11,932 research outputs found
Spin-orbit coupling induced by a mass gradient
The existence of a spin-orbit coupling (SOC) induced by the gradient of the
effective mass in low-dimensional heterostructures is revealed. In structurally
asymmetric quasi-two-dimensional semiconductor heterostructures the presence of
a mass gradient across the interfaces results in a SOC which competes with the
SOC created by the electric field in the valence band. However, in graded
quantum wells subjected to an external electric field, the mass-gradient
induced SOC can be finite even when the electric field in the valence band
vanishes.Comment: 4 pages, 2 figures, 1 tabl
Role of gauge invariance in B -> V gamma radiative weak decays
The role of gauge invariance in calculating B -> V gamma radiative weak
decays is clarified. It is shown that the gauge invariance severely restricts
the contributions mediated by the usual weak non-leptonic Hamiltonian dominated
by u and c quaks with one photon attachment. Such contributions are found to be
almost negligible.Comment: 5 pages, Revtex, no figure
Probing the largest scale structure in the universe with polarization map of galaxy clusters
We introduce a new formalism to describe the polarization signal of galaxy
clusters on the whole sky. We show that a sparsely sampled, half-sky map of the
cluster polarization signal at would allow to better characterize the
very large scale density fluctuations. While the horizon length is smaller in
the past, two other competing effects significantly remove the contribution of
the small scale fluctuations from the quadrupole polarization pattern at . For the standard Lambda-CDM universe with vanishing tensor mode, the
quadrupole moment of the temperature anisotropy probed by WMAP is expected to
have a ~32% contribution from fluctuations on scales below 6.3h^{-1}Gpc. This
percentage would be reduced to ~2% level for the quadrupole moment of
polarization pattern at . A cluster polarization map at
would shed light on the potentially anomalous features of the largest scale
structure in the observable universe.Comment: 5 pages, 2 figures, revised version, to appear in PR
Quantum corrected Langevin dynamics for adsorbates on metal surfaces interacting with hot electrons
We investigate the importance of including quantized initial conditions in
Langevin dynamics for adsorbates interacting with a thermal reservoir of
electrons. For quadratic potentials the time evolution is exactly described by
a classical Langevin equation and it is shown how to rigorously obtain quantum
mechanical probabilities from the classical phase space distributions resulting
from the dynamics. At short time scales, classical and quasiclassical initial
conditions lead to wrong results and only correctly quantized initial
conditions give a close agreement with an inherently quantum mechanical master
equation approach. With CO on Cu(100) as an example, we demonstrate the effect
for a system with ab initio frictional tensor and potential energy surfaces and
show that quantizing the initial conditions can have a large impact on both the
desorption probability and the distribution of molecular vibrational states
Nonradiative Recombination of Excitons in Carbon Nanotubes Mediated by Free Charge Carriers
Free electrons or holes can mediate the nonradiative recombination of
excitons in carbon nanotubes. Kinematic constraints arising from the quasi
one-dimensional nature of excitons and charge carriers lead to a thermal
activation barrier for the process. However, a model calculation suggests that
the rate for recombination mediated by a free electron is the same order of
magnitude as that of two-exciton recombination. Small amounts of doping may
contribute to the short exciton lifetimes and low quantum yields observed in
carbon nanotubes.Comment: 18 pages, 4 figures. Submitted to Physical Review
Dispersion and wavefunction symmetry in cold atoms experiencing artificial gauge fields
We analyze the single particle quantum mechanics of an atom whose dispersion
is modified by spin orbit coupling to Raman lasers. We calculate how the novel
dispersion leads to unusual single particle physics. We focus on the symmetry
of the ground state wavefunction in different potentials.Comment: 5 pages, 7 figure
Bose-Einstein Condensation in the presence of an artificial spin-orbit interaction
Bose-Einstein condensation in the presence of a synthetic spin-momentum
interaction is considered, focusing on the case where a Dirac or Rashba
potential is generated via a tripod scheme. We found that the ground states can
be either plane wave states or superpositions of them, each characterized by
their unique density distributions.Comment: 5 pages, no figure
Tensor networks and the numerical renormalization group
The full-density-matrix numerical renormalization group (NRG) has evolved as
a systematic and transparent setting for the cal- culation of thermodynamical
quantities at arbitrary temperatures within the NRG framework. It directly
evaluates the relevant Lehmann representations based on the complete basis sets
intro- duced by Anders and Schiller (2005). In addition, specific attention is
given to the possible feedback from low energy physics to high energies by the
explicit and careful construction of the full thermal density matrix, naturally
generated over a distribution of energy shells. Specific examples are given in
terms of spectral functions (fdmNRG), time-dependent NRG (tdmNRG), Fermi-Golden
rule calculations (fgrNRG), as well as the calculation of plain thermodynamic
expectation values. Furthermore, based on the very fact that, by its iterative
nature, the NRG eigenstates are naturally described in terms of matrix product
states, the language of tensor networks has proven enormously convenient in the
description of the underlying algorithmic procedures. This paper therefore also
provides a detailed introduction and discussion of the prototypical NRG
calculations in terms of their corresponding tensor networks.Comment: 20 pages, 11 figures (adapted from habilitation thesis
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