The short-range order (SRO) and medium-range order of electrostatically levitated $\mathrm{Z}{\mathrm{r}}_{80}\mathrm{P}{\mathrm{t}}_{20}$ and $\mathrm{Z}{\mathrm{r}}_{77}\mathrm{R}{\mathrm{h}}_{23}$ liquids are presented based on a combination of high-energy x-ray diffraction and time-of-flight neutron diffraction studies. The atomic structures of the $\mathrm{Z}{\mathrm{r}}_{80}\mathrm{P}{\mathrm{t}}_{20}$ liquids were determined as a function of temperature from constrained reverse Monte Carlo simulations using x-ray and elastic neutron scattering measurements and two partial pair-distribution functions obtained from molecular dynamics (MD) simulations. Analysis of both the Faber-Ziman and Bhatia-Thornton partial structure factors shows that the $\mathrm{Z}{\mathrm{r}}_{80}\mathrm{P}{\mathrm{t}}_{20}$ and $\mathrm{Z}{\mathrm{r}}_{77}\mathrm{R}{\mathrm{h}}_{23}$ liquids have similar topological SRO. Interestingly, the chemical SRO appears to be much more strongly tied to the topological order in the $\mathrm{Z}{\mathrm{r}}_{77}\mathrm{R}{\mathrm{h}}_{23}$ liquid than in the $\mathrm{Z}{\mathrm{r}}_{80}\mathrm{P}{\mathrm{t}}_{20}$. These results demonstrate that the combination of experimental scattering measurements with MD results provides a powerful approach for obtaining details of chemical and topological ordering in metallic glasses and liquids.

Magnetic structures with controlled domain wall pattern may be applied as potential building blocks for three-dimensional magnetic memory and logic devices. Using a unique electrochemical self-assembly method, we achieve regular single-crystalline cobalt filament arrays with specific geometric profile and crystallographic orientation, and the magnetic domain configuration can be conveniently tailored. We report the transition of periodic antiparallel magnetic domains to compressed vortex magnetic domains depending on the ratio of height to width of the wires. A “phase diagram” is obtained to describe the dependence of the type of magnetic domain and the geometrical profiles of the wires. Magnetoresistance of the filaments demonstrates that the contribution of a series of ${180}^{\circ }$ domain walls is over $0.15\%$ of the zero-field resistance $\rho (H=0)$. These self-assembled magnetic nanofilaments, with controlled periodic domain patterns, offer an interesting platform to explore domain-wall-based memory and logic devices.

We consider the easy-plane limit of bipartite $\mathrm{SU}(N$) Heisenberg Hamiltonians, which have a fundamental representation on one sublattice and the conjugate to fundamental on the other sublattice. For $N=2$ the easy plane limit of the SU(2) Heisenberg model is the well-known quantum $XY$ model of a lattice superfluid. We introduce a logical method to generalize the quantum $XY$ model to arbitrary $N$, which keeps the Hamiltonian sign-free. We show that these quantum Hamiltonians have a world-line representation as the statistical mechanics of certain tightly packed loop models of $N$ colors in which neighboring loops are disallowed from having the same color. In this loop representation we design an efficient Monte Carlo cluster algorithm for our model. We present extensive numerical results for these models on the two dimensional square lattice, where we find the nearest neighbor model has superfluid order for $N\le 5$ and valence-bond order for $N>5$. By introducing $\mathrm{SU}(N$) easy-plane symmetric four-spin couplings we are able to tune across the superfluid-VBS phase boundary for all $N\le 5$. We present clear evidence that this quantum phase transition is first order for $N=2$ and $N=5$, suggesting that easy-plane deconfined criticality runs away generically to a first-order transition for small $N$.

We show that the dynamical freezing of vortex structures nucleated at diluted densities in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_8$ samples with a dense distribution of columnar defects, $B\sim {10}^{-2}{B}_{\mathrm{\Phi }}$ with $B_{\mathrm{\Phi }}=5\mathrm{kG}$, results in configurations with liquidlike correlations. We propose a freezing model considering a relaxation dynamics dominated by double-kink excitations driven by the local stresses obtained directly from experimental images. With this model we estimate the relaxation barrier and the freezing temperature. We argue that the low-field frozen vortex structures nucleated in a dense distribution of columnar defects thus correspond to an out-of-equilibrium nonentangled liquid with strongly reduced mobility rather than to a snapshot of a metastable state with divergent activation barriers as, for instance, expected for the Bose-glass phase at equilibrium.

