J. Mašek

Local environment effects in electronic structure: a-GeS contrasted to a-SiHx

Abstract We used Bethe lattice approach and large-scale modelling followed by recursion method calculation to describe the electronic structures of a-GeS and a-SiH x , which have different nature resulting from different topology and different concentration of heteropolar bonds.

Frequency Dependent Transport in Quantum Coherent Systems

At low enough temperatures the electrical transport properties of small conductors exhibit a rich variety of quantum phenomena due to the suppression of inelastic, phase randomizing scattering. They are related to finite size quantization, and to the coherence of the electron states throughout the whole sample. For the theoretical description of these mesoscopic effects one needs 1. information about the single particle quantum states in finite, but not atomic(!), systems in the presence of disorder, 2. a suitable transport theory that includes the effect of contacts and leads, and 3. information about the influence of interactions on the states, and on the transport processes.

Frequency-Dependent Transport in Quantum Wires

Coherent quantum transport phenomena have been the subject of many theoretical and experimental studies since the discovery of quantum interference oscillations in the magnetoresistance of thin metallic cylinders (Altshuler et al., 1981; Sharvin and Sharvin, 1981). Universal reproducible stochastic fluctuations in the magnetoresistance of small metallic systems (Washburn and Webb, 1986) have been attributed to the interference of elastically scattered electrons at randomly distributed impurities. In quasi one-dimensional inversion layers in Mosfets, similar fluctuations have been observed when changing the gate voltage at low temperatures (Fowler et al., 1982). They are due to localisation of electron states. Most recently, a new quantisation phenomenon was discovered in the conductance of geometrically constricted inversion layers of high-quality GaA1As heterostructures (van Wees et al, 1988; Wharam et al., 1988). It is believed that in these systems, at very low temperatures (< 1K) the electrons behave coherently and are not scattered elastically within distances of several p.m, due to the absence of phase-randomising scattering events and of impurities. The quantisation of the conductance can then be interpreted as a consequence of the size quantisation of the electronic energy levels (Imry, 1986; Sharvin, 1965; Johnston and Schweitzer, 1988; Kramer and Masek, 1988; Isawa, 1988; Kawabata, 1989).

The electronic structure of a-SiHx alloys

We use a tight binding method to model the electronic structure of a-SiH x for various regimes of hydrogen bonding and calculate the local densities of states for random alloys consisting of Si and SiH 2 units and for a line defect decorated by hydrogen atoms.

The localisation length and the density of states in correlated random systems

Abstract The theory of Markov processes is applied to the problem of modelling correlated random potentials. The consequences of introducing correlations for the localisation length and the density of states are investigated.