Conductance spectra and superconducting gap structures observed in c-axis FeSe0.3Te0.7 / Au junctions

• Main Authors: Shen, Yu-Tien, 沈育佃
• Other Authors: Chi, Cheng-Chung
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/43922176411188766905

博士 === 國立清華大學 === 物理系 === 101 === The electric transport properties of superconducting c-axis FeSe0.3Te0.7/Au (S/N) junctions, fabricated using pulsed laser deposition, have been investigated in the temperature range of 2 K to the superconducting transition temperature Tc, and in the presence of applied magnetic fields from 0 to 9 T. A large zero-bias conductance peak has always been observed in every conductance spectrum of the junctions. In addition, we have found several gap-like features. Using the extended BTK theory with the currently favored nodeless s±-wave symmetry, our conductance spectrum can be reproduced qualitatively with Δ1 = 4 meV, and Δ2 = 6 meV at 2 K in sample #1 and Δ1 = 7 meV, and Δ2 = 10.5 meV at 2 K in sample #2. Although there is an inconsistency of the gap values in FeSeTe, the relative ratio between two gaps are both 1.5, which is the same as the published ARPES data for FeSeTe samples of similar compositions. We note that the experimental conductance spectra are substantially below the one calculated in the high bias range. Furthermore, there are unaccounted conductance minima at approximately 15.4 meV (20 meV) in junction #1 (#2) whatever the cause for these conductance minima may also be the reason for the discrepancy. In addition, we have accidentally encountered an interesting Tc enhancement effect due to oxygen-annealing effect for the pulse-deposited FeSeTe thin films. The Tc of the as-grown thin film can be increased up to 3 K after an oxygen-annealing process.