43Ca NMR study of the doping effects in the high temperature superconductor (La1–xCax)(Ba1.75–xLa0.25+x)Cu3Oy

Abstract

The ⁴³Ca nuclear magnetic resonance is measured in the normal state of the high temperature superconductor (Ca_xLa_1–x)(Ba_1.75–xLa_0.25+x)Cu₃O_y as a function of temperature. The samples are chosen in order to compare the effect of changing the calcium and the oxygen contents in the underdoped regime. We determine the quadrupolar parameters and the Knight shift (KS). The macroscopic magnetic susceptibility is measured and used to estimate the ⁴³Ca hyperfine field. The variation of KS when increasing the calcium content does not show the signature of an increase of the doping level, contrary to what is suggested by the variation of macroscopic properties.