Raman study of carrier-overdoping effects on the gap in high-Tc superconducting cuprates

TL;DR

This study uses Raman scattering to explore how heavy overdoping affects the superconducting gap in high-Tc cuprates, revealing s-wave mixing and Coulomb screening effects that are common across these materials.

Contribution

It demonstrates that s-wave mixing occurs with overdoping in high-Tc cuprates, independent of crystal symmetry changes, and highlights the impact on the superconducting gap structure.

Findings

Electronic pair-breaking peaks shift to lower energies in overdoped cuprates.

Evidence of s-wave mixing into the d-wave order parameter.

Universal feature of s-wave mixing in high-Tc cuprates regardless of crystal symmetry.

Abstract

Raman scattering in the heavily overdoped (Y,Ca)Ba_2Cu_3O_{7-d} (T_c = 65 K) and Bi_2Sr_2CaCu_2O_{8+d} (T_c = 55 K) crystals has been investigated. For the both crystals, the electronic pair-breaking peaks in the A_{1g} and B_{1g} polarizations were largely shifted to the low energies close to a half of 2Delta_0, Delta_0 being the maximum gap. It strongly suggests s-wave mixing into the d-wave superconducting order parameter and the consequent manifestation of the Coulomb screening effect in the B_{1g}-channel. Gradual mixing of s-wave component with overdoping is not due to the change of crystal structure symmetry but a generic feature in all high-T_c superconducting cuprates.