Bulk chalcogenide perovskite $\mathrm{BaZr}{\mathrm{S}}_3$ (BZS), with a direct band gap in the visible region, is an important photovoltaic material, albeit with limited applicability owing to its antiferroelectric (AF) nature. Presently, ferroelectric (FE) perovskite-based photovoltaics are attracting enormous attention for environmental stability and better energy conversion efficiency through enhanced charge separation. We report on AF-FE phases of BZS thin film using temperature-dependent Raman investigations and first-principles calculations. Origin of localized FE phase is established from an anomalous behavior of $A_g^7\sim 300\mathrm{c}{\mathrm{m}}^{-1}$ and $B_{1g}^5\sim 420\mathrm{c}{\mathrm{m}}^{-1}$ modes, which involve the vibration of atoms at the apical site of $\mathrm{Zr}{\mathrm{S}}_6$ octahedra. Additionally, $B_{1g}^1$ and $B_{2g}^2$ ($\sim 85\mathrm{c}{\mathrm{m}}^{-1}$) modes appear while antipolar $B_{2g}^1$ ($\sim 60\mathrm{c}{\mathrm{m}}^{-1}$) disappears below 60 K. Our first-principles calculations confirm that FE appears as a result of the loss of center of inversion symmetry in $\mathrm{Zr}{\mathrm{S}}_6$ due to the existence of oxygen impurities placed locally at apical sites of sulfur.

We report spatially resolved measurements of free carrier collective excitations in a doped semiconductor. Using $\sim 10$ meV resolution electron energy loss spectroscopy (EELS) in an electron microscope with $\AA$ spatial resolution, we identify both surface and bulk carrier plasmons at infrared energies in a freestanding film of indium tin oxide (ITO). The interference patterns of long wavelength propagating surface carrier plasmons are revealed using spatially resolved EELS, from which we extract a dispersion relation. We further show that the energies of these plasmons vary near the surfaces and grain boundaries of the film due to band bending. Modeling based on dielectric theory agrees very well with experimental results. Finally, carrier plasmons in amorphous and crystalline ITO films are compared. These results should also be helpful for understanding the free carrier plasmons in other doped semiconductors in nanoscale volumes.

Light scattering by nanoparticles can be well understood and manipulated in the framework of induced electromagnetic multipoles. Conventionally, the scattering properties of light by nanoparticles are considered to be a result of superposition of the radiation from the induced multipoles due to their orthogonality. Here, we reveal that the interaction between the electric and magnetic dipoles in adjacent nanoparticles can provide an additional route to manipulate light scattering. Specifically, we show that an all-dielectric dimer can support the magnetoelectric coupling effect, in which the electric/magnetic dipole in one nanoparticle can induce an additional magnetic/electric dipole in the other nanoparticle. Such additional electric and magnetic dipoles can suppress or enhance light extinction, which is determined by the phase relationship with respect to the incident field. Furthermore, the magnetoelectric coupling induced dipoles can modify the far-field scattering pattern and even realize unidirectional forward scattering. As a proof-of-principle demonstration, experimental measurements at microwave frequency were performed, and the results are in good agreement with the theoretical ones. Our results may pave the way for manipulating light scattering and novel wave phenomena with magnetoelectric coupling.

The dynamic polarization for Kekulé-patterned graphene is studied within the random phase approximation (RPA). It is shown how the breaking of the valley degeneracy by the lattice modulation is manifested through the dielectric spectrum, the plasmonic dispersion, the static screening, and the optical conductivity. The valley-dependent splitting of the Fermi velocities due to the Kekulé distortion leads to a similar splitting in the dielectric spectrum of graphene, introducing new characteristic frequencies, which are given in terms of the valley-coupling amplitude. The valley coupling also splits the plasmonic dispersion, introducing a second branch in the Landau damping region. Finally, the signatures of the broken valley degeneracy in the optical conductivity are studied. The characteristic steplike spectrum of graphene is split into two half steps due to the onset of absorption in each valley occurring at different characteristic frequencies. Also, an absorption phenomenon was found where a resonance peak related to intervalley transport emerges at a “beat frequency,” determined by the difference between the characteristic frequencies of each valley. Some of these mechanisms are expected to be present in other space-modulated 2D materials and suggest how optical or electrical response measurements can be suitable to detect spatial modulation.

