It is expected that the Gross-Neveu-Yukawa (GNY) chiral Ising transition of Dirac fermions coupled with a scalar field in $(2+1)$ dimensions will be the first fermionic quantum critical point that various methods, such as conformal bootstrap, perturbative renormalization group, and quantum Monte Carlo (QMC) simulations, would yield converged critical exponents—serving the same role as the Ising and $O\left(N\right)$ models in the textbooks of statistical and quantum physics. However, such an expectation has not been fully realized from the lattice QMC simulations due to the obstacles introduced by the UV finite-size effect. In this Letter, by means of the elective-momentum ultrasize (EMUS)-QMC method, we compute the critical exponents of the $O{(N/2)}^2⋊{\mathbb{Z}}_2$ GNY $N=8$ chiral Ising transition on a two-dimensional $\pi$-flux fermion lattice model between Dirac semimetal and quantum spin Hall insulator phases. With the matching of fermionic and bosonic momentum transfer and collective update in momentum space, our QMC results provide fully consistent exponents with those obtained from the bootstrap and perturbative approaches. In this way, the EMUS now live happily on the $N=8$ island and could explore the chiral Gross-Neveu-Yukawa archipelago with ease.

The bulk-edge correspondence is one of the most important ingredients in the theory of topological phases of matter. While the bulk-edge correspondence is applicable for Hermitian junction systems where two subsystems with independent topological invariants are connected to each other, it has not been discussed for junction systems with non-Hermitian point-gap topological phases. In this Letter, based on analytical results obtained by the extension of non-Bloch band theory to junction systems, we establish the bulk-edge correspondence for point-gap topological phases in junction systems. We also confirm that almost all the eigenstates are localized near the interface which are called the “non-Hermitian proximity effects”. One of the unique properties is that the localization length becomes the same for both subsystems, nevertheless those model parameters are different.

Despite numerous applications of two-dimensional (2D) plasmons for electromagnetic energy manipulation at the nanoscale, their quantitative refraction and reflection laws (analogs of Fresnel formulas in optics) have not yet been established. This fact can be traced to the strong nonlocality of equations governing the 2D plasmon propagation. Here, we tackle this difficulty by direct solution of the plasmon scattering problem with the Wiener-Hopf technique. We obtain the reflection and transmission coefficients for 2D plasmons at the discontinuity of 2D conductivity at arbitrary incidence angle, for both gated and nongated 2D systems. At a certain incidence angle, the absolute reflectivity has a pronounced dip, reaching zero for gated plasmons. The dip is associated with wave passage causing no dynamic charge accumulation at the boundary. For all incidence angles, the reflection has a nontrivial phase different from zero and $\pi$.

Dynamical quantum phase transitions occur in dynamically evolving quantum systems when nonanalyticities occur at critical times in the return rate, a dynamical analog of the free energy. This extension of the concept of phase transitions can be brought into contact with another, namely, that of topological phase transitions in which the phase transition is marked by a change in a topological invariant. Following a quantum quench dynamical quantum phase transitions can happen in topological matter, a fact which has already been explored in one-dimensional topological insulators and in two-dimensional Chern insulators. Additionally, in one-dimensional systems a dynamical bulk boundary correspondence has been seen, related to the periodic appearance of zero modes of the Loschmidt echo itself. Here we extend both of these concepts to two-dimensional higher-order topological matter in which the topologically protected boundary modes are corner modes. We consider a minimal model which encompasses all possible forms of higher-order topology in two-dimensional topological band structures. We find that dynamical quantum phase transitions can still occur, and can occur for quenches which cross both bulk and boundary gap closings. Furthermore, a dynamical bulk boundary correspondence is also found, which takes a different form to that in one dimension.

The interaction of ultrashort laser pulses with dielectrics is associated with strong coupling between the material response and the light. The ultrashort pulses excite the materials, and the corresponding rapid changes in optical properties, induced by the generation of free carriers, determine the propagation of the light. In this paper, we describe a self-consistent model for this interaction. The material excitation is described by a model in which the electron dynamics is captured by a set of multiple rate equations coupling energy levels in a conduction band that has been discretized into energy states separated by the photon energy. The propagation of the light is calculated from Maxwell's equations using the finite-difference time-domain approach. The model is used to calculate key observables from laser ablation experiments, e.g., the threshold fluence versus pulse duration and the depth of laser-ablated structures versus fluence, for bulk and thin film samples. For both freestanding thin samples and dielectric stacks, corresponding to high-reflectivity mirrors, the results of the model are strongly influenced by interference phenomena, which significantly influence the material response and ablation. The model is compared to an existing approach using propagation of the intensity envelope of the pulse. In the absence of interference, the two methods predict almost identical ablation thresholds as well as hole depths.

