Despite numerous studies on the atomic structures of Cu-Zr metallic glasses (MGs), their inherent structural ordering, e.g., medium-range order (MRO), remains difficult to describe. Specifically lacking is an understanding of how the MRO responds to deformation and the associated changes in atomic mobility. In this paper, we focus on the impact of deformation on MRO and associated effect on diffusion in a well-relaxed $\mathrm{C}{\mathrm{u}}_{64.5}\mathrm{Z}{\mathrm{r}}_{35.5}$ MG by molecular dynamics simulations. The Cu-Zr MG exhibits a larger elastic limit of 0.035 and a yield stress of 3.5 GPa. The cluster alignment method was employed to characterize the icosahedral short-range order (ISRO) and Bergman-type medium-range order (BMRO) in the models upon loading and unloading. From this analysis, we find the disruption of both ISRO and BMRO occurs as the strain reaches about 0.02, well below the elastic limit. Within the elastic limit, the total fractions of ISRO or BMRO can be fully recovered upon unloading. The diffusivity increases six to eight times in regions undergoing plastic deformation, which is due to the dramatic disruption of the ISRO and BMRO. By mapping the spatial distributions of the mobile atoms, we demonstrate the increase in atomic mobility is due to the extended regions of disrupted ISRO and more importantly BMRO.

Using first-principles density functional theory calculations, we show a semimetal to semiconducting electronic phase transition for bulk ${\mathrm{TiS}}_2$ by applying uniform biaxial tensile strain. This electronic phase transition is triggered by charge transfer from Ti to S, which eventually reduces the overlap between Ti-$\left(d\right)$ and S-$\left(p\right)$ orbitals. The electronic transport calculations show a large anisotropy in electrical conductivity and thermopower, which is due to the difference in the effective masses along the in-plane and out-of-plane directions. Strain-induced opening of band gap together with changes in dispersion of bands lead to threefold enhancement in thermopower for both $p$- and $n$-type ${\mathrm{TiS}}_2$. We further demonstrate that the uniform tensile strain, which enhances the thermoelectric performance, can be achieved by doping ${\mathrm{TiS}}_2$ with larger iso-electronic elements such as Zr or Hf at Ti sites.

The $I\text{−}V$ characteristics of CoFeB/MgO/CoFeB magnetic tunnel junctions show pronounced nonlinearities which are relevant both for sensor applications and for the basic understanding of spin-dependent tunneling. To study the relation between the tunnel characteristics and the tunnel magnetoresistance (TMR) ratio, a series of CoFeB/MgO/CoFeB junctions was annealed with stepwise increasing annealing time at different temperatures. The related TMR ratio and the $I\text{−}V$ characteristics were measured in the temperature range between 15 K and 300 K. This allowed the comparison of $I\text{−}V$ characteristics of the same junction for TMR ratios between 25% and 150% at 300 K thus eliminating the influence of variations in the preparation process of separate individual samples. In addition to a zero bias anomaly observed in particular at low temperatures and for large TMR ratios, a conductance anomaly in the $I\text{−}V$ curves was observed around a bias voltage of 350 mV. A general correlation between the deviation from Ohmic $I\text{−}V$ characteristics and the TMR ratio was found both for parallel and antiparallel magnetizations of both ferromagnetic layers. This means that the shape of the $I\text{−}V$ curves directly scales with the spin polarization of the tunneling current and the proportion of coherent electron tunneling. Both the 350 mV conductance anomaly and the correlation between non-Ohmic characteristics and the TMR ratio can be explained by considering the contributions of the relevant majority and minority spin bands of the ferromagnetic contacts.

The effect of strong disorder on chiral-symmetric three-dimensional lattice models is investigated via analytical and numerical methods. The phase diagrams of the models are computed using the noncommutative winding number, as functions of disorder strength and model's parameters. The localized/delocalized characteristic of the quantum states is probed with level statistics analysis. Our study reconfirms the accurate quantization of the noncommutative winding number in the presence of strong disorder, and its effectiveness as a numerical tool. Extended bulk states are detected above and below the Fermi level, which are observed to undergo the so-called “levitation and pair annihilation” process when the system is driven through a topological transition. This suggests that the bulk invariant is carried by these extended states, in stark contrast with the one-dimensional case where the extended states are completely absent and the bulk invariant is carried by the localized states.

