Tunneling asymmetry in superconducting Nd_1Ba_2Cu_3O_y single crystals

摘要

Clean, Stable, and atomically flat (001) surfaces of the as-prepared Nd_1Ba_2Cu_3O_y (Nd123) single crystals have been investigated using a Low Temperature UltraHigh Vacuum Scanning Tunneling Microscope/Spectroscopy (STM/STS) system at 10 K. Several sets of highly reproducible STS data show the existence of an asymmetry in the tunneling spectra in superconducting Nd123 single crystals. The asymmetry is found to be intrinsic and can be explained by assuming that the pairing potential is a function of the kinetic energy of the charge carriers. The STS data are compared with the predictions of different theoretical models. The data on the (001) surfaces may be better fitted by assuming an S wave symmetry. Pure d(x~2 - y~2) symmetry is ruled out.