Bi_2 Sr_2 CaCu_2 O_{8+delta} Bicrystal c-Axis Twist Josephson Junctions: A New Phase-Sensitive Test of Order Parameter Symmetry
arXiv:cond-mat/0207700 · doi:10.1016/S0921-4526(02)02152-X
Abstract
Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)] prepared atomically clean BiSrCaCuO (BSCCO) Josephson junctions between identical single crystal cleaves stacked and twisted an angle about the c axis. For each bicrystal, the ratio of the c-axis twist junction critical current density to that across either single crystal part is unity, independent of and the ratio of junction areas. From extensive theoretical studies involving a variety of tunneling and superconducting order parameter (OP) forms, we conclude that the results provide strong evidence for incoherent c-axis tunneling and that the dominant OP is s-wave for . Recently, Takano {\it et al.} [Phys. Rev. B {\bf 65}, 140315(R) (2002)] obtained results from BSCCO whisker twist junctions which also rule out a pure d-wave OP, but which are surprisingly suggestive of coherent c-axis tunneling form small Fermi surface hot spots.
5 pages, 11 figures, invited talk at LT23, to be published in Physica B