Robust engineering of phonon squeezed states in optically excited solids has emerged as a promising tool to control and manipulate their properties. However, in contrast to quantum optical systems, detection of phonon squeezing is subtle and elusive, and an important question is what constitutes an unambiguous signature of it. The state of the art involves observing oscillations at twice the phonon frequency in time-resolved measurements of the out-of-equilibrium phonon fluctuation. Using the Keldysh formalism we show that such a signal is a necessary but not a sufficient signature of a squeezed phonon, since we identify several mechanisms that do not involve squeezing and yet produce similar oscillations. We show that reliable detection requires a time- and frequency-resolved measurement of the phonon spectral function.

Contrary to the starting assumption of Grbić et al. [Phys. Rev. B 83, 144508 (2011)], here we will argue that a 16-T magnetic field is not enough to quench all superconducting fluctuations above $T_c$ in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. We conclude that through their measurements of microwave absorption these authors actually determine the AC fluctuation magnetoconductivity at 16 T, instead of the zero-field AC paraconductivity as they contend. So the temperature proposed by Grbić et al. for the onset of the superconducting fluctuations, $T^{\prime }$, will correspond to the one at which the finite-field effects at 16 T become measurable in their experiments and the actual fluctuation onset will be located well above $T^{\prime }$. These conclusions, which also concern influential recent publications on that issue, are confirmed by analyzing some of the Grbić et al. data on the grounds of the Gaussian Ginzburg-Landau approach for the finite-field (or Prange) fluctuation regime.

In a previous article [M. S. Grbić et al., Phys. Rev. B 83, 144508 (2011)] we reported data on the high-temperature superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ collected by a contactless microwave absorption technique, which provided evidence for superconducting correlations over a limited temperature range (10–20 K above $T_c$). The paraconductivity signal was determined by subtraction of zero-magnetic-field data from 16-T data. In the preceding Comment [D. Sóñora et al., preceding Comment, Phys. Rev. B 102, 176501 (2020)] D. Sóñora et al. argue that a 16-T magnetic field is not enough to quench all superconducting fluctuations in the microwave spectral range above $T_c$. As is obvious from the experimental data presented here, as well as from the data shown in the original paper, such conclusions disagree with our experimental results. Moreover, our initial experimental findings recently received independent robust confirmation from several different experimental techniques.

We show how complex modulated order can spontaneously emerge when magnetic interactions compete in a metal with polar lattice distortions. Combining neutron and resonant x-ray scattering with symmetry analysis, we reveal that the spin reorientation in ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ is mediated by a magnetic cycloid whose eccentricity evolves smoothly but rapidly with temperature. We find the cycloid to be highly sensitive to magnetic fields, which appear to continuously generate higher harmonic modulations. Our results provide a unified picture of the rich magnetic phases of this correlated, multiband polar metal.

Using voltage fluctuation spectroscopy, we observe the mode locking phenomena of current-induced skyrmion-lattice motion in microfabricated MnSi. When only a dc electric current is applied, the frequency of the emergent narrow-band noise (NBN) monotonously increases with increasing dc current. By contrast, if an ac electric current is further added, the NBN frequency becomes much less dependent on the dc current when it satisfies a simple integer ratio to the ac current frequency, a hallmark of mode locking. In the mode locked state, the linewidth of the NBN is sharpened, indicating the enhanced coherence of the skyrmion-lattice motion. The overall features of the mode locking phenomena are qualitatively reproduced within the framework of the classical rigid-sphere model.

