We study the impact of plasmon-phonon hybridization on the stopping and image forces acting on a charged particle moving parallel to a graphene-${\mathrm{Al}}_2{\mathrm{O}}_3$-graphene sandwichlike composite system by considering a broad domain in the parameter space. The effective dielectric function of the system is obtained using two descriptions of the electronic response of doped graphene: an ab initio method based on the time-dependent density functional theory calculations and an analytical expression based on the massless Dirac fermion (MDF) approximation for graphene $\pi$ bands. It is found that the main discrepancies between the two methods come from the high-energy interband electron transitions, which are included in the ab initio method but not in the MDF method. Special attention is paid to the regime of low-particle speeds, where the MDF method compares well with the ab initio method, but the modeling is sensitive to the effects of finite temperature and the treatment of phenomenological damping. It is observed at low particle speeds that both forces exhibit an interesting interplay between the hybrid modes of the phononic type and the continuum of the intraband electron-hole excitations in graphene. Furthermore, the effects of the lowest-energy antisymmetric modes, which exhibit acoustic dispersions at long wavelengths in a system with equally doped graphene layers, are exposed in calculations of the stopping force on a co-moving pair of incident particles with opposite charges that are symmetrically positioned around the target system.

We have proposed the generalized temporal coupled-mode theory for a perturbatively parity-time ($\mathcal{PT}$) -symmetric optical resonator, and by utilizing this theory we have expounded successfully a resonance in a perturbatively $\mathcal{PT}$-symmetric photonic heterostructure. The introduction of perturbation changes the variation ranges of the amplitudes of all scattering coefficients. In particular, all amplitudes of scattering coefficients reach infinity simultaneously at the point of critical match. More than that, in the frequency-perturbation space, there is one vortex center for every scattering coefficient at the singular scattering point and one vortex center for each reflection at its minimum. The corresponding quantized topological charges, defined by the winding numbers of scattering coefficients, can also be predicted by our theory successfully. This work is a significant guide to study the resonance in a $\mathcal{PT}$-symmetric optical resonator of the real world.

Oxygen molecules (${\mathrm{O}}_2$) physically adsorbed on solid surfaces are of interest as low-dimensional spin systems. Monolayers of ${\mathrm{O}}_2$ adsorbed on an Ag(111) surface at a low density of less than 1 ML are observed at 4.5 K using scanning tunneling microscopy combined with atomic force microscopy with ${\mathrm{O}}_2$ terminated tips. Various domains with their specific density are mixed, each with different rotation angles to the substrate. The shape of the ${\mathrm{O}}_2$ lattice correlates with the rotation angle between the monolayer and the substrate. The domains with a rotation angle of greater than $1.4^{\circ }$ can be explained by the model of on-line coincidence, which had previously been confirmed only for organic molecules. The coincidence with the substrate naturally explains the observed lattice distortion quantitatively. On the other hand, in domains at the rotation angle near $0^{\circ }$, the lattice distortion is smaller than that of previous study that attributed it to spin. Nevertheless, the length of the shortest distance between two ${\mathrm{O}}_2$ implies antiferromagnetic order.

We report a high-resolution angle-resolved photoemission (ARPES) study of the prototypical nearly free-electron metal sodium. The observed mass enhancement is slightly smaller than that derived in previous studies. The new results on the lifetime broadening increase the demand for theories beyond the random phase approximation. Our results do not support the proposed strong enhancement of the scattering rates of the charge carriers due to a coupling to spin fluctuations. Moreover, a comparison with earlier electron energy-loss data on sodium yields a strong reduction of the mass enhancement of dipolar electron-hole excitations compared to that of monopole hole excitations, measured by ARPES.

Monte Carlo simulations away from half filling suffer from a sign problem that can be reduced by deforming the contour of integration. Such a transformation, which induces a Jacobian determinant in the Boltzmann weight, can be implemented using neural networks. This additional determinant cost for a generic neural network scales cubically with the volume, preventing large-scale simulations. We implement an architecture, based on complex-valued affine coupling layers, which reduces this to linear scaling. We demonstrate the efficacy of this method by successfully applying it to systems of different size, the largest of which is intractable by other Monte Carlo methods due to its severe sign problem.

