We investigate the entanglement and the Rényi entropies of two electronic leads connected by a quantum point contact. For noninteracting electrons, the entropies can be related to the cumulants of the full counting statistics of transferred charge which in principle are measurable. We consider the entanglement entropy generated by operating the quantum point contact as a quantum switch which is opened and closed in a periodic manner. Using a numerically exact approach we analyze the conditions under which a logarithmic growth of the entanglement entropy predicted by conformal field theory should be observable in an electronic conductor. In addition, we consider clean single-particle excitations on top of the Fermi sea (levitons) generated by applying designed pulses to the leads. We identify a Hong-Ou-Mandel-like suppression of the entanglement entropy by interfering two levitons on a quantum point contact tuned to half transmission.

We present a detailed mechanism of, and the effect of homogeneous strains on, the migration of uranium vacancies in ${\mathrm{UO}}_2$. Vacancy migration pathways and barriers are identified using density functional theory and the effect of uniform strain fields are accounted for using the dipole tensor approach. We report complex migration pathways and noncubic symmetry associated with the uranium vacancy in ${\mathrm{UO}}_2$ and show that these complexities need to be carefully accounted for to predict the correct diffusion behavior of uranium vacancies. We show that under homogeneous strain fields, only the dipole tensor of the saddle with respect to the minimum is required to correctly predict the change in the energy barrier between the strained and the unstrained case. Diffusivities are computed using kinetic Monte Carlo simulations for both neutral and fully charged state of uranium single and divacancies. We calculate the effect of strain on migration barriers in the temperature range 800–1800 K for both vacancy types. Homogeneous strains as small as $2\%$ have a considerable effect on diffusivity of both single and divacancies of uranium, with the effect of strain being more pronounced for single vacancies than divacancies. In contrast, the response of a given defect to strain is less sensitive to changes in the charge state of the defect. Further, strain leads to anisotropies in the mobility of the vacancy and the degree of anisotropy is very sensitive to the nature of the applied strain field for strain of equal magnitude. Our results suggest that the influence of strain on vacancy diffusivity will be significantly greater when single vacancies dominate the defect structure, such as sintering, while the effects will be much less substantial under irradiation conditions where divacancies dominate.

This paper summarizes 0 to 0.6 GPa neutron diffraction measurements of a nickel hexacyanochromate coordination polymer (NiCrPB) that has the face-centered-cubic, Prussian blue structure. Deuterated powders of NiCrPB contain $\approx 100$-nm-sided cubic particles. The application of a large magnetic field shows the ambient-pressure, saturated magnetic structure. Pressures of less than 1 GPa have previously been shown to decrease the magnetic susceptibility by as much as half, and we find modifications to the nuclear crystal structure at these pressures that we quantify. Bridging cyanide molecules isomerize their coordination direction under pressure to change the local ligand field and introduce inhomogeneities in the local (magnetic) anisotropy that act as pinning sites for magnetic domains, thereby reducing the low-field magnetic susceptibility.

We present neutron scattering measurements of the phonon-roton and layer modes of liquid helium films adsorbed in 25-Å pore diameter gelsil as a function of temperature. The goal is to determine whether the well-defined phonon-roton and layer modes observed at low temperature at partial fillings of the porous media persist as well-defined modes at higher temperatures above the superfluid phase, as is the case of fully filled pores (3D liquid). We find that well defined P-R modes exist in films at temperatures well above the superfluid phase. This is the case at all fillings investigated. Liquid ${}^4\mathrm{He}$ in porous media is an example of a Bose liquid in disorder. The existence of P-R modes above $T_c$ suggests the existence of patches or islands of Bose condensed liquid that have order [localized Bose-Einstein condensation (LBEC)] above $T_c$. The interpretation is that the well-defined P-R modes propagate in the patches of BEC. Gelsil partially filled with liquid helium shows the same LBEC behavior as found previously in fully filled gelsil (as in a 3D liquid).

In this paper we study the growth properties of domains of low-spin molecules in a high-spin background in open-boundary elliptically shaped spin-crossover systems within the framework of a mechanoelastic model. The molecules are situated on a triangular lattice and are linked by springs, through which they interact. Elliptical shapes are chosen in order to allow an in-depth analysis of cluster shapes as a function of the local curvature at their starting point and the length of the interface between the two phases. In contrast to the case of rectangular and hexagonal shapes, where the clusters always start from corners, we find that for ellipses clusters nucleate from vertices, covertices, or any other site. We apply and compare two kinds of dynamics, Eden-like and Kawasaki, in order to determine the stable shape of the clusters and the most probable starting points. We show that the wetting angle for small clusters is somewhat higher than $\pi /2$ and approaches this value only for large clusters. The stability of clusters is analyzed by comparing the Gibbs free energy to the elastic energy in the system and is discussed as a function of the cluster size, curvature of the starting place, and temperature.

