3 research outputs found
Nonlinear acoustic and microwave absorption in disordered semiconductors
Nonlinear hopping absorption of ultrasound and electromagnetic waves in
amorphous and doped semiconductors is considered. It is shown that even at low
amplitudes of the electric (or acoustic) field the nonlinear corrections to the
relaxational absorption appear anomalously large. The physical reason for such
behavior is that the nonlinear contribution is dominated by a small group of
close impurity pairs having one electron per pair. Since the group is small, it
is strongly influenced by the field. An external magnetic field strongly
influences the absorption by changing the overlap between the pair components'
wave functions. It is important that the influence is substantially different
for the linear and nonlinear contributions. This property provides an
additional tool to extract nonlinear effects.Comment: correction : misspelled name in references correcte
Images and nonlocal vortex pinning in thin superfluid films
For thin films of superfluid adsorbed on a disordered substrate, we derive
the equation of motion for a vortex in the presence of a random potential
within a mean field (Hartree) description of the condensate. The compressible
nature of the condensate leads to an effective pinning potential experienced by
the vortex which is nonlocal, with a long range tail that smoothes out the
random potential coupling the condensate to the substrate. We interpret this
nonlocality in terms of images, and relate the effective potential governing
the dynamics to the pinning energy arising from the expectation value of the
Hamiltonian with respect to the vortex wavefunction.Comment: 19 pages, revtex, to appear Phys. Rev.