Thermal Amplitude Fluctuations in Arrays of Small Josephson Junctions

Abstract

In studies on Josephson Junctions arrays (JJA), it is usually assumed that finite size effects enter only through the grain capacitance and that the amplitude of the superconducting gap is well described by the bulk Bardeeen–Cooper–Schrieber (BCS) prediction. Here, we employ path integral techniques to show analytically that for sufficiently small grains thermal fluctuations modify substantially the amplitude of the order parameter and the critical temperature of the JJA. We identify a region of sizes and temperatures for which quantum fluctuations are negligible and thermal fluctuations enhance the critical temperature of the JJA.