Carrier Concentration Dependence of the Pseudo Spin Gap Behavior in LaBa₂Cu₃O_y

Abstract

The carrier-concentration dependence of the pseudo spin gap behaviors in the optimum and the overdoped regions of the LaBa₂Cu₃O_y system has been studied by NMR. In the temperature dependences of 1/T₁T, it was observed that the spin gap behavior, which is known to exist in the underdoped region, is suppressed in the overdoped region. This seems to confirm the expectation that the spin gap behavior is specific to the underdoped region. However, LaBa₂Cu₃O_6.96, which has T_c as high as 95, K, still exhibits a clear spin-gap-like behavior. This fact suggests that the optimum hole concentration to maximize T_c does not necessarily coincide with that where the spin gap behavior disappears in this system.