Thermodynamics and critical fields of YBa2(Cu1−xNix)3O7−δ from a d-wave model of superconductivity

Abstract

Specific heat, penetration depth, and infrared measurements on Ni- and Zn-doped YBa2(Cu1−xMx)3O7−δ are shown to be consistent with each other within the framework of a phenomenological model in which a d-wave density of states is broadened by the disorder associated with the dopant. Strong scattering from each dopant atom results in a rapid filling in of the low-energy density of states. We use the model, with scattering rates taken from the infrared reflectance and a normal-state density of states taken from the specific heat, to calculate the thermodynamic critical field Hc(T), the specific heat C(T), the ab-plane penetration depth λ(T), the ab-plane coherence length ξ(T), and the critical fields Hc1(T) and Hc2(T) for fields applied perpendicular to the ab plane. C(T) and λ(T) are compared, favorably, with measurements. ξ and Hc2 have not been measured directly, so this paper presents the first experimental estimate of these quantities. It is found that ξ(0) increases by less than 50% with increasing Ni concentration, even though the superfluid density, proportional to 1/λ2(0), decreases by a factor of 10. © 1996 The American Physical Society.

Source-reported materials — not catalogue approval

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