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TT: Fachverband Tiefe Temperaturen

TT 8: Superconductivity - Poster Session

TT 8.5: Poster

Montag, 26. März 2007, 14:00–17:45, Poster A

Anomalous magnetic field dependence of the superconducting condensation energy in YBa₂Cu₃O₇ single crystals — •P. Popovich^1,2, C. Meingast¹, S. Tajima³, and T. Masui³ — ¹Forschungszentrum Karlsruhe, Institute for Solid-State Physics, 76021 Karlsruhe, Germany — ²Fakultät für Physik, Universität Karlsruhe, Germany — ³ISTEC, Tokyo, Japan

The anisotropic magnetostriction and thermal expansion of untwinned YBa₂Cu₃O₇ single crystals have been studied using capacitance dilatometry for H||c along all crystallographic axes. The thermodynamical analysis is possible due to the high crystal quality. The magnetostriction coefficient λ_i = 1/L_idL_i/dH (i=a,b,c) is reversible above 55 K, providing important information about the pressure dependencies of the thermodynamical critical field H_c(T).

The magnetic field dependence of the zero-temperature superconducting condensation energy is obtained by using the fact that the length (volume) difference between normal and superconducting states, L_n-L_s, provides a direct measure of the uniaxial pressure (hydrostatic pressure) dependence of the superconducting condensation energy. In conventional BCS superconductors, the superconducting condensation energy, as well as the magnitude of L_n-L_s, decreases monotonically with increasing field due to the increasing density of normal-state vortex cores. We find practically no field dependence of L_n-L_s as T approaches zero, which implies that the superconducting pairing energy is nearly field-independent in magnetic field up to 10 T.