In-plane current-voltage characteristics and oscillatory Josephson-vortex flow resistance in La-freeBi2+xSr2−xCuO

Abstract

We have investigated the in-plane I-V characteristics and the Josephson-vortex flow resistance in highquality La-free Bi 2+x Sr 2−x CuO 6+␦ ͑Bi-2201͒ single crystals in parallel and tilted magnetic fields at temperatures down to 40 mK. For parallel magnetic fields below the resistive upper critical field H c2 ‫ء‬ , the I-V characteristics obey a power law with a smooth change with increasing magnetic field of the exponent from above 5 down to 1. In contrast to the double-layer cuprate Bi-2212, the observed smooth change suggests that there is no change in the mechanism of dissipation ͑no Kosterlitz-Thouless transition͒ over the range of temperatures investigated. At small angles between the applied field and the ab plane, prominent current steps in the I-V characteristics and periodic oscillations of Josephson-vortex flow resistance are observed. While the current steps are periodic in the voltage at constant fields, the voltage position of the steps, together with the flux-flow voltage, increases nonlinearly with magnetic field. The ab-flow resistance oscillates as a function of field with a constant period over a wide range of magnetic fields and temperatures. The current steps in the I-V characteristics and the flow resistance oscillations can be linked to the motion of Josephson vortices across layers.

Intrinsic Josephson junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2

“…This periodic modulation of the out-of-plane flux-flow voltage upon increasing a well-aligned in plane field is a hallmark of intrinsic Josephson behavior. Such oscillatory effects have been extensively studied experimentally in cuprate intrinsic Josephson compounds 6,11,21,22 and their origin has been well identified theoretically as a result of a periodic modulation of the surface barrier due to vortex matching effects 23,24 . For magnetic fields well aligned with the superconducting layers, vortices in an iJJ system are purely of Josephson character without any Abrikosov-like segments ("pancake vortices") in the superconducting layers.…”