Measurements of Delta and UF from Andreev reflections and McMillan-Rowell oscillations in edge junctions of YBa2Cu3O6.6/YBa2Cu2.55Fe0.45Oy/YBa2Cu3O6.6

摘要

We report measurements of dynamic resistance of high quality oxygen deficient SNS edge junctions with YBa2Cu3O6.6 (T-c=60 K) as the superconductor (S) and YBa2Cu2.55Fe0.45Oy as the barrier (N). Below the gap a series of peaks in the dynamic resistance is identified as due to multiple Andreev reflections in the barrier (V-n=2 Delta/en), while above the gap, the peaks are attributed to McMillan-Rowell oscillations (Delta V = h upsilon(F)'/4ed(N)). Analysis of the subgap series in the 60 K YBa2Cu3O6.6 yields a gap value Delta(a-b) of 16 +/- 1.5 meV, and a coupling constant 2 Delta/kT(c) of 6.2 +/- 0.5. The McMillan-Rowell series yield the renormalized Fermi velocity of quasiparticles in the barrier upsilon(F)' = ( 1.5 +/- 0.1) x 10(7) cm/sec. [S0163-1829(99)15233-0]. [References: 22]