Coarsened Lattice Spatial Disorder in the Thermodynamic Limit

In this Rapid Research Note the application of recently introduced [Physica A 277 (2000) 157] entropic measure S_Delta of spatial disorder for systems of finite-sized objects is presented. In the thermodynamic limit the critical behaviour of coarsened lattice model of random two-phase systems is illustrated for certain grain size distributions (GSDs) and chosen parameters. Also the changes of spatial disorder, quantified by S_Delta, between the limit GSDs clearly show that the topological equivalence of the two phases is broken.Comment: 3 pages, 1 figur

Coulomb gap in a model with finite charge transfer energy

The Coulomb gap in a donor-acceptor model with finite charge transfer energy $\Delta$ describing the electronic system on the dielectric side of the metal-insulator transition is investigated by means of computer simulations on two- and three-dimensional finite samples with a random distribution of equal amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry of the model presented with respect to the exchange of donors and acceptors are derived. In the immediate neighborhood of the Fermi energy $\mu$ the the density of one-electron excitations $g(\epsilon)$ is determined solely by finite size effects and $g(\epsilon)$ further away from $\mu$ is described by an asymmetric power law with a non-universal exponent, depending on the parameter $\Delta$.Comment: 10 pages, 6 figures, submitted to Phys. Rev.

Non-ergodic effects in the Coulomb glass: specific heat

We present a numerical method for the investigation of non-ergodic effects in the Coulomb glass. For that, an almost complete set of low-energy many-particle states is obtained by a new algorithm. The dynamics of the sample is mapped to the graph formed by the relevant transitions between these states, that means by transitions with rates larger than the inverse of the duration of the measurement. The formation of isolated clusters in the graph indicates non-ergodicity. We analyze the connectivity of this graph in dependence on temperature, duration of measurement, degree of disorder, and dimensionality, studying how non-ergodicity is reflected in the specific heat.Comment: Submited Phys. Rev.

Universal Crossover between Efros-Shklovskii and Mott Variable-Range-Hopping Regimes

A universal scaling function, describing the crossover between the Mott and the Efros-Shklovskii hopping regimes, is derived, using the percolation picture of transport in strongly localized systems. This function is agrees very well with experimental data. Quantitative comparison with experiment allows for the possible determination of the role played by polarons in the transport.Comment: 7 pages + 1 figure, Revte

Structure and quasiparticle energies of cubic, wurtzite and hexagonal Boron Nitride

We present local density functional theory (DFT-LDA) studies of the structural properties of boron nitride in the layered hexagonal (h-BN), zincblende (c-BN), and wurtzite (w-BN) structures, performed using a fast implementation of the norm-conserving pseud-opotential plane-wave method. Quasiparticle band structures are then calculated for all phases by means of an efficient GW self-energy scheme. To our knowledge, these are the first GW quasiparticle calculations for wurtzite BN including local-field and dynamical screening effects. DFT-LDA band gaps as functions of pressure and uniaxial distorsion for h-BN are also discussed