The correlation between the energy gap and the pseudogap temperature in cuprates: the YCBCZO and LSHCO case

Abstract: The paper analyzes the influence of the hole density, the out-of-plane or in-plane disorder, and the isotopic oxygen mass on the zero temperature energy gap ($2\Delta\left(0\right)$) for $\rm{Y}{1-x}\rm{Ca}{x}\rm{Ba}2\left(\rm{Cu}{1-y}\rm{Zn}{y}\right){3}\rm{O}{7-\delta}$ (YCBCZO) and $\rm{La}{1.96-x}\rm{Sr}{x}\rm{Ho}{0.04}\rm{CuO}{4}$ (LSHCO) superconductors. It has been found that the energy gap is visibly correlated with the value of the pseudogap temperature ($T^{\star}$). On the other hand, no correlation between $2\Delta\left(0\right)$ and the critical temperature ($T{C}$) has been found. The above results mean that the value of the dimensionless ratio $2\Delta\left(0\right)/k_{B}T_{C}$ can vary very strongly together with the chemical composition, while the parameter $2\Delta\left(0\right)/k_{B}T^{\star}$ does not change significantly. In the paper, the analytical formula which binds the zero temperature energy gap and the pseudogap temperature has been also presented.