  The role of substantial in-plane disorder (Zn) on the transport and AC
susceptibility of Y1-xCaxBa2(Cu1-yZny)3O7-delta was investigated over a wide
range of planar hole concentration, p. Resistivity, r(T), for a number of
overdoped to underdoped samples with y equals/greater than 0.055 showed clear
downturns at a characteristic temperature similar to that found at T* in
Zn-free underdoped samples because of the presence of the pseudogap. Contrary
to the widely observed behavior for underdoped cuprates at lower Zn contents
(where the pseudogap energy increases almost linearly with decreasing p in the
same way as for the Zn-free compounds), this apparent pseudogap temperature at
high Zn content showed very little or no p-dependence. It also increases
systematically with increasing Zn concentration in the CuO2 planes. This
anomalous behavior appears quite abruptly, e.g., samples with y less
than/equals 0.05 exhibit the usual T*(p) behavior. AC susceptibility of these
heavily disordered samples showed the superfluid density to be extremely low.
Magneto-transport, r(T,H), measurements are provisionally interpreted in terms
of high-strength pinning centers for vortices in these samples. We also discuss
various possible scenarios that might lead to a Zn induced pseudogap in the
cuprates.
