Quasiparticle Tunnelling and Field-Dependent Critical Current in 2212-BSCCO.pdf

a r X i v : c o n d - m a t / 0 0 0 2 2 4 6 v 1 [ c o n d - m a t .s u p r - c o n ] 1 6 F e b 2 0 0 0 1 Intrinsic C-Axis Tunnelling in BSCCO Crystals C. E. Gough, P.J. Thomas, J.C. Fenton and G. Yang a ? aSuperconductivity Research Group, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom Intrinsic c-axis tunnelling in the superconducting state has been measured in zero and finite fields in small mesa structures fabricated on the surface of 2212-BSCCO single crystals. The temperature dependence of the zero-field critical current and quasi-particle conductance is related to microscopic d-wave models in the presence of impurity scattering. The strong field dependence of the c-axis critical current provides information on the correlation of flux pancakes across adjacent superconducting bi-layers. An instability in the IV characteristics is observed below 20K, which accounts for the apparent drop in critical current at low temperatures previously reported. 1. Introduction Measurements of c-axis tunnelling across ad- jacent superconducti-+ng bi-layers in highly anisotropic cuprate superconductors, such as 2212-BSCCO, provide important information about the tunnelling of superconducting pairs and thermally excited quasi-particles. In a field, the decrease in critical current can be related to the misalignment of flux pancakes across adjacent su- perconducting bi-layers. In this paper, we con- sider both the quasiparticle conductance and the field dependence of the critical current. 2. Measurements Measurements have been made on small mesa structures, typically, shown schematically in the inset of figure 1, 20 × 20μm and ～10 nm in height corresponding to a linear array of intrin- sic Josephson junctions [1]. Measurements have been made on a number of mesas on slightly un- derdoped (#1), near optimally doped (#2) and slightly overdoped (#3) 2212-BSCCO crystals, as described along with experimental details in [2] In zero-field we observe the fam