THERMODYNAMICS AND CRITICAL FIELDS OF YBA2(CU1-XNIX)(3)O-7-DELTA FROMA D-WAVE MODEL OF SUPERCONDUCTIVITY

Specific heat, penetration depth, and infrared measurements on Ni- and Zn-doped YBa2(Cu(1-x)M(x))(3)O-7-delta are shown to be consistent wit h each other within the framework of a phenomenological model in which a d-wave density of stares is broadened by the disorder associated wi th the dopant. Strong scattering from each dopant atom results in a ra pid 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 th e thermodynamic critical field H-c(T), the specific heat C(T), the ab- plane penetration depth lambda(T), the ab-plane coherence length xi(T) , and the critical fields H-c1(T) and H-c2(T) for fields applied perpe ndicular to the ab plane. C(T) and lambda(T) are compared, favorably, with measurements. xi and H-c2 have not been measured directly, so thi s paper presents the first experimental estimate of these quantities. It is found that xi(0) increases by less than 50% with increasing Ni c oncentration, even though the superfluid density, proportional to 1/la mbda(2)(0), decreases by a factor of 10.