Flexoelectricity is a universal property of all dielectrics by which they generate a voltage in response to an inhomogeneous deformation. One of the controversial issues in this field concerns the magnitude of flexoelectric coefficients measured experimentally, which greatly exceed theoretical estimates. Furthermore, there is a broad scatter amongst experimental measurements. The truncated pyramid compression method is one of the common setups to quantify flexoelectricity, the interpretation of which relies on simplified analytical equations to estimate strain gradients. However, the deformation fields in three-dimensional pyramid configurations are highly complex, particularly around its edges. In the present work, using three-dimensional self-consistent simulations of flexoelectricity, we show that the simplified analytical estimations of strain gradients in compressed pyramids significantly overestimate flexoelectric coefficients, thus providing a possible explanation to reconcile different estimates. In fact, the interpretation of pyramid compression experiments is highly nontrivial. We systematically characterize the magnitude of this overestimation, of over one order of magnitude, as a function of the truncated pyramid configuration. These results are important to properly characterize flexoelectricity, and provide design guidelines for effective electromechanical transducers exploiting flexoelectricity.

We study the temperature behaviors of the Hall coefficient, $R_H$, and longitudinal conductivity, $\sigma$, of two series of ${\mathrm{Ag}}_x\left({\mathrm{SnO}}_2\right){}_{1-x}$ $(x$ being the Ag volume fraction) granular films lying in the metallic regime. The first (second) series of films are $\sim 500$ $(\sim 9)$ nm thick and constitute a three- (two-) dimensional granular array. In the high-$x$ regime with $g_T\gg g_T^c$ $(g_T$ being the dimensionless intergrain tunneling conductance, and $g_T^c$ being the critical tunneling conductance at the percolation threshold), we observe a $R_H\propto lnT$ law from $\sim 6$ to 300 K. This $lnT$ behavior is independent of array dimensionality. We also observe a $\sigma \propto lnT$ law in the temperature range $\sim 20$–100 K. Below $\sim 10$ K, the temperature behavior of $\sigma$ changes to a $\sqrt{T}$ dependence in thick films, while it changes to a different $lnT$ dependence in thin films. The overall $R_H$ and $\sigma$ characteristics can be explained by the electron-electron interaction (EEI) effects in the presence of granularity. As $x$ is reduced and approaches the percolation threshold, we found that the $lnT$ dependences of $R_H$ and $\sigma$ still hold for a wide temperature range. We propose an explanation for the long-standing puzzle of the $\sigma \propto lnT$ dependence, which has previously been frequently observed in composite systems near the quantum percolation threshold, as arising from the same EEI effect considered in the recent theory of granular metals.

The $5d$ iridates have been the subject of much recent attention due to the predictions of a large array of novel electronic phases driven by twisting strong spin-orbit coupling and Hubbard correlation. As a prototype, the single-layered perovskite $\mathrm{S}{\mathrm{r}}_2\mathrm{Ir}{\mathrm{O}}_4$ was first revealed to host a $J_{\mathrm{eff}}=1/2$ Mott insulating state. In this material, the approximate energy scale of a variety of interactions, involving spin-orbit coupling, magnetic exchange interaction, and the Mott gap, allows close coupling among the corresponding physical excitations, opening the possibility of cross control of the physical properties. Here, we experimentally demonstrate the effective gate control of both the transport and magnetism in a $\mathrm{S}{\mathrm{r}}_2\mathrm{Ir}{\mathrm{O}}_4$-based field effect transistor using an ionic liquid dielectric. This approach could go beyond the surface-limited field effect seen in conventional transistors, reflecting the unique aspect of the $J_{\mathrm{eff}}=1/2$ state. The simultaneous modulation of conduction and magnetism confirms the proposed intimate coupling of charge, orbital, and spin degrees of freedom in this oxide. These phenomena are probably related to an enhanced deviation from the ideal $J_{\mathrm{eff}}=1/2$ state due to the gate-promoted conduction. The present work would have important implications in modelling the unusual physics enabled by strong spin-orbit coupling and provides a new route to explore those emergent quantum phases in iridates.

It is shown that nanoparticles made of very low-$T_c$ superconductors have a large diamagnetic response at temperatures several orders of magnitude above $T_c$. Most of the features of the recently observed giant diamagnetism of Au nanorods are explained in terms of superconducting fluctuations, except for the huge magnitude of the effect.

We numerically calculated the localization length index $\nu$ and up to two subleading finite-size indices in the Chalker-Coddington network model of the plateau-plateau transitions in the quantum Hall effect. We also carried out fits with logarithmic corrections. The confidence intervals of the four fits for the exponent $\nu$ are narrow and overlap. The fit based on one relevant field and one marginal field is slightly more advantageous in comparison to the fits based on a relevant field and irrelevant field. The calculations were carried out by two different programs that produced close results, each one within the error bars of the other.

