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.
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Kirtley, J.R., Tsuei, C.C., Moler, K.A. et al. Scanning SQUID microscope tests of the symmetry of the high-T c gap. Czech J Phys 46 (Suppl 6), 3169–3176 (1996). https://doi.org/10.1007/BF02548126
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DOI: https://doi.org/10.1007/BF02548126