Electron-like Fermi surface and in-plane anisotropy due to chain states in YBa2Cu3O7-δ superconductors

We present magnetotransport calculations for YBa₂Cu₃O_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 1D CuO chain layer lying between the CuO₂ 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 CuO₂ 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.