Why there is a difference between optimal doping for maximal Tc and critical doping for highest \rho_s in cuprate superconductors?

TL;DR

This paper explains the difference between optimal doping for maximum Tc and critical doping for highest superfluid density in cuprate superconductors using a kinetic energy driven mechanism, highlighting the role of effective and bare pair gaps.

Contribution

It introduces a theoretical explanation for the doping-dependent shift between optimal Tc and highest superfluid density based on the ratio of effective to bare pair gaps.

Findings

Coupling strength decreases with increasing doping.

Shift from critical doping for bare pair gap to optimal doping for effective pair gap.

Difference between optimal Tc and highest ho_s explained by pairing gap dynamics.

Abstract

A long-standing puzzle is why there is a difference between the optimal doping \delta_{optimal}=0.15 for the maximal superconducting (SC) transition temperature Tc and the critical doping \delta_{critical}=0.19 for the highest superfluid density \rho_s in cuprate superconductors? This puzzle is calling for an explanation. Within the kinetic energy driven SC mechanism, it is shown that except the quasiparticle coherence, \rho_s is dominated by the bare pair gap, while Tc is set by the effective pair gap. By calculation of the ratio of the effective and the bare pair gaps, it is shown that the coupling strength decreases with increasing doping. This doping dependence of the coupling strength induces a shift from the critical doping for the maximal value of the bare pair gap parameter to the optimal doping for the maximal value of the effective pair gap parameter, which leads to a difference between the optimal doping for the maximal Tc and the critical doping for the highest \rho_s.