The c-axis transport in naturally-grown Bi₂Sr₂CaCu₂O₈₊δ cross-whisker junctions

Original · EN

We studied the c-axis transport of Bi₂Sr₂CaCu₂O₈₊δ (Bi2212) cross-whisker junctions formed by annealing ``naturally'' formed whisker junctions. These frequently appear during growth when the ab-faces of neighboring whiskers come in contact. We obtained Fraunhofer patterns of the cross-junction critical currents in a parallel magnetic field, and found a sharp increase in the quasiparticle tunneling conductance at eV=50-60 mV, indicating high junction quality. For our weak junctions, the interface critical current density is about 0.03 of the critical current density across the stack of bulk intrinsic junctions, as is the room temperature conductivity, and is independent of the twist angle, in contrast to most of the data reported on ``artificial'' cross-whisker junctions [Y. Takano et al., Phys. Rev. B 65, 140513(R) (2002)]. Our results provide strong evidence of incoherent interface tunneling and for at least a small s-wave order parameter component in the bulk of Bi2212 for T≤ Tc. They are also consistent with the bicrystal twist experiments of Li et al. [Phys. Rev. Lett. 83, 4160 (1999)].