We present a tunnel spectroscopy study of the electronic spectrum of single magnetite ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles trapped between nanometer-spaced electrodes. The Verwey transition is clearly identified in the current-voltage characteristics where we find that the transition temperature is electric field dependent. The data show the presence of localized states at high energy, $\varepsilon \sim 0.6$ eV, which can be attributed to polaron states. At low energy, the density of states (DOS) is suppressed at the approach of the Verwey transition. Below the Verwey transition, a gap, $\Delta \sim 300$ meV, is observed in the spectrum. In contrast, no gap is observed in the high temperature phase, implying that electronic transport in this phase is possibly due to polaron hopping with activated mobility.

Recently, it was reported that the skutterudite-related ${\mathrm{Ce}}_3{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ heavy fermion compound has a large electronic specific heat coefficient $C\left(T\right)/T$ and short-range magnetic correlations, both suggest a possible quantum critical point (QCP). We present the low-temperature specific heat, resistivity, and susceptibility of ${\mathrm{Ce}}_{1\text{−}x}{\mathrm{La}}_x{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$, which do not confirm the presence of QCP. X-ray photoelectron spectroscopy revealed a stable configuration of Ce atoms consistent with magnetic susceptibility data. Magnetic susceptibility shows that the sixfold-degenerate multiplet of ${\mathrm{Ce}}^{3+}$ ion splits into three doublets due to the lower local symmetry of ${\mathrm{CeSn}}_{12}$ cage in the cubic ${\mathrm{Ce}}_{1\text{−}x}{\mathrm{La}}_x{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ compounds. The resistivity, specific heat, and susceptibility data are consistent with our band-structure calculations. The chemical bondings in the unit cell of ${\mathrm{Ce}}_{1\text{−}x}{\mathrm{La}}_x{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$, analyzed based on the difference charge density maps from band-structure calculations within the virtual crystal approximation explain the deformation of the cages and the crystal electric field properties of the system.

In a recent work [Merker, Kirchner, Muñoz, and Costi, Phys. Rev. B 87, 165132 (2013)], the authors compared the results of numerical renormalization group (NRG) and a perturbative approach for the dependence on temperature $T$ and magnetic field $B$ of the conductance through a quantum dot described by the impurity Anderson model, for small $T$ and $B$. We show that the equation used to extract the dependence on $B$ from NRG results is incorrect out of the particle-hole symmetric case. As a consequence, in the Kondo regime, the correct NRG results have a weaker dependence on $B$ and the disagreement between both approaches increases.

The Comment of A. A. Aligia claims that the superperturbation theory (SPT) approach [E. Muñoz, C. J. Bolech, and S. Kirchner, Phys. Rev. Lett. 110, 016601 (2013)] formulated using dual fermions [A. N. Rubtsov, M. I. Katsnelson, and A. I. Lichtenstein, Phys. Rev. B 77, 033101 (2008)] and used by us to compare with numerical renormalization group (NRG) results for the conductance [L. Merker, S. Kirchner, E. Muñoz, and T. A. Costi, Phys. Rev. B 87, 165132 (2013)], fails to correctly extend the results of the symmetric Anderson impurity model (SIAM) for general values of the local level $E_d$ in the Kondo regime. We answer this criticism. We also compare new NRG results for $c_B$, with $c_B$ calculated directly from the low-field conductance, with new higher-order SPT calculations for this quantity, finding excellent agreement for all $E_d$ and for $U/\pi \Delta$ extending into the strong coupling regime.

Time- and angle-resolved two-photon photoemission (2PPE) was used to study the electronic structure and ultrafast electron dynamics of the $p$-doped topological insulator ${\mathrm{Sb}}_2{\mathrm{Te}}_3$ and its derivative ${\mathrm{Sb}}_2{\mathrm{Te}}_2\mathrm{S}$. Our 2PPE experiments directly reveal that the massless Dirac-cone like energy dispersion of topological surface states is realized above the Fermi energy in both materials. The observed bulk conduction bands of ${\mathrm{Sb}}_2{\mathrm{Te}}_2\mathrm{S}$ are found to be shifted to higher energies as compared to ${\mathrm{Sb}}_2{\mathrm{Te}}_3$. This shift has, however, surprisingly almost no influence on the electron dynamics in the topological surface state, which proceed on a picosecond time scale.

We present a study of $\delta$ doping at the ${\mathrm{LaTiO}}_3/{\mathrm{SrTiO}}_3$ interface with isostructural antiferromagnetic perovskite ${\mathrm{LaCrO}}_3$ that dramatically alters the properties of the two-dimensional electron gas at the interface. The effects include a reduction in sheet-carrier density, prominence of the low-temperature resistivity minimum, enhancement of weak antilocalization below 10 K, and observation of a strong anisotropic magnetoresistance (MR). The positive and negative MR for out-of-plane and in-plane fields, respectively, and the field and temperature dependencies of MR suggest Kondo scattering by localized ${\mathrm{Ti}}^{3+}$ moments renormalized by spin-orbit interaction at T $<$ 10 K, with the increased $\delta$-layer thickness. Electron-energy-loss spectroscopy and density functional calculations provide convincing evidence of blocking of electron transfer from LTO to STO by the $\delta$ layer.