Using bosonization, we study a model of parallel quantum wires constructed from two-dimensional Dirac fermions in the presence of periodic topological domain walls. The model accounts for the lateral spread of the wave functions $\ell$ in the transverse direction to the wires. The gapless modes confined to each domain wall are shown to form Luttinger liquids, which realize a well-known smectic non-Fermi liquid fixed point when interwire Coulomb interactions are considered. Perturbative studies on phenomenological models have shown that the smectic fixed point is unstable toward a variety of phases such as superconductivity, stripe, smectic, and Fermi liquid phases. Here, we show that the considered model leads to a phase diagram with only smectic metal and Fermi liquid phases. The smectic metal phase is stable in the ideal quantum wire limit $\ell \to 0$. For finite $\ell$, we find a critical Coulomb coupling separating the strong coupling smectic metal from a weak coupling Fermi liquid phase. We conjecture that the absence of superconductivity should be a generic feature of similar models. We discuss the relevance of this model for quantum wires created with moiré heterostructures.

A simple yet paradigmatic model for the interplay of strong electronic correlations and geometric frustration is the triangular lattice Hubbard model. Recently it was proposed that moiré structures of transition metal dichalcogenides can be used to simulate extended versions that include nonlocal density-density interactions. We study competing instabilities of interacting electrons in such an extended Hubbard model on the triangular lattice near a filling where the density of states has a Van Hove singularity. We employ a truncated-unity functional renormalization group approach to investigate two cases: a paradigmatic minimally extended Hubbard model and a specific model with parameters that are applicable to heterobilayers of transition metal dichalcogenides. We unravel rich phase diagrams, including tendencies to spin-density-wave order and unconventional pairing, which can give rise to topological superconductivity. We classify the symmetry of the superconducting instabilities according to their irreducible representations and show that higher lattice harmonics are dominant when the nearest-neighbor interaction is sizable indicating pair formation between second-nearest neighbors. The phenomenological consequences can be enhanced spin and thermal quantum Hall responses in a topological superconductor.

We analytically determine the energy gap at weak coupling in the attractive multicomponent Gaudin-Yang model, an integrable model which describes interacting fermions in one dimension with $\kappa$ components. We use three different methods. The first one is based on a direct analysis of the Bethe ansatz equations. The second method uses the theory of resurgence and the large order behavior of the perturbative series for the ground state energy. The third method is based on a renormalization group analysis. The three methods lead to the same answer, providing in this way a nontrivial test of the ideas of resurgence and renormalons as applied to nonrelativistic many-body systems.

A generic semiclassical superconducting nanostructure connected to multiple superconducting terminals hosts a quasicontinuous spectrum of Andreev states. The spectrum is sensitive to the superconducting phases of the terminals. It can be either gapped or gapless depending on the point in the multidimensional parametric space of these phases. Special points in this space correspond to setting some terminals to the phase 0 and the rest to the phase of $\pi$. For a generic nanostructure, three distinct spectra come together in the vicinity of a special point: two gapped phases of different topology and a gapless phase separating the two by virtue of topological protection. In this paper, we show that a weak interaction manifesting as quantum fluctuations of superconducting phases drastically changes the spectrum in a narrow vicinity of a special point. We develop an interaction model and derive a universal generic quantum action that describes this situation. The action is complicated incorporating a nonlocal in time matrix order parameter, and its full analysis is beyond the scope of the present paper. Here, we identify and address two limits: the semiclassical one and the quantum one, concentrating on the first-order interaction correction in the last case. In both cases, we find that the interaction squeezes the domain of the gapless phase in the narrow vicinity of the point so the gapped phases tend to contact each other immediately defying the topological protection. We identify the domains of strong coupling where the perturbation theory does not work. In the gapless phase, we find the logarithmic divergence of the first-order corrections. This leads us to an interesting hypothesis: weak interaction might induce an exponentially small gap in the formerly gapless phase.