Pair distribution functions of ferroelectric $x{\mathrm{BiScO}}_3\text{−}\left(1-x\right){\mathrm{PbTiO}}_3$, obtained from neutron total scattering data, were examined and modeled utilizing the reverse Monte Carlo technique to depict exclusively the local structure of this compound throughout its reported morphotropic phase boundary (MPB). Microscopic polarizations due to the cation shifts have been mapped out from the refined crystal structure as a function of composition in order to reveal individual cation behavior driven by the composition. Direct evidences are provided for large static displacements of the cations $\left(\sim 0.2-0.5\AA \right)$, local cation ordering between Ti and Sc, and a categorical change of favored polarization directions of the cations at the conjuncture of the MPB. Apart from Sc, all cations have demonstrated an apparent transition from a relatively defined directional distribution to a broad and random distribution at $x=x_{\mathrm{MPB}}$, suggesting a flattening of the local potential function for them. These features can further be correlated with the general concept of structural instability of a ferroelectric system at the MPB, which is often linked to the manifestation of enhanced physical properties.

A functional renormalization group approach to $d$-dimensional, $N$-component, noncollinear magnets is performed using various truncations of the effective action relevant to study their long distance behavior. With help of these truncations we study the existence of a stable fixed point for dimensions between $d=2.8$ and $d=4$ for various values of $N$ focusing on the critical value $N_c\left(d\right)$ that, for a given dimension $d$, separates a first-order region for $N<N_c\left(d\right)$ from a second-order region for $N>N_c\left(d\right)$. Our approach concludes to the absence of a stable fixed point in the physical—$N=2,3$ and $d=3$—cases, in agreement with the $\epsilon =4-d$ expansion and in contradiction with previous perturbative approaches performed at fixed dimension and with recent approaches based on the conformal bootstrap program.

An efficient density matrix renormalization group (DMRG) algorithm is presented and applied to Y junctions, systems with three arms of $n$ sites that meet at a central site. The accuracy is comparable to DMRG of chains. As in chains, new sites are always bonded to the most recently added sites and the superblock Hamiltonian contains only new or once renormalized operators. Junctions of up to $N=3n+1\approx 500$ sites are studied with antiferromagnetic (AF) Heisenberg exchange $J$ between nearest-neighbor spins $S$ or electron transfer $t$ between nearest neighbors in half-filled Hubbard models. Exchange or electron transfer is exclusively between sites in two sublattices with $N_A\ne N_B$. The ground state (GS) and spin densities ${\rho }_r=\langle S_r^z\rangle$ at site $r$ are quite different for junctions with $S=1/2$, 1, 3/2, and 2. The GS has finite total spin $S_G=2S\left(S\right)$ for even (odd) $N$ and for $M_G=S_G$ in the $S_G$ spin manifold, ${\rho }_r>0(<0)$ at sites of the larger (smaller) sublattice. $S=1/2$ junctions have delocalized states and decreasing spin densities with increasing $N$. $S=1$ junctions have four localized $S_z=1/2$ states at the end of each arm and centered on the junction, consistent with localized states in $S=1$ chains with finite Haldane gap. The GS of $S=3/2$ or 2 junctions of up to 500 spins is a spin density wave with increased amplitude at the ends of arms or near the junction. Quantum fluctuations completely suppress AF order in $S=1/2$ or 1 junctions, as well as in half-filled Hubbard junctions, but reduce rather than suppress AF order in $S=3/2$ or 2 junctions.

The extrinsic dephasing of a hole spin confined to a self-assembled quantum dot is dominated by charge noise acting on an electric-field-dependent $g$-factor. Here we propose the use of the optical Stark effect to reduce the sensitivity of the effective hole Zeeman energy to fluctuations in the local electric field. Calculations using measured quantum dot parameters are presented, and they demonstrate a factor of 10–100 reduction in the extrinsic dephasing. Compared to active stabilization methods, this technique should benefit from reduced experimental complexity.

To elucidate the mechanism of electron transport through atomic point contacts, we investigated the contact-site dependence of electrical conductance on the periodical structure of a moiré pattern observed on a Pb overlayer by scanning tunneling microscopy (STM). In order to eliminate the influence of atomic-site dependence on the conductance, we measured the point contact conductance on sites equivalent in an atomic surface lattice but different in the moiré periodical structure, and found that the conductance does not depend on the contrast of the moiré pattern. The moiré-insensitive conductance indicates a dominant role of local atomic geometry in the point contact conductance. We also revealed that apparent barrier height in the tunneling regime is dependent on the contrast of the moiré pattern, and that the moiré contrast observed by STM on a 7-monolayer thin film originates from the barrier height difference at small bias voltages.

