Fractional quantized vortices as direct evidence of dx2-y2-wave pairing symmetry up to critical temperature in high-Tc cuprate superconductors

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 T-Jc, at the Josephson boundary. The results provide the evidence of d(x2-y2) symmetry of superconducting order parameter up to T-Jc, and the observed fractional vortices under different bicrystal geometries are explained by the Sigrist-Rice Josephson current formula based on the d(x2-y2)-wave pairing symmetry.