Inelastic neutron scattering measurements on silver oxide (${\text{Ag}}_2\text{O}$) with the cuprite structure were performed at temperatures from 40 to 400 K, and Fourier transform far-infrared spectra were measured from 100 to 300 K. The measured phonon densities of states and the infrared spectra showed unusually large energy shifts with temperature, and large linewidth broadenings. First principles molecular dynamics (MD) calculations were performed at various temperatures, successfully accounting for the negative thermal expansion (NTE) and local dynamics. Using the Fourier-transformed velocity autocorrelation method, the MD calculations reproduced the large anharmonic effects of ${\text{Ag}}_2\text{O}$, and were in excellent agreement with the neutron scattering data. The quasiharmonic approximation (QHA) was less successful in accounting for much of the phonon behavior. The QHA could account for some of the NTE below 250 K, although not at higher temperatures. Strong anharmonic effects were found for both phonons and for the NTE. The lifetime broadenings of ${\text{Ag}}_2\text{O}$ were explained by anharmonic perturbation theory, which showed rich interactions between the Ag-dominated modes and the O-dominated modes in both up- and down-conversion processes.

We use Monte Carlo simulations to demonstrate generic scaling aspects of classical phase transitions approached through a quench (or annealing) protocol where the temperature changes as a function of time with velocity $v$. Using a generalized Kibble-Zurek ansatz, we demonstrate dynamic scaling for different types of stochastic dynamics (Metropolis, Swendsen-Wang, and Wolff) on Ising models in two and higher dimensions. We show that there are dual scaling functions governing the dynamic scaling, which together describe the scaling behavior in the entire velocity range $v\in [0,\infty )$. These functions have asymptotics corresponding to the adiabatic and diabatic limits, and close to these limits they are perturbative in $v$ and $1/v$, respectively. Away from their perturbative domains, both functions cross over into the same universal power-law scaling form governed by the static and dynamic critical exponents (as well as an exponent characterizing the quench protocol). As a by-product of the scaling studies, we obtain high-precision estimates of the dynamic exponent $z$ for the two-dimensional Ising model subject to the three variants of Monte Carlo dynamics: for single-spin Metropolis updates $z_{\mathrm{M}}=2.1767\left(5\right)$, for Swendsen-Wang multicluster updates $z_{\mathrm{SW}}=0.297\left(3\right)$, and for Wolff single-cluster updates $z_{\text{W}}=0.30\left(2\right)$. For Wolff dynamics, we find an interesting behavior with a nonanalytic breakdown of the quasiadiabatic and diabatic scalings, instead of the generic smooth crossover described by a power law. We interpret this disconnect between the two scaling regimes as a dynamic phase transition of the Wolff algorithm, caused by an effective sudden loss of ergodicity at high velocity.

The paper presents an inelastic neutron scattering study of lattice dynamics of the NaI alkali halide crystal, aimed to check the previously reported signatures of intrinsic localized modes, so-called discrete breathers. It is shown that three unusual spectral features, previously interpreted as an evidence for thermally induced discrete breathers (an anomalous spectral band in the phononic gap, longitudinal acoustic ${\Lambda }_1$ phonon branch overbending, and fragmentation of the $X$-point transverse optic mode response) are all absent in the independent experiments reported here.

By utilizing tensor-network-based methods, we investigate the zero- and finite-temperature properties of the spin-1/2 Heisenberg antiferromagnetic (HAF) model on an infinite Husimi lattice that contains 3/2 sites per triangle. The ground state of this model is found to possess vanishing local magnetization and is featureless; the spin-spin and dimer-dimer correlation functions are verified to decay exponentially, and its ground-state energy per site is determined to be $e_0=-0.4343\left(1\right)$, which is very close to that [$e_0=-0.4386\left(5\right)$] of the intriguing kagome HAF model. The magnetization curve shows the absence of a zero-magnetization plateau, implying a gapless excitation. A $1/3$-magnetization plateau with spin-up-up-down state is observed, which is selected and stabilized by quantum fluctuations. A ground-state phase diagram under magnetic fields is presented. Moreover, both magnetic susceptibility and the specific heat are studied, whose low-temperature behaviors reinforce the conclusion that the HAF model on the infinite Husimi lattice owns a gapless and featureless spin-liquid ground state.

