Temperature independent cuprate pseudogap from planar oxygen NMR

TL;DR

This study analyzes NMR data from cuprate superconductors, revealing a temperature-independent pseudogap at the Fermi surface that varies with doping and is consistent across different materials, impacting their electronic properties.

Contribution

It provides a comprehensive analysis of planar oxygen NMR data, establishing the existence of a universal, temperature-independent pseudogap in cuprates and relating it to doping and material inhomogeneity.

Findings

Pseudogap is temperature independent and increases with underdoping.

States above the pseudogap are Fermi liquid-like and similar across cuprates.

Pseudogap can be as large as 1500 K in underdoped systems.

Abstract

Planar oxygen nuclear magnetic resonance (NMR) relaxation and shift data from all cuprate superconductors available in the literature are analyzed. They reveal a temperature independent pseudogap at the Fermi surface, which increases with decreasing doping in family specific ways, i.e., for some materials the pseudogap is substantial at optimal doping while for others it is nearly closed at optimal doping. The states above the pseudogap, or in its absence are similar for all cuprates and doping levels, and Fermi liquid-like. If the pseudogap is assumed exponential it can be as large as about 1500 K for the most underdoped systems, relating it to the exchange coupling. The pseudogap can vary substantially throughout a material, being the cause of cuprate inhomogeneity in terms of charge and spin, and consequences for the NMR analyses are discussed. This pseudogap appears to be in agreement with the specific heat data measured for the YBaCuO family of materials, long ago. Nuclear relaxation and shift show deviations from this scenario near $T_{\mathrm{c}}$, possibly due to other in-gap states.