Extending Universal Nodal Excitations Optimizes Superconductivity in Bi2Sr2CaCu2O8+d

TL;DR

This study reveals that in Bi2Sr2CaCu2O8+d, the universal d-wave nodal excitation spectrum correlates with the superconducting transition temperature, and optimizing the Fermi surface coverage enhances superconductivity.

Contribution

It uncovers a doping-independent universal nodal spectrum and links the extent of this universal behavior to the superconducting transition temperature in cuprates.

Findings

Universal d-wave nodal spectrum observed across different Tcs.

Superconducting Tc correlates with the Fermi surface fraction exhibiting the universal spectrum.

Overdoping and temperature increase disrupt the universal nodal behavior.

Abstract

Understanding the mechanism by which d-wave superconductivity in the cuprates emerges and is optimized by doping the Mott insulator is one of the major outstanding problems in condensed matter physics. Our high-resolution scanning tunneling microscopy measurements of the high transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+d show that samples with different Tcs in the low doping regime follow a remarkably universal d-wave low energy excitation spectrum, indicating a doping independent nodal gap. We demonstrate that Tc instead correlates with the fraction of the Fermi surface over which the samples exhibit the universal spectrum. Optimal Tc is achieved when all parts of the Fermi surface follow this universal behavior. Increasing temperature above Tc turns the universal spectrum into an arc of gapless excitations, while overdoping breaks down the universal nodal behavior.