Vortex melting line and anisotropy of high-pressure-synthesized TlBa2Ca2Cu3O10−y high-temperature superconductor from third-harmonic susceptibility studies

Abstract

The fundamental and third-harmonic susceptibility response of YBa2Cu3O7−δ (YBCO) and TlBa2Ca2Cu3O10−y (Tl:1223) high-critical temperature (Tc) superconductors with preferentially oriented crystallites has been measured in various magnetic fields up to 14 T, and with very low ac field amplitude, to probe the melting transition of the vortex matter. This method does not require large single crystals, being therefore suitable for high-Tc superconductors with small crystallites, prepared with high-pressure synthesis techniques. We determine experimentally the melting line of vortices and the anisotropy factor in high-pressure-grown Tl:1223 with a high Tc of 133.5 K. Results from similar measurements on YBCO with preferentially oriented grains are consistent with both commonly accepted models of the melting line and values of the anisotropy factor, supporting the validity of our approach.