Carrier-Concentration Dependence of the Pseudogap Ground State of Superconducting Bi2Sr2-xLaxCuO6+delta Revealed by 63,65Cu-Nuclear Magnetic Resonance in Very High Magnetic Fields

TL;DR

This study uses high magnetic field 63,65Cu-NMR to investigate the pseudogap ground state in Bi2Sr2-xLaxCuO6+delta, revealing a finite density of states at the Fermi level that varies with doping.

Contribution

It provides direct NMR evidence that the pseudogap ground state is metallic with a finite Fermi surface volume, and explores how this state evolves with doping.

Findings

Residual density of states decreases with doping

Pseudogap state remains metallic at low temperatures

Density of states approaches zero near the Mott insulator phase

Abstract

We report the results of the Knight shift by 63,65Cu-nuclear-magnetic resonance (NMR) measurements on single-layered copper-oxide Bi2Sr2-xLaxCuO6+delta conducted under very high magnetic fields up to 44 T. The magnetic field suppresses superconductivity completely and the pseudogap ground state is revealed. The 63Cu-NMR Knight shift shows that there remains a finite density of states (DOS) at the Fermi level in the zero-temperature limit, which indicates that the pseudogap ground state is a metallic state with a finite volume of Fermi surface. The residual DOS in the pseudogap ground state decreases with decreasing doping (increasing x) but remains quite large even at the vicinity of the magnetically ordered phase of x > 0.8, which suggests that the DOS plunges to zero upon approaching the Mott insulating phase.