Currently, there is much interest in discovering analytically tractable $\left(3+1\right)$-dimensional models that describe interacting fermions with emerging topological properties. Towards that end we present a three-dimensional tight-binding model of spinless interacting fermions that reproduces, in the low-energy limit, a $\left(3+1\right)$-dimensional Abelian topological quantum field theory called the BF model. By employing a mechanism equivalent to Haldane's Chern insulator, we can turn the noninteracting model into a three-dimensional chiral topological insulator. We then isolate energetically one of the two Fermi points of the lattice model. In the presence of suitable fermionic interactions, the system, in the continuum limit, is equivalent to a generalized $\left(3+1\right)$-dimensional Thirring model. The low-energy limit of this model is faithfully described by the BF theory. Our approach directly establishes the presence of $\left(2+1\right)$-dimensional BF theory at the boundary of the lattice and it provides a way to detect the topological order of the model through fermionic density measurements.

Topological insulators are of interest for many applications in electronics and optoelectronics, but harnessing their unique properties requires detailed understanding and control of charge injection at electrical contacts. Here we present large-scale ab initio calculations of the electronic properties of Au, Ni, Pt, Pd, and graphene contacts to ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. We show that regardless of the metal, the Fermi level is located in the conduction band, leading to $n$-type Ohmic contact to the first quintuplet. Furthermore, we find strong charge transfer and band bending in the first few quintuplets, with no Schottky barrier for charge injection even when the topological insulator is undoped. Our calculations indicate that Au and graphene leave the spin-momentum locking mostly unaltered, but on the other hand, Ni, Pd, and Pt strongly hybridize with ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and relax spin-momentum locking. Our results indicate that judicious choice of the contact metal is essential to reveal the unique surface features of topological insulators.

Interaction between the lattice and the orbital degrees of freedom not only makes rare-earth nickelates unusually “bad metal,” but also introduces a temperature-driven insulator-metal phase transition. Here we investigate this insulator-metal phase transition in thin films of ${\mathrm{SmNiO}}_3$ using the slow time-dependent fluctuations (noise) in resistivity. The normalized magnitude of noise is found to be extremely large, being nearly eight orders of magnitude higher than thin films of common disordered metallic systems, and indicates electrical conduction via classical percolation in a spatially inhomogeneous medium. The higher-order statistics of the fluctuations indicate a strong non-Gaussian component of noise close to the transition, attributing the inhomogeneity to the coexistence of the metallic and insulating phases. Our experiment offers insight into the impact of lattice-orbital coupling on the microscopic mechanism of electron transport in the rare-earth nickelates.

We study the evolution of magnetic structures driven by a synthetic spin-orbit coupling in a one-dimensional two-component Bose-Hubbard model. In addition to the Mott insulator-superfluid transition, in the Mott insulator phases we found a transition from a gapped ferromagnetic phase to a gapless chiral phase by increasing the strength of the spin-orbit coupling. Further increasing the spin-orbit coupling drives a transition from the gapless chiral phase to a gapped antiferromagnetic phase. These magnetic structures persist in superfluid phases. In particular, in the chiral Mott insulator and chiral superfluid phases, incommensurability is observed in characteristic correlation functions. These unconventional Mott insulator phase and superfluid phase demonstrate the different effects arising from the competition between the kinetic energy and the spin-orbit coupling.

The formation of a Schottky barrier at the interface between a metal and hexagonal boron nitride $(h-\mathrm{BN})$ is studied using density functional theory. For metals whose work functions range from 4.2 to 6.0 eV, we find Schottky barrier heights for holes between 1.2 and 2.3 eV. A central role in determining the Schottky barrier height is played by a potential step of between 0.4 and 1.8 eV that is formed at the $\mathrm{metal}|h-\mathrm{BN}$ interface and effectively lowers the metal work function. If $h-\mathrm{BN}$ is physisorbed, as is the case on fcc Cu, Al, Au, Ag, and Pt(111) substrates, the interface potential step is described well by a universal function that depends only on the distance separating $h-\mathrm{BN}$ from the metal surface. The interface potential step is largest when $h-\mathrm{BN}$ is chemisorbed, which is the case for hcp Co and Ti (0001) and for fcc Ni and Pd (111) substrates.

