Two-component uniform spin susceptibility in superconducting HgBa$_{2}$CuO$_{4+\delta}$ single crystals determined with $^{63}$Cu and $^{199}$Hg NMR

TL;DR

This study uses $^{63}$Cu and $^{199}$Hg NMR to reveal a two-component behavior of spin susceptibility in HgBa$_{2}$CuO$_{4+\delta}$ superconductors, showing different temperature dependencies linked to pseudogap and superconductivity.

Contribution

It provides the first detailed NMR analysis demonstrating a two-component uniform spin susceptibility in HgBa$_{2}$CuO$_{4+\delta}$, clarifying the roles of pseudogap and doping.

Findings

The pseudogap-related component decreases from room temperature without a sharp transition.

A second, temperature-independent component vanishes below the superconducting transition.

The second component increases with doping and constitutes a significant part of the total susceptibility.

Abstract

$^{63}$Cu and $^{199}$Hg NMR shifts for an optimally and underdoped HgBa$_{2}$CuO$_{4+\delta}$ single crystal are reported, and the temperature dependence dictates a two-component description of the uniform spin susceptibility. The first component, associated with the pseudogap phenomenon in the NMR shifts, decreases already at room temperature and continues to drop as the temperature is lowered, without a drastic change at the transition temperature into the superconducting state. The second component is temperature independent above the superconducting transition temperature and vanishes rapidly below it. It increases with doping and is a substantial part of the total spin susceptibility measured at both nuclei.