4,969 research outputs found
Magneto-optical conductivity in graphene including electron-phonon coupling
We show how coupling to an Einstein phonon affects the absorption
peaks seen in the optical conductivity of graphene under a magnetic field .
The energies and widths of the various lines are shifted, and additional peaks
arise in the spectrum. Some of these peaks are Holstein sidebands, resulting
from the transfer of spectral weight in each Landau level (LL) into
phonon-assisted peaks in the spectral function. Other additional absorption
peaks result from transitions involving split LLs, which occur when a LL falls
sufficiently close to a peak in the self-energy. We establish the selection
rules for the additional transitions and characterize the additional absorption
peaks. For finite chemical potential, spectral weight is asymmetrically
distributed about the Dirac point; we discuss how this causes an asymmetry in
the transitions due to left- and right-handed circularly polarized light and
therefore oscillatory behavior in the imaginary part of the off-diagonal Hall
conductivity. We also find that the semiclassical cyclotron resonance region is
renormalized by an effective-mass factor but is not directly affected by the
additional transitions. Last, we discuss how the additional transitions can
manifest in broadened, rather than split, absorption peaks due to large
scattering rates seen in experiment.Comment: 24 pages, 21 figure
Phonon structures in the electronic density of states of graphene in magnetic field
Unlike in ordinary metals, in graphene, phonon structure can be seen in the
quasiparticle electronic density of states, because the latter varies on the
scale of the phonon energy. In a magnetic field, quantization into Landau
levels creates even more significant variations. We calculate the density of
states incorporating electron-phonon coupling in this case and find that the
coupling has pronounced new effects: shifting and broadening of Landau levels,
creation of new peaks, and splitting of any Landau levels falling near one of
the new peaks. Comparing our calculations with a recent experiment, we find
evidence for a phonon with energy similar to but somewhat greater than the
optical mode and a coupling corresponding to a mass enhancement
parameter .Comment: 6 pages, 4 figures, final version to be published in EP
Ultrasonic attenuation in clean d-wave superconductors
We consider the attenuation of longitudinal ultrasonic waves in a clean
two-dimensional d-wave superconductor. We show that the attenuation coefficient
is linear in temperature at low temperatures for all in-plane directions of the
propagation of the ultrasound, and that the coefficient of the linear term can
be used to determine the parameters crucial for the low temperature transport
in these compounds.Comment: 4 pages, very minor changes, published versio
- …