Investigation of impurity effects in La(2-x)Sr(x)Cu(1-y)M(y)O(4) (M=Ga,Zn) by electronic specific heat

The electronic specific heat C-cl was studied at T less than or equal to 10K on Ga- and Zn-doped La2-xSrxCuO4 (0.16 less than or equal to x less than or equal to 0.22). In pure La2-xSrxCuO4 (0.16 less than or equal to x less than or equal to 0.22), the C-cl at T much less than T-c contains only a T-2 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 T-2-term of C-cl into a quite different one described by the sum of a T-linear and a nearly T-3 term. The coefficient of the T-linear term, gamma, markedly increases with Zn- or Ga-content. The gamma/gamma(N) vs. T-C/T-C0, relation for Zn-doped samples with x greater than or equal to 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.