Transport coefficients, the elements of the so-called Onsager matrix, are required for accurate mesoscopic simulations of kinetics or to predict macroscopic diffusion kinetic behavior. These coefficients can be significantly affected by strain. At the atomic scale, the effect of strain on atomic jump frequencies can be computed using density functional theory calculations. The present work shows how these results can be used to compute the strain-dependent Onsager matrix. Using an analytical method—the self-consistent mean field method—we compute analytical expressions of the Onsager matrix describing vacancy-mediated diffusion of impurities in face-centered cubic structures under elementary strains. Also, we compute the derivatives of the Onsager matrix with respect to strain—the elasto-diffusion tensor—to investigate strain sensitivity of transport. We show that the atomic scale symmetry breaking induced by strain changes diffusion behavior qualitatively. This phenomenon is shown for the Ni(Si) alloy under tetragonal strain. The terms of the Onsager matrix are found to be non-Arrhenian, as well as their derivative with respect to strain. In this case, nonlinear effects leading to a solute drag reduction are identified.

We present a systematic study of the spin transport properties in two different bilayer systems, ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Ru}$ and ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Ta}$, combining ferromagnetic resonance (FMR) and inverse spin Hall effect (ISHE) voltage measurements. We have estimated the effective spin mixing conductance $g^{\uparrow \downarrow }$ by analyzing the permalloy (Py) thickness dependence of the FMR linewidth obtaining $g^{\uparrow \downarrow }=(3.8\pm 0.7)\times {10}^{15}{\mathrm{cm}}^{-2}$ and $g^{\uparrow \downarrow }=(1.3\pm 0.4)\times {10}^{15}{\mathrm{cm}}^{-2}$ for Py/Ru and Py/Ta, respectively. Analyzing the Ta thickness dependence of the ISHE voltage, we have been able to extract the spin diffusion length, ${\lambda }_{SD}=1.5\pm 0.5$ nm, and spin Hall angle, ${\Theta }_{SH}=-0.03\pm 0.01$, of Ta. From the two series of Py/Ta bilayers—with thickness variation of ferromagnetic and nonmagnetic layers, respectively—we demonstrate a path to estimate the spin diffusion length from the experimental data, independent of the spin Hall angle and the microwave field amplitude.

We report high-field magnetization, electron spin resonance (ESR), and Raman scattering measurements of the coupled spin-tetrahedra system ${\mathrm{Cu}}_4{\mathrm{Te}}_5{\mathrm{O}}_{12}{\mathrm{Cl}}_4$ with magnetic ordering at $T_N=13.6$ K. We find thermodynamic and spectroscopic signatures for the concomitant occurrence of localized and collective magnetism. Magnetization measurements up to 60 T exhibit a spin-flop transition at ${\mu }_0{H}_{\mathrm{SF}}=16$ T only for $H\parallel c$ as well as periodic magnetization steps at ${\mu }_{0}H=16.5,24.8,33.8,42.3,\text{and}49.7$ T, which are independent of the crystallographic orientations. For $T>T_N$, the temperature dependence of ESR linewidth is described by a critical power law, $\Delta B_{pp}\left(T\right)\propto {(T-T_N)}^{-0.56\pm 0.02}$. For $T<T_N$, an antiferromagnetic resonance mode is observed for $H\parallel c$, and its linewidth is given by $\Delta B_{pp}\left(T\right)\propto T^{3.13\pm 0.04}$, being close to $T^4$ expected for a classical magnet. Raman spectra show three one-magnon-like excitations superimposed on a broad two-magnon continuum. While the two higher frequency modes show an intensity variation in accordance to a three-dimensional Heisenberg antiferromagnet, the lower frequency mode clearly deviates. These results suggest that ${\mathrm{Cu}}_4{\mathrm{Te}}_5{\mathrm{O}}_{12}{\mathrm{Cl}}_4$ is a unique material which shows a dual character of zero-dimensional, localized and three-dimensional, collective magnetic behaviors.

We prove numerically and by dualities the existence of modulated, commensurate and incommensurate states of topological quantum matter in systems of parafermions, motivated by recent proposals for the realization of such systems in mesoscopic arrays. In two space dimensions, we obtain the simplest representative of a topological universality class that we call Lifshitz. It is characterized by a topological tricritical point where a nonlocally ordered homogeneous phase meets a disordered phase and a third phase that displays modulations of a nonlocal order parameter.

