Electron-like Fermi surface and in-plane anisotropy due to chain states in YBa_2Cu_3O_(7-δ) superconductors

摘要

We present magnetotransport calculations for YBa_2Cu_3O_(7-δ) (YBCO) materials to show that the electron-like metallic chain state gives both the negative Hall effect and in-plane anisotropic large Nernst signal. We show that the inevitable presence of the metallic lD CuO chain layer lying between the CuO_2 bilayers in YBCO renders an electron-like Fermi surface in the doping range as wide as p = 0.05 to overdoping. With underdoping, a pseudogap opening in the CuO_2 state reduces its hole-carrier contribution, and, therefore, the net electron-like quasiparticles dominate the transport properties, and a negative Hall resistance commences. We also show that the observation of in-plane anisotropy in the Nernst signal-which was taken as a definite evidence of the electronic "nematic" pseudogap phase-is naturally explained by including the "quasiuniaxial" metallic chain state. Finally, we comment on how the chain state can also lead to electron-like quantum oscillations.