15 research outputs found
Impact of Electron-Phonon Coupling on Near-Field Optical Spectra
The finite momentum transfer () longitudinal optical response
of graphene has a peak at an energy
. This corresponds directly to a quasiparticle peak in the
spectral density at momentum relative to the Fermi momentum . Inclusion
of coupling to a phonon mode at results, for , in
a constant electron-phonon renormalization of the bare bands by a mass
enhancement factor and this is followed by a phonon kink at
where additional broadening begins. Here we study the corresponding
changes in the optical quasiparticle peaks which we find to continue to
directly track the renormalized quasiparticle energies until is large
enough that the optical transitions begin to sample the phonon kink region of
the dispersion curves where linearity in momentum is lost in the renormalized
Dirac Fermion dispersion curves and the correspondence to a single
quasiparticle energy is lost. Nevertheless there remains in
features analogous to the phonon kinks of the
dispersion curves which are observable through variation of and .Comment: 6 pages, 5 figure
Suppression of Spontaneous Supercurrents in a Chiral p-Wave Superconductor
The superconducting state of SRO is widely believed to have chiral p-wave
order that breaks time reversal symmetry. Such a state is expected to have a
spontaneous magnetization, both at sample edges and at domain walls between
regions of different chirality. Indeed, muon spin resonance experiments are
interpreted as evidence of spontaneous magnetization due to domain walls or
defects in the bulk. However, recent magnetic microscopy experiments place
upper limits on the magentic fields at the sample edge and surface which are as
much as two orders of magnitude smaller than the fields predicted theoretically
for a somewhat idealized chiral p-wave superconductor. We investigate the
effects on the spontaneous supercurrents and magnetization of rough and pair
breaking surfaces for a range of parameters within a Ginzburg-Landau formalism.
The effects of competing orders nucleated at the surface are also considered.
We find the conditions under which the edge currents are significantly reduced
while leaving the bulk domain wall currents intact, are quite limited. The
implications for interpreting the existing body of experimental results on
superconducting SRO within a chiral p-wave model are discussed.Comment: Changes to section 3, typos remove