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

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.