Reminder: tomorrow's seminar at 11:30 hrs

[Condensed_Matter_Group]

SEMINAR on     Disorder and strong electron correlations


Thursday, 15 March -  11:30 a.m.



Luigi Stasi Seminar Room,  Leonardo Building - first floor



Boris NAROZHNY   ( Karlsruhe Institute of Technology )



" Coulomb drag in graphene "


Abstract


We study the effect of Coulomb drag between two closely positioned
graphene monolayers.  In the limit of weak electron-electron interaction
and small inter-layer spacing the drag is described by a universal
function of the chemical potentials of the layers measured in the units of
temperature.  When both layers are tuned close to the Dirac point (i.e.
when both chemical potentials are much smaller than temperature), then the
drag coefficient is proportional to the product of the chemical
potentials.  In the opposite limit of low temperature the drag is
inversely proportional to the product of the chemical potentials.  In the
mixed case where the chemical potentials of the two layers belong to the
opposite limits we find that the drag coefficient is proportional to the
smaller chemical potential and inverse proportional to the larger.  For
stronger interaction and larger values of the inter-layer spacing the drag
coefficient acquires logarithmic corrections and can no longer be
described by a power law.  Further logarithmic corrections are due to the
energy dependence of the impurity scattering time in graphene (if both
chemical potentials are much larger than temperature, then  these are
small and may be neglected). In the case of strongly doped (or gated)
graphene (i.e. when the chemical potential are much larger than the
inverse inter-layer spacing) the drag coefficient acquires additional
dependence on the inter-layer spacing and we recover the usual
Fermi-liquid result if the screening length is smaller than the spacing.