The evolution of a phonon spectrum in a narrow-gap semiconductor FeSi was investigated in a wide range of temperatures (46 K $\le T\le 297$ K, $P=0.1$ MPa) and pressures (0.1 MPa $\le P\le 43$ GPa, $T=297$ K) using nuclear inelastic scattering of synchrotron radiation with the energy resolution 0.53 meV. Decreasing temperature as well as increasing pressure causes a strong reorganization of the phonon spectrum manifested in splitting and shifts of the phonon peaks. The phonon spectra measured under the temperature and pressure conditions corresponding to the same unit cell volume reveal nearly complete matching. On the contrary, the spectra measured under the conditions of the equal mean-square atomic displacements differ drastically. These observations suggest that the transformation of the electronic spectrum of FeSi is controlled predominantly by the change of the unit cell volume. The corresponding changes of the interatomic forces and the resulting modification of the phonon spectrum appear as the direct consequence of this transformation.

Optical illumination on negatively charged nitrogen-vacancy $(\mathrm{N}{\mathrm{V}}^{-})$ centers inevitably causes stochastic charge-state transitions between the $\mathrm{N}{\mathrm{V}}^{-}$ and the neutral charge state of the NV center. It limits the steady-state population of $\mathrm{N}{\mathrm{V}}^{-}$ to 5% at minimum (∼610 nm) and 80% (∼532 nm) at maximum in intrinsic diamond depending on the wavelength. Here, we show Fermi-level control by phosphorus doping generates 99.4 ± 0.1% $\mathrm{N}{\mathrm{V}}^{-}$ under 1-μW and 593-nm excitation which is close to maximum absorption of $\mathrm{N}{\mathrm{V}}^{-}$. The pure $\mathrm{N}{\mathrm{V}}^{-}$ shows a fivefold increase in luminescence and a fourfold enhancement of an optically detected magnetic resonance under 593-nm excitation compared with those in intrinsic diamond.

We present THz range optical conductivity data of a thin film of the near quantum critical heavy-fermion compound ${\mathrm{CeFe}}_2{\mathrm{Ge}}_2$. Our complex conductivity measurements find a deviation from conventional Drude-like transport in a temperature range previously reported to exhibit unconventional behavior. We calculate the frequency-dependent effective mass and scattering rate using an extended Drude model analysis. We find the inelastic scattering rate can be described by a temperature-dependent power law ${\omega }^{n\left(T\right)}$, where $n\left(T\right)$ approaches $\sim 1.0\pm 0.2$ at 1.5 K. This is compared to the $\rho \sim T^{1.5}$ behavior claimed in dc resistivity data and the $\rho \sim T^2$ expected from Fermi-liquid theory. In addition to a low-temperature mass renormalization, we find an anomalous mass renormalization that persists to high temperature. We attribute this to a Hund's coupling in the Fe states in a manner similar to that recently proposed in the ferropnictides. ${\mathrm{CeFe}}_2{\mathrm{Ge}}_2$ appears to be a very interesting system where one may study the interplay between the usual $4f$ lattice Kondo effect and this Hund's enhanced Kondo effect in the $3d$ states.

We theoretically propose how to observe topological effects in a generic classical system of coupled harmonic oscillators, such as classical pendula or lumped-element electric circuits, whose oscillation frequency is modulated fast in time. Making use of Floquet theory in the high-frequency limit, we identify a regime in which the system is accurately described by a Harper-Hofstadter model where the synthetic magnetic field can be externally tuned via the phase of the frequency modulation of the different oscillators. We illustrate how the topologically protected chiral edge states, as well as the Hofstadter butterfly of bulk bands, can be observed in the driven-dissipative steady state under a monochromatic drive. In analogy with the integer quantum Hall effect, we show how the topological Chern numbers of the bands can be extracted from the mean transverse shift of the steady-state oscillation amplitude distribution. Finally, we discuss the regime where the analogy with the Harper-Hofstadter model breaks down.

