Andrea Fubini

Dipartimento di Fisica, Universita' di Firenze.

ABSTRACT:
The phase diagram of two dimensional Josephson arrays is studied by means
of the mapping to the quantum XY model. The quantum effects onto the
thermodynamics of the system can be evaluated with quantitative accuracy
by a semiclassical method, the pure-quantum self-consistent harmonic
approximation, and those of dissipation can be included in the same
framework by the Caldeira-Leggett model. Within this scheme, the critical
temperature of the superconductor-metal transition, which is a
Berezinskii-Kosterlitz-Thouless one, can be calculated in an extremely
easy way as a function of the quantum coupling and of the dissipation
mechanism. Previous quantum Monte Carlo results for the same model appear
to be rather inaccurate, while the comparison with experimental data shows
a good agreement even though the experiments present a more rapid decrease
of the transition temperature for increasing values of the quantum
coupling: this could suggest that the pure quantum XY model is
insufficient to describe the behavior of this system in whole quantum
coupling region.