118 research outputs found
Coulomb Drag as a Probe of Coupled Plasmon Modes in Parallel Quantum Wells
We show theoretically that the Coulomb drag rate between two parallel
quasi-two-dimensional electron gases is substantially enhanced by the coupled
acoustic and optic plasmon modes of the system at temperatures (where is the Fermi temperature) for experimentally relevant
parameters. The acoustic mode causes a sharp upturn in the scaled drag rate as
a function of temperature at . Other experimental signatures
of plasmon-dominated drag are a dependence on the well separation ,
and a peak in the drag rate as a function of relative carrier densities at
matched Fermi velocities.Comment: 10 pages, RevTeX 3.0, MIC-TH-
Plasmon enhancement of Coulomb drag in double quantum well systems
We derive an expression for the drag rate (i.e., interlayer momentum transfer
rate) for carriers in two coupled two-dimensional gases to lowest nonvanishing
order in the screened interlayer electron--electron interaction, valid for {\sl
arbitrary} intralayer scattering mechanisms, using the Boltzmann transport
equation. We calculate the drag rate for experimentally relevant parameters,
and show that for moderately high temperatures (, where
is the Fermi temperature) the dynamical screening of the interlayer results in
a large enhancement of the drag rate due to the presence of coupled plasmon
modes. This plasmon enhancement causes the scaled drag rate to have a peak (i)
as a function of temperature at , and (ii) as a function of
the ratio of densities of the carriers in the two layers when their Fermi
velocities are equal. We also show that the drag rate can be significantly
affected by the {\sl intralayer} scattering mechanisms; in particular, the drag
rate changes approximately by a factor of 2 when the dopant layer modulation
doped structures are moved in from 400~\AA to 100~\AA.Comment: RevTex, 21 pages, 7 postscript figure
Optical-phonon-induced frictional drag in coupled two-dimensional electron gases
The role of optical phonons in frictional drag between two adjacent but electrically isolated two-dimensional electron gases is investigated. Since the optical phonons in III-V materials have a considerably larger coupling to electrons than acoustic phonons (which are the dominant drag mechanism at low T and large separations), it might be expected that the optical phonons will contribute a large effect at high temperatures. The two key differences between optical-and acoustic-phonon-mediated drag are (i) the optical-phonon-mediated interlayer interaction is short-ranged due to the negligible group velocity at the Brillouin zone center, and (ii) the typical momentum transfer for an optical-phonon-mediated scattering is relatively large. These considerations make optical-phonon-mediated drag difficult to see in single-subband GaAs systems, but it may be possible to see the effect in double-subband GaAs systems or single-subband quantum wells in a material with a lower effective mass and lower optical-phonon energy, such as InSb. [S0163-1829(98)05219-9]
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