We have prepared oxygen isotope exchanged crystals of impurity-free ${\text{YBa}}_2$${\text{Cu}}_3$${\text{O}}_y$ with various oxygen contents, and examined pure doping ($p$) dependence of isotope effect on superconducting transition temperature. With decreasing oxygen contents, the isotope exponent $\alpha$ monotonously increases without any anomaly around $p=1/8$. The monotonous increase in $\alpha$ indicates that phonons are involved in the mechanism which causes the monotonous $T_c$ suppression with underdoping.

We report crystal structure, electronic structure, and magnetism of manganese tetraboride, ${\text{MnB}}_4$, synthesized under high-pressure, high-temperature conditions. In contrast to superconducting ${\text{FeB}}_4$ and metallic ${\text{CrB}}_4$, which are both orthorhombic, ${\text{MnB}}_4$ features a monoclinic crystal structure. Its lower symmetry originates from a Peierls distortion of the Mn chains. This distortion nearly opens the gap at the Fermi level, but despite the strong dimerization and the proximity of ${\text{MnB}}_4$ to the insulating state, we find indications for a sizable paramagnetic effective moment of about 1.7 μ${}_B$/f.u., ferromagnetic spin correlations, and, even more surprisingly, a prominent electronic contribution to the specific heat. However, no magnetic order has been observed in standard thermodynamic measurements down to 2 K. Altogether, this renders ${\text{MnB}}_4$ a structurally simple but microscopically enigmatic material; we argue that its properties may be influenced by electronic correlations.

Density functional/molecular dynamics simulations and experimental data (x-ray and neutron diffraction, extended x-ray absorption fine structure) have been combined to determine structural and other properties of amorphous ${\text{AsS}}_2$ and $\text{Ag}{\text{AsS}}_2$. These semiconductors represent the two small regions of the Ag-As-S ternary diagram where homogeneous glasses form, and they have quite different properties, including ionic conductivities. We find excellent agreement between the experimental results and large-scale (over 500 atoms) simulations, and we compare and contrast the structures of ${\text{AsS}}_2$ and $\text{Ag}{\text{AsS}}_2$. The calculated electronic structures, vibrational densities of states, ionic mobilities, and cavity distributions of the amorphous materials are discussed and compared with data on crystalline phases where available. The high mobility of Ag in solid state electrolyte applications is coupled to the large cavity volume in ${\text{AsS}}_2$ and local modifications of the covalent As-S network in the presence of Ag.

Thermal transport in a metallic multilayer on picosecond time scales is controlled by the electronic thermal conductivity (${\Lambda }_e$), the electronic interfacial thermal conductance ($G_{ee}$), and electron-phonon coupling constant ($g$). We analyze heat transfer in a nanoscale Pt/Au bilayer using data obtained in pump-probe measurements and modeling using a transmission-line-equivalent circuit. For optical exciation of either the Pt or Au side of the bilayer, the majority of energy is deposited into the Pt phonons on a time scale of ≈1 ps because $g_{\mathrm{Pt}}\gg g_{\mathrm{Au}}$ and $G_{ee}>g_{\mathrm{Au}}{h}_{\mathrm{Au}}$, where $h_{\mathrm{Au}}$ is the thickness of the Au layer. We determine $g$ of the Au layer and set a lower bound on $G_{ee}$ of the Pt/Au interface: $g_{\mathrm{Au}}$ = 2.2 ± 0.6 × 10${}^{16}$ W m${}^{-3}$ K${}^{-1}$ and $G_{ee}$ > 5 GW m${}^{-2}$ K${}^{-1}$.

Many future concepts for spintronic devices are based on the current-driven motion of magnetic domain walls through nanowires. Consequently a thorough understanding of the domain wall mobility is required. However, the magnitude of the nonadiabatic component of the spin-transfer torque driving the domain wall is still debated today as various experimental methods give rise to a large range of values for the degree of nonadiabaticity. Strikingly, experiments based on vortex domain wall motion in magnetic nanowires consistently result in lower values compared to other methods. Based on the micromagnetic simulations presented in this contribution we can attribute this discrepancy to the influence of distributed disorder which vastly affects the vortex domain wall mobility, but is most often not taken into account in the models adopted to extract the degree of nonadiabaticity.

