2,543 research outputs found
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 , which points to a
presumably generic obstruction for extrapolating data from small to large
chemical potential. At sufficiently small temperatures , 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
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