We use atomistic simulations to study the interactions between two-dimensional domain walls and Sr inclusions in the prototypical ferroelectric ${\mathrm{BaTiO}}_3$. Based on nudged elastic band calculations we predict that the energy barrier for domain-wall movement increases in the vicinity of small planar Sr inclusions which may act as pinning centers. We link this observation to the local increase in polarization by larger oxygen off-centering and validate our predictions by molecular dynamics simulations of field-driven domain walls at finite temperatures.

Superconducting devices subject to strong charging energy interactions and Coulomb blockade are one of the key elements for the development of nanoelectronics and constitute common building blocks of quantum computation platforms and topological superconducting setups. The study of their transport properties is nontrivial and some of their nonperturbative aspects are hard to capture with the most ordinary techniques. Here we present a matrix product state approach to simulate the real-time dynamics of these systems. We propose a study of their transport based on the analysis of the currents after quantum quenches connecting such devices with external leads. Our method is based on the combination of a Wilson chain construction for the leads and a mean-field BCS description for the superconducting scatterers. In particular, we employ a quasiparticle energy eigenbasis which greatly reduces their entanglement growth and we introduce an auxiliary degree of freedom to encode the device's total charge. This approach allows us to treat nonperturbatively both their charging energy and coupling with external electrodes. We show that our construction is able to describe the Coulomb diamond structure of a superconducting dot with subgap states, including its sequential tunneling and cotunneling features. We also study the conductance zero-bias peaks caused by Majorana modes in a blockaded Kitaev chain and compare our results with common Breit-Wigner predictions.

Nonequilibrium quantum dynamics can give rise to the emergence of novel steady states. We propose a scheme for driving an initially uncorrelated thermal state to generate customized correlation functions by determining and reverse engineering the steady-state two-point functions for a class of Markov processes. We also extend the formalism to the calculation of four-point functions. We then apply our method to generating power-law correlated fermionic Green's functions. Furthermore, we find that the power-law patterns emerge at much shorter times than the convergence to the steady state, at which point the disorder in the two-point correlations disappears. On the other hand, the density-density correlations exhibit steady-state disorder while following a power-law trend line. These ideal steady states appear as intermediate-time quasi-steady states in the presence of perturbations.

Renormalization-group theory predicts that the XXZ antiferromagnet in a magnetic field along the easy $Z$ axis has asymptotically either a tetracritical phase diagram or a triple point in the field-temperature plane. Neither experiments nor Monte Carlo simulations procure such phase diagrams. Instead, they find a bicritical phase diagram. Here, this discrepancy is resolved: After generalizing a ubiquitous condition identifying the tetracritical point, we employ different renormalization-group recursion relations near the isotropic fixed point, exploiting group-theoretical considerations and using accurate exponents at three dimensions. These show that the results from experiments and simulations can only be understood if their trajectories flow towards the fluctuation-driven first-order transition (and the associated triple point), but reach this limit only for prohibitively large system sizes or correlation lengths. In the crossover region one expects a bicritical phase diagram, as indeed is observed. A similar scenario may explain puzzling discrepancies between simulations and renormalization-group predictions for a variety of other phase diagrams with competing order parameters.

Giant thermoelectric effects are known to arise at the interface between superconductors and strongly polarized ferromagnets, enabling the construction of efficient thermoelectric generators. We predict that the thermopower of such a generator can be completely controlled by a magnetic input signal: Not only can the thermopower be toggled on and off by rotating a magnet, but it can even be entirely reversed. This in situ control diverges from conventional thermoelectrics, where the thermopower is usually fixed by the device design.

It is well known that Anderson transition is a disorder-induced metal-insulator transition. Contrary to this conventional wisdom, some investigations have shown that disorders could destroy the phase coherence of localized modes in flat bands, making the localized states melt into extended states. This phenomenon is called the inverse Anderson transition. To date, the experimental observation of inverse Anderson transitions is still lacking. In this work, we report the implementation of inverse Anderson transitions based on Aharonov-Bohm topolectrical circuits. Different types of disorders, including symmetric-correlated, antisymmetric-correlated, and uncorrelated disorders, can be easily implemented in Aharonov-Bohm circuits by engineering the spatial distribution of ground settings. Through the direct measurements of frequency-dependent impedance responses and time-domain voltage dynamics, the inverse Anderson transitions induced by antisymmetric-correlated disorders are clearly observed. Moreover, the flat bands and associated spatial localizations are also fulfilled in clean Aharonov-Bohm circuits or Aharonov-Bohm circuits sustaining symmetric-correlated and uncorrelated disorders, respectively. Our proposal provides a flexible platform to investigate the interplay between the geometric localization and Anderson localization, and could have potential applications in electronic signal control.

