Scanning SQUID microscope tests of the symmetry of the high-T c gap

TLDR: In this paper, the half-integer flux quantum effect in rings, disks, and blanket films of the high-Tc cuprate superconductors was observed to have sign changes consistent with d-wave symmetry.

Abstract: Direct observations of the half-integer flux quantum effect in rings, disks, and blanket films of the high-Tc cuprate superconductorsY Ba 2 Cu 3O 7−δ (YBCO),GdBa 2 Cu 3O 7−δ (GdBCO),Tl 2 Ba 2 CuO 6+δ (Tl2201), andBi 2 Sr 2 CaCu 2O 8+δ (BSCCO) with three tricrystal substrate geometries show that their gaps have sign changes consistent with d-wave symmetry. The blanket geometry gives the Josephson penetration depth directly, and provides a means for symmetry tests without patterning. Tl2201 is a tetragonal, single-layer, cuprate without chains. When combined with photoemission results, our BSCCO results imply that the gap followsd x 2−y2 symmetry closely. Asymmetric 45 degree bicrystal grain boundary samples show spontaneous magnetization, as expected for d-wave superconductors with interface roughness.