Superconductor-insulator quantum phase transition in a single Josephson junction

摘要

The superconductor-to-insulator quantum phase transition in resistivelyshunted Josephson junctions is investigated by means of path-integral MonteCarlo simulations. This numerical technique allows us to directly access the(previously unexplored) regime of the Josephson-to-charging energy ratiosE_J/E_C of order one. Our results unambiguously support an earlier theoreticalconjecture, based on renormalization-group calculations, that at T -> 0 thedissipative phase transition occurs at a universal value of the shuntresistance R_S = h/4e^2 for all values E_J/E_C. On the other hand,finite-temperature effects are shown to turn this phase transition into acrossover, which position depends significantly on E_J/E_C, as well as on thedissipation strength and on temperature. The latter effect needs to be takeninto account in order to reconcile earlier theoretical predictions with recentexperimental results.