Quantum phase transitions in one-dimensional long Josephson junction stacks in parallel magnetic fields

We report the effect of quantum and thermal fluctuations on stability of mutual phase locking in one-dimensional long Josephson junction devices, involving layered superconductors. Accounting for both the induction coupling and the charging effect, we determined the zero-temperature (T=0) phase diagram, using renormalization-group analysis, and found that the in-phase mode is stable, but some out-of-phase modes are unstable against quantum fluctuations. At finite T, all stable phase-locking modes (at T=0) are unstable, but stability is still maintained within a finite length, which decreases inversely with T. In Bi2Sr2CaCu2O8+y, this length for the in-phase mode is roughly 1000 mum at 1 K.