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

摘要

We report the results of the Knight shift by 63,65Cu-nuclear-magneticresonance (NMR) measurements on single-layered copper-oxideBi2Sr2-xLaxCuO6+delta conducted under very high magnetic fields up to 44 T. Themagnetic field suppresses superconductivity completely and the pseudogap groundstate is revealed. The 63Cu-NMR Knight shift shows that there remains a finitedensity of states (DOS) at the Fermi level in the zero-temperature limit, whichindicates that the pseudogap ground state is a metallic state with a finitevolume of Fermi surface. The residual DOS in the pseudogap ground statedecreases with decreasing doping (increasing x) but remains quite large even atthe vicinity of the magnetically ordered phase of x > 0.8, which suggests thatthe DOS plunges to zero upon approaching the Mott insulating phase.