Anomalous Behavior near T_c and Synchronization of Andreev Reflection in Two-Dimensional Arrays of SNS Junctions

We have investigated low-temperature transport properties of two-dimensional arrays of superconductor--normal-metal--superconductor (SNS) junctions. It has been found that in two-dimensional arrays of SNS junctions (i) a change in the energy spectrum within an interval of the order of the Thouless energy is observed even when the thermal broadening far exceeds the Thouless energy for a single SNS junction; (ii) the manifestation of the subharmonic energy gap structure (SGS) with high harmonic numbers is possible even if the energy relaxation length is smaller than that required for the realization of a multiple Andreev reflection in a single SNS junction. These results point to the synchronization of a great number of SNS junctions. A mechanism of the SGS origin in two-dimensional arrays of SNS junctions, involving the processes of conventional and crossed Andreev reflection, is proposed.