Critical point and the nature of the pseudogap of single-layered copper-oxide Bi$_{2}$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta}$ superconductors

TL;DR

This study investigates the pseudogap phase in single-layered cuprate superconductors under high magnetic fields, revealing its termination at a critical doping level and its coexistence with superconductivity.

Contribution

It identifies the critical doping point where the pseudogap phase ends and demonstrates the coexistence of pseudogap and superconductivity in these materials.

Findings

Pseudogap persists in overdoped region but terminates at doping ~0.21.

Normal state becomes Fermi liquid beyond the critical doping.

Substantial Fermi surface remains in the pseudogap state.

Abstract

We apply strong magnetic fields of H=28.5 \sim 43 T to suppress superconductivity (SC) in the cuprates Bi_{2}Sr_{2-x}La_xCuO_{6+\delta} (x=0.65, 0.40, 0.25, 0.15 and 0), and investigate the low temperature (T) normal state by ^{63}Cu nuclear spin-lattice relaxation rate (1/T_1) measurements. We find that the pseudogap (PG) phase persists deep inside the overdoped region but terminates at x \sim 0.05 that corresponds to the hole doping concentration of approximately 0.21. Beyond this critical point, the normal state is a Fermi liquid characterized by the T_1T=const relation. A comparison of the superconducting state with the H-induced normal state in the x=0.40 (T_c = 32 K) sample indicates that there remains substantial part of the Fermi surface even in the fully-developed PG state, which suggests that the PG and SC are coexisting matters.