Electron-like Fermi surface and in-plane anisotropy due to chain states in YBa$_2$Cu$_3$O$_{7-\delta}$ superconductors

TL;DR

This paper demonstrates that metallic chain states in YBa2Cu3O7−δ superconductors cause electron-like Fermi surfaces and in-plane anisotropic transport signals, explaining negative Hall effects and Nernst anisotropy without invoking nematic order.

Contribution

The study shows that chain states naturally produce electron-like Fermi surfaces and anisotropic transport properties, providing an alternative explanation to nematic phases in YBCO.

Findings

Chain states induce electron-like Fermi surfaces across doping levels.

Negative Hall effect arises from chain-dominated transport in underdoped YBCO.

In-plane Nernst anisotropy explained by chain-induced quasi-uniaxiality.

Abstract

We present magneto-transport calculations for YBa$_2$Cu$_3$O$_{7-\delta}$ (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 `quasi-uniaxial' metallic chain state. Finally, we comment on how the chain state can also lead to electron-like quantum oscillations.