We introduce and investigate the multiband $d-p$ model describing a ${\mathrm{IrO}}_4$ layer (such as realized in ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$) where all 34 orbitals per unit cell are partly occupied, i.e., $t_{2g}$ and $e_g$ orbitals at iridium and $2p$ orbitals at oxygen ions. The model takes into account anisotropic iridium-oxygen $d-p$ and oxygen-oxygen $p-p$ hopping processes, crystal-field splittings, spin-orbit coupling, and the on-site Coulomb interactions, both at iridium and at oxygen ions. We show that the predictions based on assumed idealized ionic configuration (with $n_0=5+4\times 6=29$ electrons per ${\mathrm{IrO}}_4$ unit) do not explain well the independent ab initio data and the experimental data for ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$. Instead we find that the total electron density in the $d-p$ states is smaller, $n=29-x<n_0$ ($x>0$). When we fix $x=1$, the predictions for the $d-p$ model become more realistic and weakly insulating antiferromagnetic ground state with the moments lying within ${\mathrm{IrO}}_2$ planes along (110) direction is found, in agreement with experiment and ab initio data. We also show that (i) holes delocalize over the oxygen orbitals and the electron density at iridium ions is enhanced; hence (ii) their $e_g$ orbitals are occupied by more than one electron and have to be included in the multiband $d-p$ model describing iridates.

The influence of a small amount of niobium ions (0.6 mol% $\mathrm{N}{\mathrm{b}}_2{\mathrm{O}}_5$) introduced into $\mathrm{PbZr}{\mathrm{O}}_3$ single crystals on the structural, dielectric, optical, and electromechanical properties was studied. The main goal was to search for the influence of this doping on the phase transition sequence. It was found that addition of Nb leads to stabilization of the known intermediate phase and to formation of a new one. It is interesting that locally broken symmetry could be observed both below and far above the Curie temperature. All these results are analyzed in terms of charge compensation phenomena.

The method for three-dimensional imaging with an atomic resolution, based on the measurement of resonant scattering of x rays, is presented and tested on a nanoscale-range occupational ordering of niobium and magnesium ions in the lead magnesium niobate (${\mathrm{PbMg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_3$) single crystal. X-ray diffuse scattering experiments performed at two wavelengths close to the absorption edge of niobium allowed us to record two $1024\times 1024\times 1024$ data sets of scattering intensities covering densely a large volume of the reciprocal space (up to $Q_{\max }=8.5{\AA }^{-1}$, with steps smaller than $\delta Q=0.05{\AA }^{-1}$). It is demonstrated that the anomalous part of the scattering intensity, including both discrete diffraction spots and diffuse scattering, can be employed to reconstruct the local atomic environment around the niobium cation up to the distance of several nanometers.

We study the spin dynamics of a confined chiral soliton lattice whose ends are weakly held. We demonstrate that in this case the system possesses its own resonant frequency. To study features of the resonant dynamics, we analyze the collective motion of the system driven by an oscillating magnetic field directed along the chiral axis. By using the method of collective coordinates we find analytically the resonant frequency and verify the result by numerical simulation of the spin dynamics with the aid of Landau-Lifshitz-Gilbert equations. The numerical simulation shows an appearance of the asymmetric profile of the frequency response function with increasing ac field, which is typical for a nonlinear resonance. To give an explanation of this behavior, we invoke the multiple-time-scale method and predict an emergence of hysteresis phenomena. We also demonstrate that the spin-motive force is strongly amplified by the resonant oscillations.

The magnetic properties of the layered oxypnictide LaMnAsO have been revisited using neutron scattering and magnetization measurements. The present measurements identify the Néel temperature $T_N=360\left(1\right)$ K. Below $T_N$ the critical exponent describing the magnetic order parameter is $\beta =0.33–0.35$, consistent with a three-dimensional Heisenberg model. Above this temperature, diffuse magnetic scattering indicative of short-range magnetic order is observed, and this scattering persists up to $T_{\text{SRO}}=650\left(10\right)$ K. The magnetic susceptibility shows a weak anomaly at $T_{\text{SRO}}$ and no anomaly at $T_N$. Analysis of the diffuse scattering data using a reverse Monte Carlo algorithm indicates that above $T_N$ nearly two-dimensional, short-range magnetic order is present with a correlation length of 9.3(3) Å within the Mn layers at 400 K. The inelastic scattering data reveal a spin gap of 3.5 meV in the long-range ordered state, and strong, low-energy (quasielastic) magnetic excitations emerging in the short-range ordered state. Comparison with other related compounds correlates the distortion of the Mn coordination tetrahedra to the sign of the magnetic exchange along the layer-stacking direction, and suggests that short-range order above $T_N$ is a common feature in the magnetic behavior of layered Mn-based pnictides and oxypnictides.