Investigation of impurity effects in La2−xSrxCu1−yMyO4 (M=Ga,Zn) by electronic specific heat

Abstract

The electronic specific heat Cel was studied at T≤10K on Ga- and Zn-doped La2−xSrxCuO4 (0.16≤x≤0.22). In pure La2−xSrxCuO4 (0.16≤x≤0.22), the Cel at T<Tc contains only a T2 component but no T-linear one, which is peculiar to a clean d-wave superconductor. Partial substitution of Ga or Zn for Cu changes the T2-term of Cel into a quite different one described by the sum of a T-linear and a nearly T3 term. The coefficient of the T-linear term, γ, markedly increases with Zn-or Ga-content. The λ/λN vs. Tc/Tco relation for Zn-doped samples with x≥0.2 is in good agreement with the theoretical curve for resonant impurity scattering in a d-wave superconductor, while those for Ga-doped samples and for Zn-doped samples with x<0.2 deviate slightly from the theoretical curve. Such a deviation will be discussed in relation to the change in the magnetic properties of the present system caused by impurity-doping.