We formulate a new “Wigner characteristics”-based method to calculate entanglement entropies of subsystems of Fermions using Keldysh field theory. This bypasses the requirements of working with complicated manifolds for calculating Rényi entropies for many-body systems. We provide an exact analytic formula for Rényi and von Neumann entanglement entropies of noninteracting open quantum systems, which are initialized in arbitrary Fock states. We use this formalism to look at entanglement entropies of momentum Fock states of one-dimensional Fermions. We show that the entanglement entropy of a Fock state can scale either logarithmically or linearly with subsystem size, depending on whether the number of discontinuities in the momentum distribution is smaller or larger than the subsystem size. We also use this formalism to describe entanglement dynamics of an open quantum system starting with a single domain wall at the center of the system. Using entanglement entropy and mutual information, we understand the dynamics in terms of coherent motion of the domain wall wavefronts, creation and annihilation of domain walls, and incoherent exchange of particles with the bath.

Superconducting materials with noncentrosymmetric lattices lacking space inversion symmetry exhibit a variety of interesting parity-breaking phenomena, including the magnetoelectric effect, spin-polarized currents, helical states, and the unusual Josephson effect. We demonstrate, within a Ginzburg-Landau framework describing noncentrosymmetric superconductors with $O$ point group symmetry, that vortices can exhibit an inversion of the magnetic field at a certain distance from the vortex core. In stark contrast to conventional superconducting vortices, the magnetic-field reversal in the parity-broken superconductor leads to nonmonotonic intervortex forces, and, as a consequence, to the exotic properties of the vortex matter such as the formation of vortex bound states, vortex clusters, and the appearance of metastable vortex/antivortex bound states.

We discuss the unconventional magnetic response and vortex states arising in noncentrosymmetric superconductors with chiral octahedral and tetrahedral ($O$ or $T$) symmetry. We microscopically derive Ginzburg-Landau free energy. It is shown that due to spin-orbit and Zeeman coupling magnetic response of the system can change very significantly with temperature. For sufficiently strong coupling this leads to a crossover from type-1 superconductivity at elevated temperature to vortex states at lower temperature. The external magnetic field decay in such superconductors does not have the simple exponential law. We show that in the London limit, magnetic field can be solved in terms of complex force-free fields $\vec{W}$, which are defined by $\mathbf{\nabla }\times \vec{W}=\text{const}\vec{W}$. Using that we demonstrate that the magnetic field of a vortex decays in spirals. Because of such behavior of the magnetic field, the intervortex and vortex-boundary interaction becomes nonmonotonic with multiple minima. This implies that vortices form bound states with other vortices, antivortices, and boundaries.

The intrinsic spin Hall effect plays an important role in spintronics applications, such as spin-orbit torque-based memory. The bulk space group symmetry determines the form of the bulk spin current conductivity tensor. This paper considers materials for which the local point group symmetry of individual atoms is lower than the global (bulk) symmetry. This enables a position-dependent spin current response, with additional tensor components allowed relative to the bulk response. We present a general method to compute the position-dependent intrinsic spin Hall conductivity, with similar computational effort relative to computing the bulk spin Hall conductivity. We also present the general symmetry-constrained form of the position-dependent spin current response. We apply this method to $1T^{\prime }\text{−}{\mathrm{WTe}}_2$, which exhibits a conventional spin Hall conductivity tensor component ${\sigma }_{xz}^y$ and a staggered unconventional component ${\sigma }_{xz}^z$. The magnitude of these two components, around 100 and 20 ${\left(\mathrm{\Omega }\text{cm}\right)}^{-1}$, respectively, are comparable to the spin-orbit torque exerted on adjacent ferromagnets in experiments. We then consider orthorhombic PbTe, in which both uniform and staggered spin current conductivity are one order of magnitude larger.

