Theory ofBi2Sr2CaCu2

Abstract

Takano et al. ͓Phys. Rev. B 65, 140513 ͑2002͒; J. Low Temp. Phys. 131, 533 ͑2003͔͒ made Josephson junctions from single crystal whiskers of Bi 2 Sr 2 CaCu 2 O 8ϩ␦ crossed an angle 0 about the c axis. From the mesa structures that formed at the cross-whisker interface, they inferred a critical current density J c ( 0 ). As with the single crystal results of Li et al. ͓Phys. Rev. Lett. 83, 4160 ͑1999͔͒, we show that the whisker data are unlikely to result from a predominantly d-wave order parameter. However, unlike the single crystals, these results, if correct, require the whisker c-axis transport to be coherent.

Bi2212 c-Axis Twist Bicrystal and Artificial and Natural Cross-Whisker Josephson Junctions: Strong Evidence for s-Wave Superconductivity and Incoherent c-Axis Tunneling

“…More recently, the J J c (45 • ) data on several junctions are non-vanishing, and consistent with each other [16]. In addition, HRTEM for two ACWJ's indicated flat junctions, and Fraunhofer and Shapiro step analyses for one φ 0 = 45 • ACWJ demonstrated the tunneling to be weak and first order [14,16]. J J c (φ 0 ) was also independent of T for 4.2 K ≤ T ≤ 60 K [16].…”

“…However, the current-voltage (I − V) characteristics showed irregular branching, suggesting a complicated recrystallization of the interface region [13,15]. The larger junction resistance R(T, 60 • ) for T c ≤ T ≤ 105 K than above 105 K also suggests an extra insulating interface barrier [14,15]. More recently, the J J c (45 • ) data on several junctions are non-vanishing, and consistent with each other [16].…”

“…3 [13]. Fits to these data indicated that the OP at 4.2 K is most likely predominantly s-wave, but the c-axis quasiparticle tunneling would have to be coherent [14]. However, the current-voltage (I − V) characteristics showed irregular branching, suggesting a complicated recrystallization of the interface region [13,15].…”

Josephson (001) tilt grain boundary junctions of high-temperature superconductors

“…If this scenario proves to be true, then further calculations with a mixed s-and d-wave OP would be warranted. 20 With regard to the most-studied material, YBCO, in addition to the two CuO 2 layers, there is also a conducting CuO chain layer, which is responsible for the orthorhombicity and the strong twinning that occurs in thin films. The strong twinning makes (100) and (010) films indistinguishable, which can complicate the analysis.…”

“…13,14,15,16,17 More recently, three Bi2212 c-axis twist Josephson junction experiments showed that the OP has at least a substantial, and possibly a dominant s-wave component for T up to the transition temperature T c . 4,18,19,20,21 Here we search for a reason for these qualitative differences. 4 To date, most theoretical treatments of in-plane (001) tilt grain boundary (GB) junctions either used the Ginzburg-Landau (GL) approach, 22 or assumed a circular in-plane Fermi surface (FS) cross-section, and that the FS-restricted d x 2 −y 2 -wave OP ∝ cos(2φ k ).…”