20,045 research outputs found
The Fractional Quantum Hall States of Dirac Electrons in Graphene
We have investigated the fractional quantum Hall states for the Dirac
electrons in a graphene layer in different Landau levels. The relativistic
nature of the energy dispersion relation of the electrons in the graphene
significantly modifies the inter-electron interactions. This results in a
specific dependence of the ground state energy and the energy gaps for
electrons on the Landau level index. For the valley-polarized states, i.e. at
\nu =1/m, m being an odd integer, the energy gaps have the largest values in
the n=1 Landau level. For the valley-unpolarized states, e.g., for the 2/3
state, the energy gaps are suppressed for the n=1 Landau level as compared to
the n=0 level. For both the n=1 and n=0 Landau levels the ground state of the
2/3 system is fully valley-unpolarized.Comment: accepted for publication in Phys. Rev. Let
Influence of disorder and a parallel magnetic field on a Quantum Cascade Laser
The luminescence spectra of a quantum cascade laser in a strong magnetic
field is influenced significantly by the presence of disorder (charged or
neutral) in the system. An externally applied magnetic field parallel to the
electron plane causes a red shift of the luminescence peak in the absence of
any disorder potential. Our results indicate that the disorder potential tends
to cancel that red shift and causes a rapid decrease of the luminescence peak.
A similar behavior was observed in a recent experiment on QCL in a parallel
magnetic field.Comment: 3 pages, 3 figue
Magnetic field induced luminescence spectra in a quantum cascade laser
We report on our study of the luminescence spectra of a quantum cascade laser
in the presence of an external magnetic field tilted from the direction
perpendicular to the electron plane. The effect of the tilted field is to allow
novel optical transitions because of the coupling of intersubband-cyclotron
energies. We find that by tuning the applied field, one can get optical
transitions at different energies that are as sharp as the zero-field
transitions.Comment: 4 pages (LaTex format), 3 figures (postscript
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