Origin of the R-ion effect on Tc in RBa2Cu3O7

Abstract

${\mathit{T}}_{\mathit{c}}$ and ${\mathit{dT}}_{\mathit{c}}$/dP have been systematically measured for fully oxygenated R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (R-123) with R=Yb, Tm, Ho, Dy, Gd, Sm, and Nd. ${\mathit{T}}_{\mathit{c}}$ has been observed to increase from 88 to 94 K with increasing radius of the R ion (r) from 0.98 to 1.12 Å. Based on the lattice strains and our ${\mathit{dT}}_{\mathit{c}}$/dP data, we have calculated ${\mathit{T}}_{\mathit{c}}$ for the series of R-123 and compared them with the measured ${\mathit{T}}_{\mathit{c}}$. Good agreement between the experimental and the calculated results strongly suggests that the R effect on ${\mathit{T}}_{\mathit{c}}$ in R-123 originates from the strain-induced charge redistribution between the charge reservoir and the ${\mathrm{CuO}}_2$ plane.