Multiple Andreev reflection in MgB_2/MgO/MgB_2 Josephson junctions

摘要

The current-voltage and conductance-voltage characteristics of MgB_2/MgO/MgB_2 junctions made with MgB_2 electrodes grown by hybrid physical-chemical vapor deposition were systematically analyzed. In the junctions with different sizes and critical current densities, we found excess current and subharmonic gap structure indicative of multiple Andreev reflection. An apparent link between multiple Andreev reflection and substantial Josephson current at high temperatures suggests that the barrier is dominated by high-transparency channels.