We report on nonequilibrium transport features observed in experiments using three-dimensional amorphous indium-oxide films. It is demonstrated that all the features that characterize intrinsic electron glasses which heretofore were seen in two-dimensional samples are also observed in field-effect measurements of systems that exhibit three-dimensional variable range hopping. In particular, a memory dip is observed in samples configured with gate. The memory-dip width and magnitude support models that associate the phenomenon with the Coulomb gap. The memory dip and the glassy effects disappear once the quenched disorder in the system is reduced and the system becomes diffusive. This happens when the Ioffe-Regel dimensional parameter $k_{\text{F}}\ell$ exceeds $\approx 0.3$, which is the critical value for the metal-to-insulator transition in all versions of the amorphous indium oxides [Phys. Rev. B 86, 165101 (2012)]. This confirms that being in the Anderson localized phase is a prerequisite for observing the memory dip and the associated glassy effects. The results of the gating experiments suggest that the out-of-equilibrium effect caused by inserted charge extends over spatial scales considerably larger than the screening length.

We report systematic ${}^{17}\mathrm{O-NMR}$ measurements on the high-$T_c$ cuprate $({\mathrm{Ca}}_x{\mathrm{La}}_{1-x}\left)\right({\mathrm{Ba}}_{1.75-x}{\mathrm{La}}_{0.25+x}){\mathrm{Cu}}_3{\mathrm{O}}_y$, for four different families (different $x)$. Using Knight shift data, we show that the pseudogap opening temperature $T^{*}$ is much higher than $T_c$ near optimal doping, unlike structurally similar YBCO. In addition, at constant doping the pseudogap temperature does not vary with $x$, in contrast to $T_c$. This puts constraints on the nature of the pseudogap and position of the quantum critical point inside the superconducting dome.

Resonance Raman scattering (RRS) of two model perovskite-type $\left({\mathrm{ABO}}_3\right)$ relaxor compounds ${\mathrm{PbSc}}_{0.5}{\mathrm{Ta}}_{0.5}{\mathrm{O}}_3$ (PST) and ${\mathrm{PbSc}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_3$ (PSN) excited with a laser wavelength of 325 nm (3.8 eV) is studied at different temperatures and ambient pressure as well as at high pressures and room temperature (for PST). The origin of the observed RRS is reinspected by applying group-theory analysis of phonons compatible with symmetry-allowed electron transitions in cubic and possible polar and nonpolar rhombohedral ferroic structures. It is shown that the simultaneous enhancement of first- and second-order RRS generated by antisymmetric ${\mathrm{BO}}_6$ bending and stretching modes under resonance conditions when the photon energy is slightly above the energy gap $E_g\sim 3.2\text{eV}$ results exclusively from spatial regions with coherent polar structural distortions. Upon cooling RRS appears in the vicinity of the characteristic temperature $T^{*}$, and its total intensity significantly increases upon further temperature decrease. The predominate type of ${\mathrm{BO}}_6$ polarity changes from related to difference in B-O bonds to related to distorted O-B-O bond angles. At room temperature and high pressures RRS drops in intensity above the critical pressure of development of long-range antiphase octahedral tilting. However it persists up to 8.3 GPa, which is the highest pressure reached in the experiment, indicating that the high-pressure phase is polar due to the slight ${\mathrm{BO}}_6$ distortions accompanying the tilt order.

We report an experimental study of surface electrons on liquid helium-4 under cyclotron resonant excitation. Significant resonance-induced redistribution of electron density due to overheating was observed. Analysis of redistributed charges indicates an unusually large expansion of the electron system in a lateral direction, which cannot be understood in the framework of the generally accepted effective electron temperature approximation. To interpret the data we suggest that under resonant cyclotron pumping, a fraction of nonthermalized electrons is formed, in which the average energy associated with electron in-plane motion can significantly exceed the average energy associated with motion perpendicular to the helium surface.

A theory of polaritonic states is developed for a nanostructure with a wide quantum well stressed perpendicular to the growth axis of the heterostructure. The role of the $K$-linear terms appearing in the exciton Hamiltonian under the stress is discussed. Exciton reflectance spectra are theoretically modeled for the nanostructure. It is predicted that the spectral oscillations caused by interference of the excitonlike and photonlike polariton modes disappear with the increase of applied pressure and then appear again with the opposite phase relative to that observed at low pressure. Effects of gyrotropy and convergence of masses of excitons with heavy and light holes due to their mixing by the deformation are also considered. Numerical estimates performed for the GaAs wells show that these effects can be experimentally observed at pressure $P<1$ GPa for the well widths of a fraction of a micron.

The electronic states of a mesoscopic ring are assessed in the presence of Rashba spin-orbit (SO) coupling and a $\text{U}\left(1\right)$ gauge field. Spin-symmetric coupling to an ideal lead is implemented following Büttiker's voltage probe. The exact density of states is derived using the reservoir uncoupled eigenstates as basis functions mixed by the reservoir coupling. The decay time of uncoupled electron eigenstates is derived by fitting the broadening profiles. Spin and charge persistent currents are computed in the presence of the SO interaction and the reservoir coupling for two distinct scenarios of the electron filling fraction. The degradation of the persistent currents depends uniformly on the reservoir coupling but nonuniformly in temperature, the latter due to the fact that currents emerge from different depths of the Fermi sea, and thus for some regimes of flux, they are provided with a protective gap. Such flux regimes can be tailored by the SO coupling for both charge and spin currents.