We investigate the ground- and excited-state properties of a two-dimensional charge-ordering system, and theoretically demonstrate that multielectron excitations by one photon occur substantially as a result of frustration effects. These multielectron excitations are naturally regarded as domain excitations, which involve a simultaneous excitation of a part of the system lattice. Furthermore, we show that such domain excitations not only suppress the original charge-ordering phase strongly but also enhance another phase of charge ordering. As a result of such a global change, the overall photoinduced optical conductivity spectra are also modified drastically from the original spectrum, with the modified spectra exhibiting midgap and gapless features.

It was recently pointed out that Halperin's 113 topological order explains the transport experiments in the quantum Hall liquid at filling factor $\nu =5/2$. The 113 order, however, cannot be easily distinguished from other likely topological orders at $\nu =5/2$ such as the non-Abelian Pfaffian and anti-Pfaffian states and the Abelian Halperin 331 state in Fabry-Pérot interferometry. We show that an electronic Mach-Zehnder interferometer provides a clear identification of these candidate $\nu =5/2$ states. Specifically, the $I\text{−}V$ curve for the tunneling current through the interferometer is more asymmetric in the 113 state than in other $\nu =5/2$ states. Moreover, the Fano factor for the shot noise in the interferometer can reach 13.6 in the 113 state, much greater than the maximum Fano factors of 3.2 in the Pfaffian and anti-Pfaffian states and 2.3 in the 331 state.

We report longitudinal ultrasound velocity measurements for magnetic fields up to 33 T applied parallel to the $a$ axis of the heavy electron compound ${\mathrm{UPt}}_3$. A characteristic dip in the sound velocity at the metamagnetic critical field $H_c=20\mathrm{T}$, reported in earlier work, is reproduced and shown to be independent of temperature at very low temperatures. We show that the single energy scale model [Shivaram et al., Phys. Rev. B 89, 241107(R) (2014)] captures the observed key features of the field dependence in the sound velocity shift $\delta v_s$. The shift $\delta v_s$ at $H_c$ is found to be inversely dependent on temperature above ∼3 K and assumes a fixed value at low $T$. This “saturation” in $\delta v_s$ below ∼3 K is accounted for by level broadening of the uranium spin states.

The thermal conductivity of a series of structural, diameter, and core/shell modulated silicon nanowires is computed by molecular dynamics simulations using the nonequilibrium method. The purpose of this study is to appraise the impact of surface roughness, amorphous parts integration, and diameter modulation on the thermal conductivity reduction. The addition of both amorphous regions and nanoconstrictions allows us to reach a thermal conductivity close to that of the amorphous pristine nanowires, while preserving a certain degree of crystallinity. This could result in interesting properties for thermoelectric applications.

The discovery of stable two-dimensional, earth-abundant, semiconducting materials is of great interest and may impact future electronic technologies. By combining global structural prediction and first-principles calculations, we have theoretically discovered several semiconducting silicon phosphide $({\mathrm{Si}}_x{\mathrm{P}}_y)$ monolayers, which could be formed stably at the stoichiometries of $y/x\ge 1$. Interestingly, some of these compounds, i.e., $P\text{−}6m2{\mathrm{Si}}_1{\mathrm{P}}_1$ and $Pm{\mathrm{Si}}_1{\mathrm{P}}_2$, have comparable or even lower formation enthalpies than their known allotropes. The band gaps $\left(E_g\right)$ of ${\mathrm{Si}}_x{\mathrm{P}}_y$ compounds can be dramatically tuned in an extremely wide range ($0<E_g<3$ eV) by simply changing the number of layers. Moreover, we find that carrier doping can drive the ground state of $C2/m{\mathrm{Si}}_1{\mathrm{P}}_3$ from a nonmagnetic state into a robust half-metallic spin-polarized state, originating from its unique valence band structure, which can extend the use of Si-related compounds for spintronics.

We theoretically predict instability of a zero-dc-current state of the two-dimensional electron system formed on the surface of liquid helium induced by the cyclotron resonance (CR). This conclusion follows from the theoretical analysis of the dc magnetoconductivity which takes into account the contribution from radiation in an exact way. A many-electron model of the dynamic structure factor of the 2D Coulomb liquid is used to describe the influence of strong internal forces acting between electrons. For low electron densities and high amplitudes of the microwave field, the dc magnetoconductivity is shown to become negative in the vicinity of the CR which causes the instability. This effect is strongly suppressed by Coulomb forces in the region of high densities.

We have performed a numerical study of the process of electron localization in reduced ceria. Our results show that different localized charge distributions can be attained in a bulk system by varying the lattice parameter. We demonstrate that the effect of electron localization is mainly determined by lattice relaxation and an accurate account for the effects of electronic correlation is necessary to achieve localized charge distribution.