The detection of magnons and their quantum properties, especially in antiferromagnetic (AFM) materials, is a substantial step to realize many ambitious advances in the study of nanomagnetism and the development of energy efficient quantum technologies. The recent development of hybrid systems based on superconducting circuits provides the possibility to engineer quantum sensors that exploit different degrees of freedom. Here, we examine the magnon-photon-transmon hybridization based on bipartite AFM materials, which gives rise to an effective coupling between a transmon qubit and magnons in a bipartite AFM. We demonstrate how magnon modes, their chiralities, and quantum properties, such as nonlocality and two-mode magnon entanglement in bipartite AFMs, can be characterized through the Rabi frequency of the superconducting transmon qubit.

In superconductors, the Higgs amplitude mode is a coherent oscillation of the order parameter typically generated by terahertz laser irradiation. In this paper we propose to probe the Higgs mode using electronic transport in ballistic superconducting hybrid devices. We first confirm the existence of a nonzero amplitude mode in the clean case using the Keldysh-Eilenberger formalism. We then investigate two different device geometries: respectively, a normal-insulator-superconductor (NIS) tunnel junction and a normal-superconducting-normal metal (NSN) junction with two transparent interfaces, the superconductor being irradiated in both situations. In the NIS case, the Higgs manifests itself in the second-order AC current response which is resonant at the Higgs frequency. In the NSN case, the DC differential conductance allows one to probe the gaps dynamically generated by the Higgs mode in the Floquet spectrum.

Recently, nonlocal spatial mirror symmetry breaking metasurfaces have been proposed to generate spatiotemporal optical vortices (STOVs), which carry transverse orbital angular momenta. Here, we investigate the topological property of the STOV generator and show that spatial mirror symmetry breaking introduces a synthetic parameter dimension associated with the metasurface geometry. Furthermore, we demonstrate that there are well-defined vortices emerging with a synthetic parameter dimension, which can topologically protect the STOV generation robustly against structural perturbations and disorders. Since the vortices are always “created” or “annihilated” together in pairs of opposite charges in the $k_x\text{−}\omega$ domain, the total topological charge of these vortices is a conserved quantity. Our studies not only provide a topological perspective for STOV generation but also lay a solid foundation for potential applications of STOV metasurfaces integrated with other optoelectronic devices, because of their robust immunity to fabrication defects.

A new mechanism leading to a switchable Bloch-type polarization in a domain wall separating two ferroelectric domain states is proposed. A biquadratic coupling of the primary order parameter and its gradient originating from inhomogeneous electrostriction triggers the chiral phase transition (Ising-to-Bloch) in the domain walls (DW) with softening of the local polar mode and anomalous increase of the dielectric susceptibility at the phase transition temperature $T_{DW}<T_c$. This mechanism describes the origin and properties of the polar Bloch component, which appears below $T_{DW}$ additionally to the antipolar Néel component in the ${180}^{\circ }$ DW of ${\mathrm{PbTiO}}_3$. The tensile strain of the DW plane promotes the development of the Bloch polarization.

The properties of semiconductors and functional dielectrics are defined by their response in electric fields, which may be perturbed by defects and the strain they generate. In this work, we demonstrate how diffraction-based x-ray microscopy techniques may be utilized to image the electric field in insulating crystalline materials. By analyzing a prototypical ferro- and piezoelectric material, ${\mathrm{BaTiO}}_3$, we identify trends that can guide experimental design towards imaging the electric field using any diffraction-based x-ray microscopy technique. We explain these trends in the context of dark-field x-ray microscopy, but the framework is also valid for Bragg scanning probe x-ray microscopy, Bragg coherent diffraction imaging, and Bragg x-ray ptychography. The ability to quantify electric field distributions alongside the defects and strain already accessible via these techniques offers a more comprehensive picture of the often complex structure-property relationships that exist in many insulating and semiconducting materials.

