Tailored defects in HTSC — What can we learn from swift heavy ion irradiation?

Abstract

Since the discovery of superconductivity above liquid nitrogen temperature in copper oxide based compounds many experiments have been performed on the one hand to study their mixed state properties and on the other hand to check their technological applicability. Due to their well defined cylindrical shape latent particle tracks (also known as columnar defects) are a powerful tool to investigate the mixed state in high temperature superconductors (HTSC) as they provide optimized pinning centers. Therefore in this paper we will present experiments performed with HTSC samples (epitaxial thin films on SrTiO 3 substrates, single crystals and technical tapes) containing columnar defects. We will outline the influence of these linear defects on the resistive phase transition and on transport I–V curves of YBa 2Cu 3O 7−δ (123) thin films. All HTSC known up to now exhibit a pronounced structure-related anisotropy. Hence we present magnetic and transport measurements concerning the angular dependence of the critical current in various irradiated HTSC compounds. Furthermore experiments with technical tapes of (BiPb) 2Sr 2Ca 2Cu 3O 10 (Bi2223) will be shown giving an overview of problems concerning technological applications. Finally in irradiated and nonirradiated Bi 2Sr 2CaCu 2O 8 (Bi2212) single crystals the flux line lattice is visualized via the high resolution Bitter decoration technique.