For the two-dimensional $Q$-state Potts model at criticality, we consider Fortuin-Kasteleyn and spin clusters and study the average number $N_{\Gamma }$ of clusters that intersect a given contour $\Gamma$. To leading order, $N_{\Gamma }$ is proportional to the length of the curve. Additionally, however, there occur logarithmic contributions related to the corners of $\Gamma$. These are found to be universal and their size can be calculated employing techniques from conformal field theory. For the Fortuin-Kasteleyn clusters relevant to the thermal phase transition, we find agreement with these predictions from large-scale numerical simulations. For the spin clusters, on the other hand, the cluster numbers are not found to be consistent with the values obtained by analytic continuation, as conventionally assumed.

High-quality K(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ single crystals have been grown by using the KAs flux method. Instead of increasing the superconducting transition temperature $T_{\mathrm{c}}$ through electron doping, we find that Co impurities rapidly suppress $T_{\mathrm{c}}$ down to zero at only $x\approx$ 0.04. Such an effective suppression of $T_{\mathrm{c}}$ by impurities is quite different from that observed in Ba${}_{0.5}$K${}_{0.5}$Fe${}_2$As${}_2$ with multiple nodeless superconducting gaps. Thermal conductivity measurements in zero field show that the residual linear term ${\kappa }_0/T$ only changes slightly with 3.4% Co doping, despite the sharp increase in the scattering rate. The implications of these anomalous impurity effects are discussed.

The metal-nonmetal transition in Ce- and Rh-substituted ${\text{PrRu}}_4$${\text{P}}_{12}$ was investigated through magnetic susceptibility, x-ray superlattice reflection, and inelastic neutron scattering (INS) measurements. The saturation in the magnetic susceptibility at low temperatures suggests a singlet ground state for Pr sites in both compounds. This finding is in contrast to the staggered order of singlet and triplet ground states found in the ordered phase of ${\text{PrRu}}_4$${\text{P}}_{12}$, which leads to a diverging susceptibility. The intensities of x-ray superlattice reflections of both compounds develop below 45 K and decrease rapidly below 10 K with a simultaneous decrease in electrical resistivity. INS experiments reveal that 4$f$ electron states in both compounds change drastically from two distinct crystal field (CF) level schemes corresponding to an order parameter in the multipole ordered phase (10 $\text{K}<T<45$ K) to a nearly uniform CF level scheme below 10 K. The uniform CF ground state at the Pr sites carries no degree of freedom relevant to the staggered ordering pattern and electronic gap formation. Therefore, the substituted systems exhibit a reentrant metallic state at the lowest temperature. These phenomena may originate from effective electron doping due to atomic substitution.

We investigate the basic quantum-mechanical processes behind the nonproportional response of scintillators to incident radiation responsible for reduced resolution. For this purpose, we conduct a comparative first-principles study of quasiparticle spectra on the basis of the $G_0{W}_0$ approximation as well as absorption spectra and excitonic properties by solving the Bethe-Salpeter equation for two important systems, NaI and ${\mathrm{SrI}}_2$. The former is a standard scintillator material with well-documented nonproportionality, while the latter has recently been found to exhibit a very proportional response. We predict band gaps for NaI and ${\mathrm{SrI}}_2$ of 5.5 and 5.2 eV, respectively, in good agreement with experiment. Furthermore, we obtain binding energies for the ground state excitons of 216 meV for NaI and $195\pm 25\text{meV}$ for ${\mathrm{SrI}}_2$. We analyze the degree of exciton anisotropy and spatial extent by means of a coarse-grained electron-hole pair-correlation function. Thereby, it is shown that the excitons in NaI differ strongly from those in ${\mathrm{SrI}}_2$ in terms of structure and symmetry, even if their binding energies are similar. Furthermore, we show that quite unexpectedly the spatial extents of the highly-anisotropic low-energy excitons in ${\mathrm{SrI}}_2$ in fact exceed those in NaI by a factor of two to three in terms of the full width at half maxima of the electron-hole pair-correlation function.