We show that a two-body Jastrow wave function is able to capture the ground-state properties of the $S=1$ Heisenberg chain with nearest-neighbor superexchange $J$ and single-ion anisotropy term $D$, in both the topological and large-$D$ phases (with $D/J\ge 0$). Here, the optimized Jastrow pseudopotential assumes a very simple form in Fourier space, i.e., $v_q\approx 1/q^2$, which is able to give rise to a finite string-order parameter in the topological regime. The results are analyzed by using an exact mapping from the quantum expectation values over the variational state to the classical partition function of the one-dimensional Coulomb gas of particles with charge $q=\pm 1$. Here, two phases are present at low temperatures: the first one is a diluted gas of dipoles (bound neutral pairs of particles), which are randomly oriented (describing the large-$D$ phase); the other one is a dense liquid of dipoles, which are aligned thanks to the residual dipole-dipole interactions (describing the topological phase, with the finite string order being related to the dipole alignment). Our results provide an insightful interpretation of the ground-state nature of the spin-1 antiferromagnetic Heisenberg model.

We have experimentally studied the Landau levels near the quantum limit in the magnetic Dirac material ($\mathrm{Eu},\mathrm{Gd}){\mathrm{MnBi}}_2$. In this series of materials, the Fermi level is systematically controlled by substituting ${\mathrm{Eu}}^{2+}$ with ${\mathrm{Gd}}^{3+}$ while keeping high mobility. We measured the Shubnikov–de Haas (SdH) oscillation for a single crystal with the lowest hole concentration at tilted magnetic fields up to 20–50 T and clarified the dependence of the splitting of the Landau levels $N\ge 1$ on the ratio of Zeeman energy to cyclotron energy. In the low-field antiferromagnetic phase, the splitting is well explained by the (Zeeman) spin splitting, from which we have found that the effective $g$ factor of the Dirac fermion depends significantly on the Fermi energy. In the high-field antiferromagnetic phase, on the other hand, the SdH oscillation was found to change in a complex manner as a function of the tilt angle of the field, implying the lifting of the valley degeneracy as well as the spin degeneracy.

We present a temperature- and polarization-resolved phononic and electronic Raman scattering study in combination with the first-principles calculations on the kagome metal ${\mathrm{Ni}}_3\mathrm{In}$ with anisotropic transport properties and non-Fermi liquid behavior. At temperatures below 50 K and down to 2 K, several Raman phonon modes, including particularly an interlayer shear mode, exhibit appreciable frequency and linewidth renormalization, reminiscent of the onset of the Kondo screening without an accompanying structural or magnetic phase transition. In addition, a low-energy electronic continuum observed in polarization perpendicular to the kagome planes reveals strong temperature dependence below 50 K, implying thermal depletion of incoherent quasiparticles, while the in-plane continuum remains invariant. These concomitant electronic and phononic Raman signatures suggest that ${\mathrm{Ni}}_3\mathrm{In}$ undergoes an anisotropic electronic crossover from an incoherent to a coherent Kondo lattice regime below 50 K. We discuss the origin of the anisotropic incoherent-coherent crossover in association with the possible anisotropic Kondo hybridization involving localized Ni-$3d_{xz}$ flat-band electrons.

Symmetry-protected topological (SPT) phases exhibit nontrivial short-ranged entanglement protected by symmetry and cannot be adiabatically connected to trivial product states while preserving the symmetry. In contrast, intrinsic topological phases do not need ordinary symmetry to stabilize them and their ground states exhibit long-range entanglement. It is known that for a given symmetry group $G$, the 2D SPT phase protected by $G$ is dual to the 2D topological phase exemplified by the twisted quantum double model $D^{\omega }\left(G\right)$ via gauging the global symmetry $G$. Recently it was realized that such a general gauging map can be implemented by some local unitaries and local measurements when $G$ is a finite, solvable group. Here, we review the general approach to gauging a $G\text{−}\mathrm{SPT}$ starting from a fixed-point ground-state wave function and applying a $N$-step gauging procedure. We provide an in-depth analysis of the intermediate states emerging during the $N$-step gauging and provide tools to measure and identify the emerging symmetry-enriched topological order (SET) of these states. We construct the generic lattice parent Hamiltonians for these intermediate states and show that they form an entangled superposition of a twisted quantum double (TQD) with an SPT-ordered state. Notably, we show that they can be connected to the TQD through a finite-depth, local quantum circuit which does not respect the global symmetry of the SET order. We introduce the so-called symmetry branch line operators and show that they can be used to extract the symmetry fractionalization classes (SFC) and symmetry defectification classes (SDC) of the SET phases with the input data $G$ and $\left[\omega \right]\in H^3(G,U\left(1\right))$ of the pregauged SPT-ordered state. We illustrate the procedure of preparing and characterizing the emerging SET-ordered states for some Abelian and non-Abelian examples such as dihedral groups $D_n$ and the quaternion group $Q_8$.

