Quantum Hall Resistance Overshoot in 2-Dimensional Electron Gases - Theory and Experiment

We present a systematical experimental investigation of an unusual transport phenomenon observed in two dimensional electron gases in Si/SiGe heterostructures under integer quantum Hall effect (IQHE) conditions. This phenomenon emerges under specific experimental conditions and in different material systems. It is commonly referred to as Hall resistance overshoot, however, lacks a consistent explanation so far. Based on our experimental findings we are able to develop a model that accounts for all of our observations in the framework of a screening theory for the IQHE. Within this model the origin of the overshoot is attributed to a transport regime where current is confined to co-existing evanescent incompressible strips of different filling factors.Comment: 26 pages, 10 figure

The visibility of IQHE at sharp edges: Experimental proposals based on interactions and edge electrostatics

The influence of the incompressible strips on the integer quantized Hall effect (IQHE) is investigated, considering a cleaved-edge overgrown (CEO) sample as an experimentally realizable sharp edge system. We propose a set of experiments to clarify the distinction between the large-sample limit when bulk disorder defines the IQHE plateau width and the small-sample limit smaller than the disorder correlation length, when self-consistent edge electrostatics define the IQHE plateau width. The large-sample or bulk QH regime is described by the usual localization picture, whereas the small-sample or edge regime is discussed within the compressible/incompressible strips picture, known as the screening theory of QH edges. Utilizing the unusually sharp edge profiles of the CEO samples, a Hall bar design is proposed to manipulate the edge potential profile from smooth to extremely sharp. By making use of a side-gate perpendicular to the two dimensional electron system, it is shown that the plateau widths can be changed or even eliminated altogether. Hence, the visibility of IQHE is strongly influenced when adjusting the edge potential profile and/or changing the dc current direction under high currents in the non-linear transport regime. As a second investigation, we consider two different types of ohmic contacts, namely highly transmitting (ideal) and highly reflecting (non-ideal) contacts. We show that if the injection contacts are non-ideal, however still ohmic, it is possible to measure directly the non-quantized transport taking place at the bulk of the CEO samples. The results of the experiments we propose will clarify the influence of the edge potential profile and the quality of the contacts, under quantized Hall conditions.Comment: Substantially revised version of manuscript arXiv:0906.3796v1, including new figures et

First Principles Study of Phonon Dispersion Curved for Yttrium Nitride

We present first-principles calculations of the structural and lattice-dynamical properties for cubic yttrium nitride. The ground state properties, such as the lattice constant and the bulk modulus, are calculated using a plane wave pseudopotential method within density functional theory. A linear-response approach to density functional theory is used to derive the phonon frequencies. In this work, we present plane-wave pseudopotential calculations within density functional theory and calculate the phonon frequencies for high symmetry points. DOI: 10.12693/APhysPolA.123.31

First-principles investigation of bowing parameter in zinc-blende ScxGa1-xN

We present first-principles calculations of the structural and electronic properties of binary GaN, ScN an

First-principles calculations of structural and electronic properties of TlxGa1-xAs alloys

The zincblende ternary alloys TlxGa1-xAs (0 < x < 1) are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation. To model the alloys, 16-atom supercells with the 2 x 2 x 2 dimensions are used and the dependency of the lattice parameter, bulk modulus, electronic structure, energy band gap, and optical bowing on the concentration x are analyzed. The results indicate that the ternary TlxGa1-xAs alloys have an average band gap bowing parameter of 4.48 eV for semiconductor alloys and 2.412 eV for semimetals. It is found that the band gap bowing strongly depends on composition and alloying a small Tl content with GaAs produces important modifications in the band structures of the alloys