Vortex Pinning and Dynamics in Perovskite Oxides: Thermal Magneto-Transport in the Mixed State

Abstract

Vortex arrays have been predicted to exist in type-II superconductors by Abrikosov[1]. They are of interest, not only because of technological reasons, i.e. the possibility of blocking the critical current-decay as a function of applied magnetic field and temperature, but also because of fundamental questions pertaining to the (B,T) phase diagram description, and the types of phase transitions between the ordered (or not) phases. In the (B, T) plane, there are several lines which have been previously indicated by many authors and very recently discussed in a review paper [2]. Dating back to the time of the discovery of superconductor properties, there is the B _{c 1} line below which there is a complete flux expulsion from the sample, also called the Meissner state. After the discovery of type-II superconductors, the B _{c 2}(T) line appeared such that for B > B _{c 2} the superconducting phase disappears. In bewteen B _{c 1}and B _{c 2}, there is a so-called mixed state in which the field penetration is incomplete. The ”field penetration” is usually taken as represented by lines at the center of ”vortices” made by an electrical current of normal electrons which screen the field from the superconducting phase (or conversely). The field lines are either located at intrinsic instability points in space or are thought to be pinned on some spatial defects. The thermal fluctuations tend to depin those lines.