Quantum information spreading and scrambling in many-body systems attract interest these days. Tripartite mutual information (TMI) based on operator-based entanglement entropy (EE) is an efficient tool for measuring them. In this paper, we study random spin chains that exhibit phase transitions accompanying nontrivial changes in topological properties. In their phase diagrams, there are two types of many-body localized (MBL) states and one thermalized regime intervening these two MBL states. Quench dynamics of the EE and TMI display interesting behaviors, providing an essential perspective concerning the encoding of quantum information. In particular, one of the models is self-dual, but information spreading measured by the TMI does not respect this self-duality. We investigate this phenomenon from the viewpoint of spatial structure of the stabilizers. In general, we find that knowledge of the phase diagram corresponding to the qubit system is useful for understanding the nature of quantum information spreading in that system. The connection between the present paper and random circuit of projective measurements and also topological Majorana quantum memory is remarked upon.

A quasiperiodic system is an intermediate state between periodic and disordered systems with a unique delocalization-localization transition driven by the quasiperiodic potential (QP). One of the intriguing questions is whether the universality class of the Anderson transition (AT) driven by QP is similar to that of the AT driven by the random potential in the same symmetry class. Here, we study the critical behavior of the ATs driven by QP in the three-dimensional (3D) Anderson model, the Peierls phase model, and the Ando model, which belong to the Wigner-Dyson symmetry classes. The localization length and two-terminal conductance have been calculated using the transfer-matrix method, and we argue that their error estimations in statistics suffer from the correlation of QP. With the correlation under control, the critical exponents $\nu$ of the ATs driven by QP are estimated by the finite-size scaling analysis of conductance, and they are consistent with the exponents $\nu$ of the ATs driven by the random potential. Moreover, the critical conductance distribution and the level spacing ratio distribution have been studied. We also find that a convolutional neural network trained by the localized/delocalized wave functions in a disordered system predicts the localization/delocalization of the wave functions in quasiperiodic systems. Our numerical results strongly support the idea that the universality classes of the ATs driven by QP and the random potential are similar in the 3D Wigner-Dyson symmetry classes.

The ${\mathrm{Cr}}^{4+}$ oxidation state with two electrons in the $\mathrm{Cr}3d$ shell is not often observed in perovskite-type oxides, as high pressures and temperatures are generally required to stabilize the octahedral coordination. Herein, we present a comparative study of the half-doped perovskite-type chromites ${\mathrm{Gd}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{CrO}}_3$ (GSCO) and ${\mathrm{Gd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{CrO}}_3$ (GCCO). Fifty percent of the Cr occurs in the ${\mathrm{Cr}}^{4+}$ oxidation state after high-pressure synthesis at 6 GPa and 1200 °C. The materials were investigated using synchrotron x-ray diffraction, magnetization, heat capacity, and dielectric measurements. The diffraction patterns show that GSCO and GCCO crystallize in orthorhombic ($Pnma$) structures with different degrees of local lattice distortion. GSCO exhibits a long-range magnetic order at temperatures of $<98\mathrm{K}$, accompanied by magnetization reversal, suggesting that the magnetic ground state is ferrimagnetic. In contrast, GCCO displays antiferromagnetic characters at temperatures $<\sim 100\mathrm{K}$. In addition, GSCO exhibits a crossover between conventional and inverse exchange bias effects at low temperatures ($<50\mathrm{K}$). This is likely caused by asymmetric exchange Dzyaloshinskii-Moriya interactions between the Cr ions of different valences (+3 and +4). Furthermore, significant magnetoelectric coupling at the onset of the magnetic order is supported by temperature-dependent dielectric measurements.

