38 research outputs found
Optical phonon scattering and theory of magneto-polarons in a quantum cascade laser in a strong magnetic field
We report a theoretical study of the carrier relaxation in a quantum cascade
laser (QCL) subjected to a strong magnetic field. Both the alloy (GaInAs)
disorder effects and the Frohlich interaction are taken into account when the
electron energy differences are tuned to the longitudinal optical (LO) phonon
energy. In the weak electron-phonon coupling regime, a Fermi's golden rule
computation of LO phonon scattering rates shows a very fast non-radiative
relaxation channel for the alloy broadened Landau levels (LL's). In the strong
electron-phonon coupling regime, we use a magneto-polaron formalism and compute
the electron survival probabilities in the upper LL's with including increasing
numbers of LO phonon modes for a large number of alloy disorder configurations.
Our results predict a nonexponential decay of the upper level population once
electrons are injected in this state.Comment: 10 pages, 23 figure
Metal-to-semiconductor transition in squashed armchair carbon nanotubes
We investigate electronic transport properties of the squashed armchair
carbon nanotubes, using tight-binding molecular dynamics and Green's function
method. We demonstrate a metal-to-semiconductor transistion while squashing the
nanotubes and a general mechanism for such transistion. It is the distinction
of the two sublattices in the nanotube that opens an energy gap near the Fermi
energy. We show that the transition has to be achieved by a combined effect of
breaking of mirror symmetry and bond formation between the flattened faces in
the squashed nanotubes.Comment: 4 papges, 4 figures, to appear in Phys. Rev. Let