  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 give
a large effect high temperatures. The two key differences between optical and
acoustic phonon mediated drag are: (1) the optical phonon mediated interlayer
interaction is short-ranged due to their negligible group velocity at the
Brillouin zone center; and (2) 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.