Orthoferrites ($R{\mathrm{FeO}}_3$) containing rare-earth ($R$) elements are 3D antiferromagnets (AFMs) that exhibit characteristic weak ferromagnetism originating due to slight canting of the spin moments and display a rich variety of spin-reorientation transitions in the magnetic field ($H$)-temperature ($T$) parameter space. We present spin Hall magnetoresistance (SMR) studies on a $b$ plate ($\mathit{ac}$ plane) of crystalline ${\mathrm{Ho}}_{0.5}{\mathrm{Dy}}_{0.5}{\mathrm{FeO}}_3|\mathrm{Pt}$ hybrid at various $T$ in the range 11–300 K. In the room temperature ${\mathrm{\Gamma }}_4$ phase, the switching between two degenerate domains occurs at fields above a critical value, $H_{\text{c}}\approx 713$ Oe. Under $H>H_{\text{c}}$, the angular dependence of SMR ($\alpha$ scan) yielded a highly skewed curve with a sharp change (sign-reversal) along with a rotational hysteresis around the $\mathit{a}$ axis. Notably, at $H<H_{\text{c}}$, the $\alpha$-scan measurements on the single degenerate domain exhibited an anomalous sinusoidal signal of periodicity ${360}^{\circ }$. Low-$T$ evolution of the SMR curves ($H$ = 2.4 kOe) suggests weakening of the anisotropy possibly due to the $T$ evolution of Fe-$R$ exchange coupling. Below 25 K, the SMR modulation showed an abrupt change around the $\mathit{c}$ axis, marking the presence of a ${\mathrm{\Gamma }}_2$ phase. We have employed a simple Hamiltonian and computed SMR to examine the observed skewed SMR modulation. In summary, SMR is found to be an effective tool to probe magnetic anisotropy as well as a spin reorientation in ${\mathrm{Ho}}_{0.5}{\mathrm{Dy}}_{0.5}{\mathrm{FeO}}_3$. Our spin-transport study highlights the potential of ${\mathrm{Ho}}_{0.5}{\mathrm{Dy}}_{0.5}{\mathrm{FeO}}_3$ for future AFM spintronic devices.

We study quantum multicritical behavior in a $(2+1)\text{−}\mathrm{dimensional}$ Gross-Neveu-Yukawa field theory with eight-component Dirac fermions coupled to two triplets of order parameters that act as Dirac masses and transform as $(1,0)+(0,1)$ representation under the $\mathrm{S}\mathrm{O}\left(4\right)\simeq \mathrm{S}\mathrm{O}\left(3\right)\times \mathrm{SO}\left(3\right)$ symmetry group. This field theory is relevant to spin-1/2 fermions on honeycomb or $\pi$-flux lattices, for example, near the transition points between an $s$-wave superconductor and a charge-density wave, on one side, and Néel order, on the other. Two triplets of such order parameters always allow for a common pair of two other order parameters that would complete them to the maximal set of compatible (anticommuting) orders of five. We first derive a unitary transformation in the Nambu (particle-hole) space which maps any two such triplets, possibly containing some superconducting orders, onto purely insulating order parameters. This allows one to consider a universal SO(4) Gross-Neveu-Yukawa description of the multicriticality without any Nambu doubling. We then proceed to derive the renormalization-group flow of the coupling constants at one-loop order in $4-\epsilon$ space-time dimensions, allowing also a more general set of order parameters transforming under $\mathrm{S}\mathrm{O}\left(n_a\right)\times \mathrm{S}\mathrm{O}\left(n_b\right)$. While for $n_a=n_b>2$ in the bosonic sector and with fermions decoupled there is a stable fixed point of the flow, the Yukawa coupling to fermions quickly leads to its elimination by a generic fixed-point collision in the relevant range of fermion flavor numbers $N_f$. This suggests the replacement of the critical behavior by a runaway flow in the physical case $n_a=n_b=3$. The structure of the renormalization group flow at $n_a\ne n_b$ is also discussed, and some nonperturbative arguments in favor of the stability of the decoupled critical point when $n_a=3$ and $n_b=1$ in $D=2+1$ are provided.