Abstract: We report on the dynamical properties of interacting colloids confined to one dimension and subjected to external periodic energy landscapes. We particularly focus on the influence of hydrodynamic interactions on the mean-square displacement. Using Brownian dynamics simulations, we study colloidal systems with two types of repulsive interparticle interactions, namely, Yukawa and superparamagnetic potentials. We find that in the homogeneous case, hydrodynamic interactions lead to an enhancement of the particle mobility and the mean-square displacement at long times scales as t(alpha), with alpha = 1/2 + epsilon and epsilon being a small correction. This correction, however, becomes much more important in the presence of an external field, which breaks the homogeneity of the particle distribution along the line and, therefore, promotes a richer dynamical scenario due to the hydrodynamical coupling among particles. We provide here the complete dynamical scenario in terms of the external potential parameters: amplitude and commensurability.

Abstract: Using an effective one-dimensional cluster expansion in combination with first-principles electronic structure calculations we have studied the energetics and electronic properties of Sb-Te layered systems. For a Te concentration between 0 and 60 at. % an almost continuous series of metastable structures is obtained consisting of consecutive Sb bilayers next to consecutive Sb2Te3 units, with the general formula (Sb-2)(n)(Sb2Te3)(m) (n, m = 1,2, ... ). Between 60 and 100 at.% no stable structures are found. We account explicitly for the weak van derWaals bonding between Sb bilayers and Sb2Te3 units by using a recently developed functional, which strongly improves the interlayer bonding distances. At T = 0 K, no evidence is found for the existence of two separate single-phase regions delta and gamma and a two-phase region delta + gamma. Metastable compounds with a Te concentration between 0 and 40 at. % are semimetallic, whereas compounds with a Te concentration between 50 and 60 at. % are semiconducting. Compounds with an odd number of Sb layers are metallic and have a much higher formation energy than those with an even number of consecutive Sb layers, thereby favoring the formation of Sb bilayers.

Abstract: Quantum confinement of the transverse electron motion is the major effect governing the superconducting properties of high-quality metallic nanofilms, leading to a nonuniform transverse distribution of the superconducting condensate. In this case the order parameter can exhibit significant local enhancements due to these quantum-size effects and, consequently, quasiparticles have lower energies when they avoid the local enhancements of the pair condensate. Such excitations can be considered as new Andreev-type quasiparticles but now induced by quantum confinement. By numerically solving the Bogoliubovde Gennes equations and using Anderson's approximate solution to these equations, we: (a) formulate a criterion for such new Andreev-type states (NATS) and (b) study their effect on the superconducting characteristics in metallic nanofilms. We also argue that nanofilms made of low-carrier-density materials, e.g., of superconducting semiconductors, can be a more optimal choice for the observations of NATS and other quantum-size superconducting effects.

Abstract: We have grown epitaxial Cr-doped V2O3 thin films with Cr concentrations between 0% and 20% on (0001)-Al2O3 by oxygen-assisted molecular beam epitaxy. For the highly doped samples (>3%), a regular and monotonous increase of the resistance with decreasing temperature is measured. Strikingly, in the low doping samples (between 1% and 3%), a collapse of the insulating state is observed with a reduction of the low temperature resistivity by up to 5 orders of magnitude. A vacuum annealing at high temperature of the films recovers the low temperature insulating state for doping levels below 3% and increases the room temperature resistivity towards the values of Cr-doped V2O3 single crystals. It is well-know that oxygen excess stabilizes a metallic state in V2O3 single crystals. Hence, we propose that Cr doping promotes oxygen excess in our films during deposition, leading to the collapse of the low temperature insulating state at low Cr concentrations. These results suggest that slightly Cr-doped V2O3 films can be interesting candidates for field effect devices. (C) 2015 AIP Publishing LLC.

Abstract: We report on the observation of complex superlattices at the surface of the topological insulator Bi2Te3. Scanning tunneling microscopy reveals the existence of two different periodic structures in addition to the Bi2Te3 atomic lattice, which is found to strongly affect the local electronic structure. These three different periodicities are interpreted to result from a single small in-plane rotation of the topmost quintuple layer only. Density functional theory calculations support the observed increase in the DOS near the Fermi level, and exclude the possibility that strain is at the origin of the observed Moire pattern. Exploration of Moire superlattices formed by the quintuple layers of topological insulators holds great potential for further tuning of the properties of topological insulators.

