2 research outputs found
Theory of Coulomb drag for massless Dirac fermions
Coulomb drag between two unhybridized graphene sheets separated by a
dielectric spacer has recently attracted considerable theoretical interest. We
first review, for the sake of completeness, the main analytical results which
have been obtained by other authors. We then illustrate pedagogically the
minimal theory of Coulomb drag between two spatially-separated two-dimensional
systems of massless Dirac fermions which are both away from the
charge-neutrality point. This relies on second-order perturbation theory in the
screened interlayer interaction and on Boltzmann transport theory. In this
theoretical framework and in the low-temperature limit, we demonstrate that, to
leading (i.e. quadratic) order in temperature, the drag transresistivity is
completely insensitive to the precise intralayer momentum-relaxation mechanism
(i.e. to the functional dependence of the scattering time on energy). We also
provide analytical results for the low-temperature drag transresistivity for
both cases of "thick" and "thin" spacers and for arbitrary values of the
dielectric constants of the media surrounding the two Dirac-fermion layers.
Finally, we present numerical results for the low-temperature drag
transresistivity in the case in which one of the media surrounding the
Dirac-fermion layers has a frequency-dependent dielectric constant. We conclude
by suggesting an experiment that can potentially allow for the observation of
departures from the canonical Fermi-liquid quadratic-in-temperature behavior of
the transresistivity.Comment: 20 pages, 4 figure
On Coulomb drag in double layer systems
We argue, for a wide class of systems including graphene, that in the low
temperature, high density, large separation and strong screening limits the
drag resistivity behaves as d^{-4}, where d is the separation between the two
layers. The results are independent of the energy dispersion relation, the
dependence on momentum of the transport time, and the wave function structure
factors. We discuss how a correct treatment of the electron-electron
interactions in an inhomogeneous dielectric background changes the theoretical
analysis of the experimental drag results of Ref. [1]. We find that a
quantitative understanding of the available experimental data [1] for drag in
graphene is lacking.Comment: http://iopscience.iop.org/0953-8984/24/33/335602