The effect of chemical doping and hydrostatic pressure on Tc of Y 1− yCa yBa 2Cu 3O x single crystals

Abstract

We performed susceptibility measurements on Y 1− y Ca y Ba 2Cu 3O x single crystals under high He pressure. For each Ca content various samples with different oxygen contents have been prepared to probe the influence of Ca on T c( x), d T c/d p( x) and T c,max. Starting from the parabolic T c( n h) behavior we calculated n h values from T c and T c,max for each sample. It is shown that in the overdoped region d T c/d p can be described by a pressure induced charge transfer with d n h/d p≈3.7 10 −3 GPa −1 and a d T c,max/d p value of 0.8 K/GPa, irrespective of the Ca content. In the underdoped region additional pressure effects lead to a peak in d T c/d p at ≈0.11 holes/CuO 2 plane. However, with increasing Ca content this peak is strongly depressed. This is explained in terms of an increasing disorder in the CuO chain system due to doping. Deviations in d T c/d p at very low n h values can be assigned to the ortho II ordering in the CuO chain system.