correlations decaying as $1/r^{\alpha }$ in real space, we observe three regions with a different scaling of entanglement entropy depending on the exponent $\alpha$. We study the nature of the transition between these regions, finding numerical evidence for critical behavior. Our work establishes the presence of long-range correlated phases in RBM-based wave functions as a required ingredient for entanglement transitions.

Two-dimensional ferromagnetic materials have recently been attracted much attention mainly due to their promising applications toward multifunctional devices, e.g., microelectronics, spintronics, and thermoelectric devices. Utilizing the first-principles calculations together with the group theory analysis, we systematically investigate the magnetocrystalline anisotropy energy, magneto-optical effect, and anomalous transport properties (including anomalous Hall, Nernst, and thermal Hall effects) of monolayer and bilayer ${\mathrm{Fe}}_n\mathrm{Ge}{\mathrm{Te}}_2$ ($n=3$, 4, 5). The monolayer ${\mathrm{Fe}}_n\mathrm{Ge}{\mathrm{Te}}_2$ ($n=3$, 4, 5) exhibits the out-of-plane, in-plane, and in-plane ferromagnetic orders with considerable magnetocrystalline anisotropy energies of $-3.17$, 4.42, and 0.58 meV/f.u., respectively. Ferromagnetic order is predicted in bilayer ${\mathrm{Fe}}_4\mathrm{Ge}{\mathrm{Te}}_2$ while antiferromagnetic order is preferred in bilayer ${\mathrm{Fe}}_3\mathrm{Ge}{\mathrm{Te}}_2$ and ${\mathrm{Fe}}_5\mathrm{Ge}{\mathrm{Te}}_2$. The group theory analysis reveals that in addition to monolayer ferromagnetic ${\mathrm{Fe}}_n\mathrm{Ge}{\mathrm{Te}}_2$ ($n=3$, 4, 5), the magneto-optical and anomalous transport phenomena surprisingly exist in bilayer antiferromagnetic ${\mathrm{Fe}}_5\mathrm{Ge}{\mathrm{Te}}_2$, which rare in realistic collinear antiferromagnets. If spin magnetic moments of monolayer and bilayer ${\mathrm{Fe}}_n\mathrm{Ge}{\mathrm{Te}}_2$ are reoriented from the in-plane to out-of-plane direction, then the magneto-optical and anomalous transport properties are enhanced significantly, presenting strong magnetic anisotropy. We also demonstrate that the anomalous Hall effect decreases with the temperature increases. The gigantic anomalous Nernst and thermal Hall effects are found in monolayer and bilayer ferromagnetic ${\mathrm{Fe}}_n\mathrm{Ge}{\mathrm{Te}}_2$, and the largest anomalous Nernst and thermal Hall conductivities, respectively, of $-3.31$ A/Km and 0.22 W/Km at 130 K are observed in bilayer ferromagnetic ${\mathrm{Fe}}_4\mathrm{Ge}{\mathrm{Te}}_2$. In particular, bilayer antiferromagnetic ${\mathrm{Fe}}_5\mathrm{Ge}{\mathrm{Te}}_2$ exhibits large zero-temperature anomalous Hall conductivity of 2.63 $e^2/h$ as well as anomalous Nernst and thermal Hall conductivities of 2.76 A/Km and 0.10 W/Km at 130 K, respectively. Our results suggest that two-dimensional van der Waals magnets ${\mathrm{Fe}}_n\mathrm{Ge}{\mathrm{Te}}_2$ ($n=3$, 4, 5) have great potential applications in magneto-optical devices, spintronics, and spin caloritronics.

We present an empirical description of experimental spin-torque switching probability for the CoFeB/MgO/CoFeB type of magnetic tunnel junctions beyond macrospin limit, parametrizing measurement data for direct comparison with the corresponding macrospin asymptote expression. We show that, near 35 nm in diameter, spin-torque switching speed in these tunnel devices is faster than macrospin-limit predictions. These devices have a faster reduction of switching error rate versus spin-torque drive amplitude than macrospin. While the functional form similar to macrospin can still describe experimental data satisfactorily, the parameters no longer correspond to materials values. Instead they reflect the nonuniform nature of the switching process. Further, the parameters depend on the resistance-area product $r_A$ of the junction, with higher $r_A$ causing a steeper slope of switching error versus switching current. This $r_A$ dependence could not originate from low-bias spin-dependent tunneling. These observations suggest that, in addition to nonuniform nonlinear dynamics during switching, it is also important to consider higher-order dynamic processes, including a high-bias tunnel electron's spin-flip scattering, voltage-induced change to interface magnetism, and possibly Joule heating.

We use large-scale Monte Carlo computations to study the phase transitions between a two-component chiral $p$-wave superconductor and normal state in zero external magnetic field. We find a first-order phase transition from the normal state to a chiral superconducting state, due to interplay between vortices and domain walls.

The Hamiltonian of the magic-angle twisted symmetric trilayer graphene (TSTG) can be decomposed into a twisted-bilayer-graphene- (TBG-) like flat band Hamiltonian and a high-velocity Dirac fermion Hamiltonian. We use Hartree-Fock mean field approach to study the projected Coulomb interacting Hamiltonian of TSTG developed in Călugăru et al. [Phys. Rev. B 103, 195411 (2021)] at integer fillings $\nu =-3,-2,-1$, and 0 measured from charge neutrality. We study the phase diagram with $w_0/w_1$, the ratio of $AA$ and $AB$ interlayer hoppings, and the displacement field, which introduces an interlayer potential $U$ and hybridizes the TBG-like bands with the Dirac bands. At small $U$, we find the ground states at all fillings $\nu$ are in the same phases as the tensor products of a Dirac semimetal with the filling $\nu$ TBG insulator ground states, which are spin-valley polarized at $\nu =-3$, and fully (partially) intervalley coherent at $\nu =-2,0$ ($\nu =-1$) in the flat bands. An exception is $\nu =-3$ with $w_0/w_1\gtrsim 0.7$, which possibly becomes a metal with competing orders at small $U$ due to charge transfers between the Dirac and flat bands. At strong $U$ where the bandwidths exceed interactions, all the fillings $\nu$ enter a metal phase with small or zero valley polarization and intervalley coherence. Lastly, at intermediate $U$, semimetal or insulator phases with zero intervalley coherence may arise for $\nu =-2,-1,0$. Our results provide a simple picture for the electron interactions in TSTG systems, and reveal the connection between the TSTG and TBG ground states.