Charged basal stacking fault (BSF) scattering in nitride semiconductors

A theory of charge transport in semiconductors in the presence of basal stacking faults is developed. It is shown that the presence of basal stacking faults leads to anisotropy in carrier transport. The theory is applied to carrier transport in non-polar GaN films consisting of a large number BSFs, and the result is compared with experimental data.Comment: 4 pages, 3 figure

Multiband effective bond-orbital model for nitride semiconductors with wurtzite structure

A multiband empirical tight-binding model for group-III-nitride semiconductors with a wurtzite structure has been developed and applied to both bulk systems and embedded quantum dots. As a minimal basis set we assume one s-orbital and three p-orbitals, localized in the unit cell of the hexagonal Bravais lattice, from which one conduction band and three valence bands are formed. Non-vanishing matrix elements up to second nearest neighbors are taken into account. These matrix elements are determined so that the resulting tight-binding band structure reproduces the known Gamma-point parameters, which are also used in recent kp-treatments. Furthermore, the tight-binding band structure can also be fitted to the band energies at other special symmetry points of the Brillouin zone boundary, known from experiment or from first-principle calculations. In this paper, we describe details of the parametrization and present the resulting tight-binding band structures of bulk GaN, AlN, and InN with a wurtzite structure. As a first application to nanostructures, we present results for the single-particle electronic properties of lens-shaped InN quantum dots embedded in a GaN matrix.Comment: 10 pages, 5 figures, two supplementary file

Simulating sympathetic cooling of atomic mixtures in nonlinear traps

We discuss the dynamics of sympathetic cooling of atomic mixtures in realistic, nonlinear trapping potentials using a microscopic effective model developed earlier for harmonic traps. We contrast the effectiveness of different atomic traps, such as Ioffe-Pritchard magnetic traps and optical dipole traps, and the role their intrinsic nonlinearity plays in speeding up or slowing down thermalization between the two atomic species. This discussion includes cases of configurations with lower effective dimensionality. From a more theoretical standpoint, our results provide the first exploration of a generalized Caldeira-Leggett model with nonlinearities both in the trapping potential as well as in the interspecies interactions, and no limitations on their coupling strength.Comment: 11 pages, 7 figure

Single-spin-flip dynamics of the Ising chain

We consider the most general single-spin-flip dynamics for the ferromagnetic Ising chain with nearest-neighbour influence and spin reversal symmetry. This dynamics is a two-parameter extension of Glauber dynamics corresponding respectively to non-linearity and irreversibility. The associated stationary state measure is given by the usual Boltzmann-Gibbs distribution for the ferromagnetic Hamiltonian of the chain. We study the properties of this dynamics both at infinite and at finite temperature, all over its parameter space, with particular emphasis on special lines and points.Comment: 31 pages, 18 figure

Thermodynamics of Large-N_f QCD at Finite Chemical Potential

We extend the previously obtained results for the thermodynamic potential of hot QCD in the limit of large number of fermions to non-vanishing chemical potential. We give exact results for the thermal pressure in the entire range of temperature and chemical potential for which the presence of a Landau pole is negligible numerically. In addition we compute linear and non-linear quark susceptibilities at zero chemical potential, and the entropy at small temperatures. We compare with the available perturbative results and determine their range of applicability. Our numerical accuracy is sufficiently high to check and verify existing results, including the recent perturbative results by Vuorinen on quark number susceptibilities and the older results by Freedman and McLerran on the pressure at zero temperature and high chemical potential. We also obtain a number of perturbative coefficients at sixth order in the coupling that have not yet been calculated analytically. In the case of both non-zero temperature and non-zero chemical potential, we investigate the range of validity of a scaling behaviour noticed recently in lattice calculations by Fodor, Katz, and Szabo at moderately large chemical potential and find that it breaks down rather abruptly at $\mu_q \gtrsim \pi T$, which points to a presumably generic obstruction for extrapolating data from small to large chemical potential. At sufficiently small temperatures $T \ll \mu_q$, we find dominating non-Fermi-liquid contributions to the interaction part of the entropy, which exhibits strong nonlinearity in the temperature and an excess over the free-theory value.Comment: 18 pages, 7 figures, JHEP style; v2: several updates, rewritten and extended sect. 3.4 covering now "Entropy at small temperatures and non-Fermi-liquid behaviour"; v3: additional remarks at the end of sect. 3.4; v4: minor corrections and additions (version to appear in JHEP