Superconducting-state thermodynamic parameters of HgBa 2Ca n-1 Cu nO y ( n=1, 2, and 3)

Abstract

Magnetic measurements have been performed on magnetically aligned, nearly single-phase samples of HgBa 2CuO 4+ δ , HgBa 2 CaCu 2O 6+ δ , and HgBa 2Ca 2Cu 3O 8+ δ . The basic thermodynamic parameters describing the superconducting state, such as the penetration depth and the coherence length in the a-b-plane, and the lower and upper critical fields along the c-axis, were determined. A systematic decrease of the penetration depth in the a-b-plane, a decrease of Ginzburg-Landau parameter, and an increase in the thermodynamic critical field with increasing number of CuO 2 planes in the unit cell are revealed. The values obtained for the Ginzburg-Landau parameter and the thermodynamic critical field for the Hg-based superconductors are compared with those for YBa 2Cu 3O 7- δ . The low position of the irreversibility lines for the Hg-based superconductors is attributab le to relatively small values of the thermodynamic critical field.