Quantum effects on the BKT phase transition of two-dimensional Josephson arrays

The phase diagram of two-dimensional Josephson arrays is studied by means o f the mapping to the quantum XY model. The quantum effects on the thermodyn amics of the system can be evaluated with quantitative accuracy by a semicl assical method, the pure-quantum self-consistent harmonic approximation, an d those of dissipation can be included in the same framework by the Caldeir a-Leggett model. Within this scheme, the critical temperature of the superc onductor-metal transition, which is a Berezinskii-Kosterlitz-Thouless one, can be calculated in an extremely easy way as a function of the quantum cou pling and of the dissipation mechanism. Previous quantum Monte Carlo result s for the same model appear to be rather inaccurate, while a comparison wit h experimental data leads us to conclude that the commonly assumed dissipat ion model is not suitable to describe in detail a real system.