We study the extent of the spin liquid phases in the Kitaev-Heisenberg model using infinite projected entangled-pair states tensor network ansatz wave functions directly in the thermodynamic limit. To assess the accuracy of the ansatz wave functions, we perform benchmarks against exact results for the Kitaev model and find very good agreement for various observables. In the case of the Kitaev-Heisenberg model, we confirm the existence of six different phases: Néel, stripy, ferromagnetic, zigzag, and two spin liquid phases. We find finite extents for both spin liquid phases and discontinuous phase transitions connecting them to symmetry-broken phases.

We report on a detailed low-energy electron diffraction (LEED) and low-temperature scanning tunneling microscopy (STM) study of the intermetallic surface compound ${\mathrm{CePt}}_5$ on Pt(111). Depending on the thickness we observe various diffraction patterns and superstructures. In the low-thickness regime a slightly compressed $(2\times 2)$ superstructure is aligned along the $\langle 1\overline{1}0\rangle$ direction of the Pt(111) substrate. STM reveals another, much larger superstructure with a periodicity of ($9.02\pm 0.45$) nm presumably responsible for the strongly broadened LEED spots. At about 3 unit cells (u.c.) the surface is dominated by a $(3\sqrt{3}\times 3\sqrt{3})R{30}^{\circ }$ pattern as revealed by LEED satellites and Fourier-transformed high-resolution STM images. It is interpreted as a moiré pattern between the film and the substrate. We precisely determine the superstructure of the intermetallic film to $(\frac{10}{9}\sqrt{3}\times \frac{10}{9}\sqrt{3})R{30}^{\circ }$ with respect to the Pt(111) substrate. Above 3 u.c. the satellites progressively disappear. A model is developed that consistently describes this thickness-dependent transition. For ${\mathrm{CePt}}_5$ films with a thickness between 6 and 11 u.c. the lattice of the compressed $(2\times 2)$ superstructure rotates back into the substrate's $\langle 1\overline{1}0\rangle$ directions.

Planar metallic nanoparticles separated by nanoscale distances from a metal film support unique plasmonic resonances useful for controlling a wide range of photodynamic processes. The fundamental resonance of a film-coupled planar nanoparticle arises from a transmission-line mode localized between nanoparticle and film, whose properties can be roughly approximated by closed form expressions similar to those used in patch antenna theory. The insight provided by the analytical expressions, and the potential of achieving similar closed-form expressions for a range of plasmonic phenomenon such as spasing, fluorescence enhancement, and perfect absorbers, motivates a more detailed study of the film-coupled patch. Here, we present an expanded analytical analysis of the plasmonic patch geometry, applying an eigenmode expansion method to arrive at a more accurate description of the field distribution underneath a film-coupled plasmonic nanocube. The fields corresponding to the inhomogeneous Maxwell's equations are expanded in a set of lossless waveguide eigenmodes. Radiation damping and Ohmic losses are then perturbatively taken into account by considering an equivalent surface impedance. We find that radiative loss couples the lossless eigenmodes, leading to discernible features in the scattering spectra of the nanocubes. The method presented can be further applied to the case of point source excitations, in which accounting for all potential eigenmodes becomes essential.

We study the emergence of strongly correlated states and Kondo physics in disordered graphene. Diluted short-range disorder gives rise to localized midgap states at the vicinity of the system charge neutrality point. We show that long-range disorder, ubiquitous in graphene, allows for the coupling of these localized states to an effective (disorder averaged) metallic band. The system is described by an Anderson-like model. We use the numerical renormalization group method to study the distributions of Kondo temperatures $P\left(T_K\right)$. The results show that disorder can lead to long logarithmic tails in $P\left(T_K\right)$, consistent with a quantum Griffiths phase.

We report on nonlinear transport measurements in a GaAs/AlGaAs quantum well exhibiting a colossal negative magnetoresistance effect. Under applied dc bias, the magnetoresistance becomes nonmonotonic, exhibiting distinct extrema that move to higher magnetic fields with increasing current. In the range of magnetic fields corresponding to the resistivity minimum at zero bias, the resistivity increases linearly with current and the rate of this increase scales with the inverse magnetic field. The latter observation is consistent with the theory, proposed more than 35 years ago, considering classical memory effects in the presence of strong, dilute scatterers.