For a series of samples with two-dimensional electron systems in dilute ${\text{Al}}_x$${\text{Ga}}_{1-x}$As, with varying $x$ from $0\%$ to $0.85\%$, we survey the pinning mode resonances of Wigner solids at the low Landau filling termination of the fractional quantum Hall effect series. For all $x$ studied, the pinning modes are present with frequencies $f_{\mathrm{pk}}$ that are consistent with collective weak pinning. For $x\ge 0.22\%$ we find $f_{\mathrm{pk}}$ vs $B$ exhibits a rapid increase that is not present for $x=0$. We find the observed $f_{\mathrm{pk}}$ is much smaller than values calculated with a simple Wigner solid model which neglects the effects of the disorder on the charge distribution of a carrier.

We present the photoluminescence excitation study of the self-assembled CdTe/ZnTe quantum dots doped with manganese ions. We demonstrate the identification method of spontaneously coupled quantum dots pairs containing single ${\text{Mn}}^{2+}$ ions. As the result of the coupling, the resonant absorption of the photon in one quantum dot is followed by the exciton transfer into a neighboring dot. It is shown that the ${\text{Mn}}^{2+}$ ion might be present in the absorbing, emitting, or both quantum dots. The magnetic properties of the ${\text{Mn}}^{2+}$ spin are revealed by a characteristic sixfold splitting of the excitonic line. The statistics of the value of this splitting is analyzed for the large number of the dots and gives the information on the maximum density of the neutral exciton wave function.

We experimentally investigate electron transport through the interface between a permalloy ferromagnet and the edge of a two-dimensional electron system with strong Rashba-type spin-orbit coupling. We observe strongly nonlinear transport around zero bias at milli-Kelvin temperatures. The observed nonlinearity is fully suppressed above some critical values of temperature, magnetic field, and current through the interface. We interpret this behavior as the result of spin accumulation at the interface and its current-induced absorption as a magnetization torque.

Previously unknown phenomena, scale, and kinetic effects are revealed by introducing the finite width ${\Delta }_{\xi }$ of the particle-exterior interface as the additional scale parameter and thermally activated melting in the phase field approach. In addition to traditional continuous barrierless premelting and melting for ${\Delta }_{\xi }=$ 0, barrierless hysteretic jumplike premelting (melting) and thermally activated premelting (melting) via critical nucleus are revealed. A very rich temperature $\theta \text{−}{\Delta }_{\xi }$ transformation diagram is found, which includes various barrierless and thermally activated transformations between solid, melt, and surface melt, and complex hysteretic behavior under various temperature and ${\Delta }_{\xi }$ trajectories. Bistable states (i.e., spontaneous thermally activated switching between two states) between solid and melt or surface melt are found for Al particles. Strong dependence of the melting temperature (which, in contrast to previous approaches, is defined for thermally activated premelting and melting) for nanoparticles of various radii on ${\Delta }_{\xi }$ is found. Results are in good agreement with experiments for Al for ${\Delta }_{\xi }=0.8–1.2$nm. They open an unexplored direction of controlling surface melting and melting or solidification by controlling the width of the external surface and utilizing predicted phenomena. They also can be expanded for other phase transformations (e.g., amorphization, solid-solid diffusionless, diffusive, and electromagnetic transformations) and phenomena, imbedded particles, and mechanical effects.

Tunneling spectroscopy of a Nb coupled carbon nanotube quantum dot reveals the formation of pairs of Andreev bound states (ABS) within the superconducting gap. A weak replica of the lower ABS is found, which is generated by quasiparticle tunneling from the ABS to the Al tunnel probe. An inversion of the ABS dispersion is observed at elevated temperatures, which signals the thermal occupation of the upper ABS. Our experimental findings are well supported by model calculations based on the superconducting Anderson model.

We study the signatures of disorder in the production of orbital electron entanglement in quantum wires. Disordered entanglers suffer the effects of localization of the electron wave function and random fluctuations in entanglement production. This manifests in the statistics of the concurrence, a measure of the produced two-qubit entanglement. We calculate the concurrence distribution as a function of the disorder strength within a random-matrix approach. We also identify significant constraints on the entanglement production as a consequence of the breaking/preservation of time-reversal symmetry. Additionally, our theoretical results are independently supported by simulations of disordered quantum wires based on a tight-binding model.