Fractional Quantized Vortices as Direct Evidence of dx2-y2 -Wave Pairing Symmetry up to Critical Temperature in High-Tc Cuprate Superconductors

Abstract

The detection of the fractional vortices at asymmetric bicrystal boundaries in Bi2Sr2CaCu2O8+y (BSCCO) and YBa2Cu3O7-y (YBCO) thin films using a scanning superconducting quantum interference device (SQUID) microscope (SSM) is reported. The measurements are performed from 3 K to 90 K and the unconventional fractional vortices are found to exist up to the local critical temperature TJc at the Josephson boundary. The results provide the evidence of dx2-y2 symmetry of superconducting order parameter up to TJc , and the observed fractional vortices under different bicrystal geometries are explained by the Sigrist-Rice Josephson current formula based on the dx2-y2 -wave pairing symmetry.