2,658 research outputs found
Band-Structure Effects in the Spin Relaxation of Conduction Electrons
Spin relaxation of conduction electrons in metals is significantly influenced
by the Fermi surface topology. Electrons near Brillouin zone boundaries,
special symmetry points, or accidental degeneracy lines have spin flip rates
much higher than an average electron. A realistic calculation and analytical
estimates show that these regions dominate the spin relaxation, explaining why
polyvalent metals have much higher spin relaxation rates (up to three orders of
magnitude) than similar monovalent metals. This suggests that spin relaxation
in metals can be tailored by band-structure modifications like doping,
alloying, reducing the dimensionality, etc.Comment: 10 pages, 2 figures; to appear in the 43rd MMM Conference Proceedings
published in the JA
Energy relaxation of an excited electron gas in quantum wires: many-body electron LO-phonon coupling
We theoretically study energy relaxation via LO-phonon emission in an excited
one-dimensional electron gas confined in a GaAs quantum wire structure. We find
that the inclusion of phonon renormalization effects in the theory extends the
LO-phonon dominated loss regime down to substantially lower temperatures. We
show that a simple plasmon-pole approximation works well for this problem, and
discuss implications of our results for low temperature electron heating
experiments in quantum wires.Comment: 10 pages, RevTex, 4 figures included. Also available at
http://www-cmg.physics.umd.edu/~lzheng
Dynamic Scaling in a 2+1 Dimensional Limited Mobility Model of Epitaxial Growth
We study statistical scale invariance and dynamic scaling in a simple
solid-on-solid 2+1 - dimensional limited mobility discrete model of
nonequilibrium surface growth, which we believe should describe the low
temperature kinetic roughening properties of molecular beam epitaxy. The model
exhibits long-lived ``transient'' anomalous and multiaffine dynamic scaling
properties similar to that found in the corresponding 1+1 - dimensional
problem. Using large-scale simulations we obtain the relevant scaling
exponents, and compare with continuum theories.Comment: 5 pages, 4 ps figures included, RevTe
Magnetic Percolation and the Phase Diagram of the Disordered RKKY model
We consider ferromagnetism in spatially randomly located magnetic moments, as
in a diluted magnetic semiconductor, coupled via the carrier-mediated indirect
exchange RKKY interaction. We obtain via Monte Carlo the magnetic phase diagram
as a function of the impurity moment density and the relative carrier
concentration . As evidenced by the diverging correlation length
and magnetic susceptibility, the boundary between ferromagnetic (FM) and
non-ferromagnetic (NF) phases constitutes a line of zero temperature critical
points which can be viewed as a magnetic percolation transition. In the dilute
limit, we find that bulk ferromagnetism vanishes for . We also
incorporate the local antiferromagnetic direct superexchange interaction
between nearest neighbor impurities, and examine the impact of a damping factor
in the RKKY range function.Comment: 5 pages, 3 figures; figure formatting modified, typos fixe
Critical behavior of diluted magnetic semiconductors: the apparent violation and the eventual restoration of the Harris criterion for all regimes of disorder
Using large-scale Monte Carlo calculations, we consider strongly disordered
Heisenberg models on a cubic lattice with missing sites (as in diluted magnetic
semiconductors such as Ga_{1-x}Mn_{x}As). For disorder ranging from weak to
strong levels of dilution, we identify Curie temperatures and calculate the
critical exponents nu, gamma, eta, and beta finding, per the Harris criterion,
good agreement with critical indices for the pure Heisenberg model where there
is no disorder component. Moreover, we find that thermodynamic quantities (e.g.
the second moment of the magnetization per spin) self average at the
ferromagnetic transition temperature with relative fluctuations tending to zero
with increasing system size. We directly calculate effective critical exponents
for T > T_{c}, yielding values which may differ significantly from the critical
indices for the pure system, especially in the presence of strong disorder.
Ultimately, the difference is only apparent, and eventually disappears when T
is very close to T_{c}.Comment: 11 pages, 9 figure
Valley interference effects on a donor electron close to a Si/SiO2 interface
We analyze the effects of valley interference on the quantum control and
manipulation of an electron bound to a donor close to a Si/SiO2 interface as a
function of the valley-orbit coupling at the interface. We find that, for
finite valley-orbit coupling, the tunneling times involved in shuttling the
electron between the donor and the interface oscillate with the interface/donor
distance in much the same way as the exchange coupling oscillates with the
interdonor distance. These oscillations disappear when the ground state at the
interface is degenerate (corresponding to zero valley-orbit coupling).Comment: 7 pages, 5 figure
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