Impurity effects on the flux phase quantum-critical-point scenario

Impurity substitution of Zn in La-214 and (Y, Ca)-123 high-T-c superconduct ors suppresses T-c but does not affect appreciably the onset of the pseudog ap phase in the underdoped region nor optimal doping or the position of the inferred quantum critical point. Based on a 1/N expansion of the t-J model we explain these findings as well as the similar dependence on a magnetic field in terms of a quantum-critical-point scenario where a flux phase caus es the pseudogap.