17 research outputs found
Hydrodynamic model for electron-hole plasma in graphene
We propose a hydrodynamic model describing steady-state and dynamic electron
and hole transport properties of graphene structures which accounts for the
features of the electron and hole spectra. It is intended for electron-hole
plasma in graphene characterized by high rate of intercarrier scattering
compared to external scattering (on phonons and impurities), i.e., for
intrinsic or optically pumped (bipolar plasma), and gated graphene (virtually
monopolar plasma). We demonstrate that the effect of strong interaction of
electrons and holes on their transport can be treated as a viscous friction
between the electron and hole components. We apply the developed model for the
calculations of the graphene dc conductivity, in particular, the effect of
mutual drag of electrons and holes is described. The spectra and damping of
collective excitations in graphene in the bipolar and monopolar limits are
found. It is shown that at high gate voltages and, hence, at high electron and
low hole densities (or vice-versa), the excitations are associated with the
self-consistent electric field and the hydrodynamic pressure (plasma waves). In
intrinsic and optically pumped graphene, the waves constitute quasineutral
perturbations of the electron and hole densities (electron-hole sound waves)
with the velocity being dependent only on the fundamental graphene constants.Comment: 11 pages, 6 figure
Radiation induced oscillations of the Hall resistivity in two-dimensional electron systems
We consider the effect of microwave radiation on the Hall resistivity in
two-dimension electron systems. It is shown that the photon-assisted impurity
scattering of electrons can result in oscillatory dependences of both
dissipative and Hall components of the conductivity and resistivity tensors on
the ratio of radiation frequency to cyclotron frequency. The Hall resistivity
can include a component induced by microwave radiation which is an even
function of the magnetic field. The phase of the dissipative resistivity
oscillations and the polarization dependence of their amplitude are compared
with those of the Hall resistivity oscillations. The developed model can
clarify the results of recent experimental observations of the radiation
induced Hall effect.Comment: 4 pages, 1 figur
Absolute Negative Conductivity in Two-Dimensional Electron Systems Associated with Acoustic Scattering Stimulated by Microwave Radiation
We discuss the feasibility of absolute negative conductivity (ANC) in
two-dimensional electron systems (2DES) stimulated by microwave radiation in
transverse magnetic field. The mechanism of ANC under consideration is
associated with the electron scattering on acoustic piezoelectric phonons
accompanied by the absorption of microwave photons. It is demonstrated that the
dissipative components of the 2DES dc conductivity can be negative
() when the microwave frequency is
somewhat higher than the electron cyclotron frequency or its
harmonics. The concept of ANC associated with such a scattering mechanism can
be invoked to explain the nature of the occurrence of zero-resistance
``dissipationless'' states observed in recent experiments.Comment: 7 pager, 2 figure
Effect of Coulomb scattering on graphene conductivity
The effect of Coulomb scattering on graphene conductivity in field effect
transistor structures is discussed. Inter-particle scattering
(electron-electron, hole-hole, and electron-hole) and scattering on charged
defects are taken into account in a wide range of gate voltages. It is shown
that an intrinsic conductivity of graphene (purely ambipolar system where both
electron and hole densities exactly coincide) is defined by strong
electron-hole scattering. It has a universal value independent of temperature.
We give an explicit derivation based on scaling theory. When there is even a
small discrepancy in electron and hole densities caused by applied gate voltage
the conductivity is determined by both strong electron-hole scattering and weak
external scattering: on defects or phonons. We suggest that a density of
charged defects (occupancy of defects) depends on Fermi energy to explain a
sub-linear dependence of conductivity on a fairly high gate voltage observed in
experiments. We also eliminate contradictions between experimental data
obtained in deposited and suspended graphene structures regarding graphene
conductivity.Comment: 4 pages, 3 figures, to be published in JETP Let