Resonant photoelastic coupling opens new perspectives for strongly enhanced light-sound interaction in semiconductor optomechanical resonators. One potential problem, however, is the reduction of the cavity $Q$ factor induced by dissipation when the resonance is approached. We show in this Rapid Communication through Raman-scattering experiments that cavity-polariton mediation in the light-matter process overcomes this limitation allowing for a strongly enhanced photon-phonon coupling without significant lifetime reduction in the strong-coupling regime. Huge optomechanical coupling factors in the petaHz/nm range are envisaged, three orders of magnitude larger than the backaction produced by the mechanical displacement of the cavity mirrors.

A metallic system without any further doping was obtained combining, in a bulk film, heterojunctions made by subsequent depositions of ${\mathrm{C}}_{60}$ and picene layers on Ag(111). This is caused by the formed dipole between the two molecules due to the huge difference in electron affinities and the charge transfer from the substrate. The above situation and the expected molecular geometry have also a role when the heterojunction film is doped with potassium. ${\mathrm{C}}_{60}$ phases diverse from those observed in bulk ${\mathrm{C}}_{60}$, especially, a metallic state with continuous alkali doping of the LUMO bands was found. This opens the way towards novel bulk molecular heterojunction structures that may create new electronic phases in strongly correlated molecular materials. The present case appears as the only manner known so far to form a bulk metallic ${\mathrm{K}}_x{\mathrm{C}}_{60}$ system ($0<x<6$) that may evoke the possibility of seeing the awaited dome-shaped region of the doping-temperature phase diagram if the system should show superconductivity.

The recent discoveries of both chemical-driven and strain-driven morphotropic phase boundaries (MPBs) in $\mathrm{BiFe}{\mathrm{O}}_3$ (BFO) thin films have opened up new horizons in developing high-performance lead-free piezoelectrics. An attempt to bridge these two MPBs is made by doping La into highly strained BFO thin films with the coexistence of tetragonal-like and rhombohedral-like phases. The structural, morphological, and ferroelectric properties of such films are investigated. It is observed that La doping changes the energy landscape between the tetragonal-like and the rhombohedral-like polymorphs due to the chemical pressure imposed by the La substitution. Polar instability is found upon increasing La doping for the in-plane polarization component, which correlates with the vanishing of in-plane ferroelectric domain structures. The transition sequence of the in-plane ferroelectric polarization resembles that previously reported for the bulklike rhombohedral phase of BFO under continuous La doping, indicating the universality of the chemical-alloying effect on the ferroelectric order.

Polarized-neutron-diffraction (PND) measurements were carried out using a pseudo-single-phase powder sample of ferromagnetic ${\alpha }^{\prime \prime }\text{−}{\mathrm{Fe}}_{16}{\mathrm{N}}_2$ nanoparticles. For the well-identified ${\alpha }^{\prime \prime }\text{−}{\mathrm{Fe}}_{16}{\mathrm{N}}_2$ phase, sizes of the magnetic moments at the three crystallographic Fe sites were determined in the absolute scale. The agreement between the magnetization value deduced from the present PND and that measured by a magnetometer $\left(M_{\mathrm{VSM}}\right)$ supports the hypothesis that $M_{\mathrm{VSM}}$ is primarily caused by the magnetization value in the target ${\alpha }^{\prime \prime }\text{−}{\mathrm{Fe}}_{16}{\mathrm{N}}_2$; thus there is no evidence for macroscopic giant saturation magnetization, at least for ${\alpha }^{\prime \prime }\text{−}{\mathrm{Fe}}_{16}{\mathrm{N}}_2$ nanoparticles. On the basis of the large magnetic moment size at one of the Fe sites, a possible coexisting state of localized spins and itinerant electron spins is inferred. Drawing a distinction between thin films and nanoparticles is currently necessary because of their divergent magnetic evolutions.

We propose a simple method of calculating inhomogeneous, atomic-scale phenomena in superconductors which makes use of the wave function information traditionally discarded in the construction of tight-binding models used in the Bogoliubov–de Gennes equations. The method uses symmetry-based first-principles Wannier functions to visualize the effects of superconducting pairing on the distribution of electronic states over atoms within a crystal unit cell. Local symmetries lower than the global lattice symmetry can thus be exhibited as well, rendering theoretical comparisons with scanning tunneling spectroscopy data much more useful. As a simple example, we discuss the geometric dimer states observed near defects in superconducting FeSe.