In-plane current-voltage characteristics and oscillatory Josephson-vortex flow resistance in La-free Bi$_{2+x}$Sr$_{2-x}$CuO$_{6+\delta}$ single crystals in high magnetic fields

摘要

We have investigated the in-plane $I(V)$ characteristics and the Josephsonvortex flow resistance in high-quality La-freeBi$_{2+x}$Sr$_{2-x}$CuO$_{6+\delta}$ (Bi2201) single crystals in parallel andtilted magnetic fields at temperatures down to 40 mK. For parallel magneticfields below the resistive upper critical field $H^{*}_{c2}$, the $I(V)$characteristic obey a power-law with a smooth change with increasingmagnetic-field of the exponent from above 5 down to 1. In contrast to thedouble-layer cuprate Bi2212, the observed smooth change suggests that there isno change in the mechanism of dissipation (no Kosterlitz-Thouless transition)over the range of temperatures investigated. At small angles between theapplied field and the $ab$-plane, prominent current steps in the $I(V)$characteristics and periodic oscillations of Josephson-vortex flow resistanceare observed. While the current steps are periodic in the voltage at constantfields, the voltage position of the steps, together with the flux-flow voltage,increases nonlinearly with magnetic field. The $ab$-flow resistance oscillatesas a function of field with a constant period over a wide range of magneticfields and temperatures. The current steps in the $I(V)$ characteristics andthe flow resistance oscillations can be linked to the motion of Josephsonvortices across layers.