Abstract: Using the tight-binding model, we investigate the influence of vacancy disorder on electrical transport in graphene Hall bars in the presence of quantizing magnetic fields. Disorder, induced by a random distribution of monovacancies, breaks the graphene sublattice symmetry and creates states localized on the vacancies. These states are observable in the bend resistance, as well as in the total DOS. Their energy is proportional to the square root of the magnetic field, while their localization length is proportional to the cyclotron radius. At the energies of these localized states, the electron current flows around the monovacancies and, as we show, it can follow unexpected paths depending on the particular arrangement of vacancies. We study how these localized states change with the vacancy concentration, and what are the effects of including the next-nearest-neighbor hopping term. Our results are also compared with the situation when double vacancies are present in the system. Double vacancies also induce localized states, but their energy and magnetic field dependencies are different. Their localization energy scales linearly with the magnetic field, and their localization length appears not to depend on the field strength.

Abstract: We calculate the spin-polarized electronic transport through a molecular bilayer spin valve from first principles, and establish the link between the magnetoresistance and the spin-dependent interactions at the metal-molecule interfaces. The magnetoresistance of a Fe vertical bar bilayer-C-70 vertical bar Fe spin valve attains a high value of 70% in the linearresponse regime, but it drops sharply as a function of the applied bias. The current polarization has a value of 80% in linear response and also decreases as a function of bias. Both these trends can be modeled in terms of prominent spin-dependent Fe vertical bar C-70 interface states close to the Fermi level, unfolding the potential of spinterface science to control and optimize spin currents.

Abstract: Recent experimental work on the application of graphene for novel illumination motivated us to present a theoretical study of the blackbody radiation emission from a freely suspended graphene driven by a dc electric field. Strong terahertz (THz) emission, with intensity up to mW/cm(2), can be generated with increasing electric field strength due to the heating of electrons in graphene. We show that the intensity of the THz emission generated electrically from graphene depends rather sensitively on the lattice temperature in relatively weak electric fields, whereas it is less sensitive to the lattice temperature in relative strong electric fields. Our study highlights the practical application of graphene as intense THz source where the radiation is generated electrically. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract: We present the Tight-Binding Studio (TB Studio) software package that calculates the different parameters of a tight-binding Hamiltonian from a set of Bloch energy bands obtained from first principle theories such as density functional theory, Hartree-Fock calculations or semi-empirical band-structure theory. This will be helpful for scientists who are interested in studying electronic and optical properties of structures using Green's function theory within the tight-binding approximation. TB Studio is a cross-platform application written in C++ with a graphical user interface design that is user-friendly and easy to work with. This software is powered by Linear Algebra Package C interface library for solving the eigenvalue problems and the standard high performance OpenGL graphic library for real time plotting. TB Studio and its examples together with the tutorials are available for download from tight-binding.com. Program summary Program Title: Tight-Binding Studio Program Files doi:http://dx.doi.org/10.17632/j6x5mwzm2d.1 Licensing provisions: LGPL Programming language: C++ External routines: BLAS, LAPACK, LAPACKE, wxWidgets, OpenGL, MathGL Nature of problem: Obtaining Tight-Binding Hamiltonian from a set of Bloch energy bands obtained from first-principles calculations. Solution method: Starting from the simplified LCAO method, a tight-binding model in the two-center approximation is constructed. The Slater and Koster (SK) approach is used to calculate the parameters of the TB Hamiltonian. By using non-linear fitting approaches the optimal values of the SK parameters are obtained such that the TB energy eigenvalues are as close as possible to those from first-principles calculations. We obtain the expression for the Hamiltonian and the overlap matrix elements between the different orbitals of the different atoms in an orthogonal or non-orthogonal basis set. (C) 2020 Elsevier B.V. All rights reserved.

Abstract: Ultrafine ZnO nanocrystals with a thickness down to 0.25 nm are grown by a metalorganic chemical vapor deposition method. Electronic band structures and native point defects of ZnO nanocrystals are studied by a combination of scanning tunneling microscopy/spectroscopy and first-principles density functional theory calculations. Below a critical thickness of nm ZnO adopts a graphitic-like structure and exhibits a wide band gap similar to its wurtzite counterpart. The hexagonal wurtzite structure, with a well-developed band gap evident from scanning tunneling spectroscopy, is established for a thickness starting from similar to 1.4 nm. With further increase of the thickness to 2 nm, V-O-V-Zn defect pairs are easily produced in ZnO nanocrystals due to the self-compensation effect in highly doped semiconductors.