Based on density functional theory and density functional perturbation theory calculations, we systematically investigate the vibration responses of monolayer $1H\text{−}{\mathrm{MoTe}}_2$ to equibiaxial strains. It is found that, at the $\mathrm{\Gamma }$ point, the frequency shift of Raman-active modes $(E^{\prime },$ $A_1^{\prime },$ and $E^{″})$ and infrared-active modes $(A_2^{″}$ and $E^{\prime })$ show domelike shapes; that is, their frequencies decrease monotonically under tensile strains but first increase and then decrease rapidly under compressive strains. The frequency-shift behaviors are revealed to come from vibration responses to both bond stretching and bond-angle bending in strained $1H\text{−}{\mathrm{MoTe}}_2$. At the $K$ point, a special acoustic mode becomes soft because its frequency drops to zero at a compressive strain of $-11.27\%$. We find that electron occupancies in Mo $d_{z^2}$, Te $p_x$, and Te $p_y$ orbitals weaken the vibration mode at $K$, which exhibits the in-plane vibration of Mo atoms and out-of-plane vibration of Te atoms. On the other hand, compressive strains enhance the Fermi surface nesting and abruptly soften the vibration frequency for one acoustic mode at $K$. Our results point out a way to detect the strain status of monolayer $1H\text{−}{\mathrm{MoTe}}_2$ by measuring the vibration frequencies.

Polar dielectric nanoresonators can support hybrid photon-phonon modes termed surface phonon polaritons with length scales below the diffraction limit. In the deep subwavelength regime the optical response of these systems was shown to diverge from that predicted through a standard dielectric description. Recently, we developed an analytical, dielectric approach and applied it to spheres and planar heterostructures, reproducing anomalous features observed in experiment and microscopic calculations. In this Rapid Communication we develop tools to describe the nonlocal response of polar nanoresonators of arbitrary symmetry, and use them to investigate systems with nanogaps and nanolayers of practical technological relevance. We demonstrate that the available field enhancement is strongly reduced, as the electromagnetic energy leaks away from the hot spots, while phononic resonances are shifted by resonator effects.

We present a generic, compact formula for the current flowing in interacting and noninteracting systems which are driven out of equilibrium by biased reservoirs described by Lindblad jump operators. We show that, in the limit of high temperature and chemical potential, our formula is equivalent to the well-known Meir-Wingreen formula, which describes the current flowing through a system connected to fermionic baths, therefore bridging the gap between the two formalisms. Our formulation gives a systematic way to address the transport properties of correlated systems strongly driven out of equilibrium. As an illustration, we provide explicit calculations of the current in three cases : (i) a single-site impurity, (ii) a free-fermionic chain, and (iii) a fermionic chain with loss and gain terms along the chain. In this last case, we find that the current across the system has the same behavior for loss or gain terms and depends on the loss/gain rate in a nonmonotonic way.

We use time-resolved x-ray resonant magnetic scattering (TR-XRMS) at the Co $M_{2,3}$ and Tb $O_1$ edges to study ultrafast demagnetization in an amorphous ${\mathrm{Co}}_{88}{\mathrm{Tb}}_{12}$ alloy with stripe domains. Combining the femtosecond temporal with nanometer spatial resolution of our experiment, we demonstrate that the equilibrium spin texture of the thin film remains unaltered by the optical pump pulse on ultrashort timescales ($<1\mathrm{ps}$). However, after $\simeq 4$ ps, we observe the onset of a significant domain wall broadening, which we attribute to a reduction of the uniaxial magnetic anisotropy of the system, due to energy transfer to the lattice. Static temperature-dependent magnetometry measurements combined with analytical modeling of the magnetic structure of the thin film corroborate this interpretation.

First-principles calculations and a model consideration of magnetically frustrated layered material ${\mathrm{PdCrO}}_2$ are performed. The results on the exchange parameters are in agreement with the experimental data on the Curie-Weiss temperature ($\theta$). We show that experimentally observed strong suppression of the Néel temperature ($T_N$) in comparison with the Curie-Weiss temperature is due to three main factors. First, as expected, this is connected with the layered structure and relatively small exchange interaction along the $c$ axis. Second, deformation of the ideal in-plane ${120}^{\circ }$ magnetic structure is crucial to provide finite $T_N$ value. However, these two factors are still insufficient to explain low $T_N$ and the large frustration factor $\left|\theta \right|/T_N$. Thus, we suggest a scenario of an exotic non-Fermi-liquid state in ${\mathrm{PdCrO}}_2$ above $T_N$ within the frameworks of the Anderson lattice model, which seems to explain qualitatively all its main peculiarities.