We study analytically an analog of the Andreev reflection at a normal-superfluid interface. The polariton gapped superfluid region is achieved by quasiresonant optical pumping. The interacting polaritons are described with the driven-dissipative Gross-Pitaevskii equation. We find analytical formulas for the angles and amplitudes of the reflected and transmitted particles. There are limit angles and energies, above which Andreev reflection and transmission cannot be observed anymore and where the Andreev wave becomes a surface mode, exponentially localized on the interface. These properties are confirmed by solving numerically the Gross-Pitaevskii equation in simulations reproducing realistic experimental conditions.

I apply the scattering approach within the framework of macroscopic quantum electrodynamics to derive the variances and mean values of the energy density and intensity for a system of an arbitrary object in an arbitrary environment. To evaluate the temporal bunching character of the energy density and intensity, I determine the ratio of their variances with respect to their mean values. I explicitly evaluate these ratios for the cases of vacuum, a half-space in vacuum, and a sphere in vacuum. Eventually, I extend the applicability of this theory to the case of more than one arbitrary object, independent of the geometrical shapes and materials.

To study the photoinduced processes in strongly correlated electron systems occurring coherently on various time scales, we conducted the pump-probe optical spectroscopy of hexagonal ${\mathrm{YMnO}}_3$ with ranges of delay time between 0.1 and 5000 ps and the energy of light between 1 and 3 eV. We found that the photoinduced changes in reflectivity were dominated by the intra-atomic excitation of a $d$ electron in Mn, by the relaxation of energy from electronic excitations to phonon excitations, by the propagation of a strain wave, and by thermal conduction inside a sample, which occur successively with time. We also found that the sound velocity and thermal conductivity of the sample including their anisotropy can be obtained by this technique.

In this study, we conducted a numerical investigation on the Hall conductance (${\sigma }_{\mathrm{Hall}}$) of graphene based on the magnetic energy band structure calculated using a nonperturbative magnetic-field-containing relativistic tight-binding approximation (MFRTB) method. The nonperturbative MFRTB can revisit two types of plateaus for the dependence of ${\sigma }_{\mathrm{Hall}}$ on Fermi energy. One set is characterized as wide plateaus (WPs). These WPs have filling factors (FFs) of 2, 6, 10, 14, etc., and are known as the half-integer quantum Hall effect. The width of the WPs decreases with increasing FF, which exceeds the decrease expected from the linear dispersion relation of graphene. The other set is characterized by narrow plateaus (NPs), which have FFs of 0, 4, 8, 12, etc. The NPs correspond to the energy gaps caused by the spin-Zeeman effect and spin-orbit interaction. Furthermore, it was discovered that the degeneracy of the magnetic energy bands calculated using the nonperturbative MFRTB method leads to a quantized ${\sigma }_{\mathrm{Hall}}$.

Multiple exciton generation (MEG) is a widely studied phenomenon in semiconductor nanocrystals and quantum dots, aimed at improving the energy conversion efficiency of solar cells. MEG is the process wherein incident photon energy is significantly larger than the band gap, and the resulting photoexcited carriers relax by generating additional electron-hole pairs, rather than decaying by heat dissipation. Here, we present an experimental demonstration of MEG in a prototype strongly correlated material, ${\mathrm{VO}}_2$, through photocurrent spectroscopy and ultrafast transient reflectivity measurements, both of which are considered the most prominent ways for detecting MEG in working devices. The key result of this paper is the observation of MEG at room temperature (in a correlated insulating phase of ${\mathrm{VO}}_2$), and the estimated threshold for MEG is $3E_g$. We demonstrate an escalated photocurrent due to MEG in ${\mathrm{VO}}_2$, and quantum efficiency is found to exceed $100\%$. Our studies suggest that this phenomenon is a manifestation of expeditious impact ionization due to stronger electron correlations and could be exploited in a large number of strongly correlated materials.