There have been many experimental studies of the superconductor
insulator transition taking place, for example, in metallic films
as the film thickness is changed, or in semiconductor films as
oxygen impurity concentration is changed. Theoretical work
has largely focused on bosonic models, assuming that these
experimental systems might contain preformed Cooper pairs
which then achieve phase coherence as the degree of disorder is
reduced. A crucial question has been what happens in
interacting, disordered fermion models.
We used Quantum Monte Carlo to study the low temperature phases
of the disordered Hubbard model with attractive
interaction. We found a transition
from a superconducting to an insulating ground state with
increasing randomness, and determined the phase diagram as a function
of interaction and disorder strengths. The critical disorder showed a
maximum at intermediate $U$, suggesting the possibility of
a cross-over between
separate fermi and bose insulating states.
``Superconductor-Insulator Transition in a Disordered Electronic System,''
N. Trivedi, R. T. Scalettar, and M.
Randeria, Phys. Rev. B54, 3756 (1996).
"Evolution of the Density of States Gap in
a Disordered Superconductor",
C. Huscroft and R.T. Scalettar,
Phys. Rev. Lett. 81, 2775 (1998).
"Quantum Monte Carlo Study of the Disordered, Attractive Hubbard Model",
R.T. Scalettar, N. Trivedi, C. Huscroft, and M. Randeria,
Phys. Rev. B59, 4364 (1999).