Measurement of Pair-Quasiparticle Interference in Josephson Tunnel Junctions

摘要

A successful program for applying the microscopic theory to the computation of the time-dependent behavior of a Josephson junction has now been developed. It was based, originally, on one due to D. MacDonald of NBS Boulder, but extensive modifications had to be made in order to bring the computation time and computer memory requirements down to levels that made it possible to deal with the kinds of problems I wished to attack. Such computations are very demanding because a junction has a long 'memory'. Its behavior at some moment is dependent on its history over a long time interval in the past. It can be shown that the length of this memory is directly related to the sharpness of the voltage jump that appears in the junction current-voltage characteristic at the gap voltage. R. Harris of NBS Boulder has pointed out that real junctions do not have as sharp a jump as theory predicts, and this implies that their memories are not as long as theory suggests. I investigated this question and found that artificially shortening the theoretical memory does indeed lead to rounding of the jump at the gap voltage. I found that the amount of shortening that is required to give a reasonable rounding is in fact enough to produce an appreciable reduction in both computation time and computer memory requirements.