Effect of Zn substitution on the normal-state magnetoresistivity of epitaxial Y0.95Ca0.05Ba2(Cu1-xZnx)3Oy and Y0.9Ca0.1Ba2Cu3Oy films

We report measurements of the in-plane resistivity, magnetoresistivity (MR) and Hall effect of thin films of slightly under and nearly optimally doped Y_0.95Ca_0.05Ba₂(Cu_1-xZn_x)₃O_y (with x=0,0.02,0.04 ) and overdoped Y_0.9Ca_0.1Ba₂Cu₃O_y . We found that the introduction of Zn as a dopant strongly suppresses the orbital MR in the normal state. Surprisingly it can be fitted to a T^-4 law at lower temperatures where the resistivity and cotangent of the Hall angle cotθ_H are relatively constant and no longer obey the usual T¹ and T² laws, respectively. In other words, in these samples the increase in residual scattering rate produced by Zn has a stronger effect on cotθ_H than on the MR at low T . It seems that this new result requires some modification of well-known theories involving two distinct relaxation processes for transport and Hall currents.