11,859 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
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
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
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
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
Couplings in coupled channels versus wave functions in the case of resonances: application to the two states
In this paper we develop a formalism to evaluate wave functions in momentum
and coordinate space for the resonant states dynamically generated in a unitary
coupled channel approach. The on shell approach for the scattering matrix,
commonly used, is also obtained in Quantum Mechanics with a separable
potential, which allows one to write wave functions in a trivial way. We
develop useful relationships among the couplings of the dynamically generated
resonances to the different channels and the wave functions at the origin. The
formalism provides an intuitive picture of the resonances in the coupled
channel approach, as bound states of one bound channel, which decays into open
ones. It also provides an insight and practical rules for evaluating couplings
of the resonances to external sources and how to deal with final state
interaction in production processes. As an application of the formalism we
evaluate the wave functions of the two states in the , and other coupled channels.Comment: 23 pages, 3 figures. v2: Added a section to calculate form factor
Zitterbewegung is not an observable
It has recently been claimed that Zitterbewegung has been observed. However,
we argue that it is not an observable and that the authors' observations must
be reinterpreted
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