EFFECT OF EXTERNAL CHARGES ON THE QUANTUM SUPERCONDUCTOR-INSULATOR TRANSITION IN A JOSEPHSON-JUNCTION ARRAY

We study the influence of a uniform background of external charges on the dynamics of a vortex moving in a quantum (zero temperature) Joseph son-junction array, in the limit in which the capacitance between isla nds, C-l, is much larger than the ground capacitance. For large Joseph son coupling, E(J) >> E(C) = e(2)/2C(1), we confirm the continuum limi t result for the vortex mass, both in the absence and in the presence of the external charges. Upon decreasing E(J)/E(C), the vortex mass va nishes at a critical value, which can be taken as an indicator of the superconductor-insulator phase transition. The phase diagram, as a fun ction of the external charge, is determined on the basis of a small a (a(2) = E(C)/8E(J)) expansion. We find, in particular, that external c harges significantly stabilise the superconducting phase.