Broken rotational symmetry in the pseudogap phase of a high-Tc superconductor

TL;DR

This paper demonstrates that the pseudogap phase in high-Tc cuprate superconductors intrinsically breaks four-fold rotational symmetry, suggesting stripe or nematic order as the underlying electronic state.

Contribution

It provides direct evidence of intrinsic rotational symmetry breaking in the pseudogap phase via Nernst effect anisotropy, clarifying the nature of this phase.

Findings

Large in-plane Nernst anisotropy appears at T*

Anisotropy is intrinsic to CuO2 planes, not due to lattice chains

Pseudogap phase exhibits strong four-fold rotational symmetry breaking

Abstract

The nature of the pseudogap phase is a central problem in the quest to understand high-Tc cuprate superconductors. A fundamental question is what symmetries are broken when that phase sets in below a temperature T*. There is evidence from both polarized neutron diffraction and polar Kerr effect measurements that time- reversal symmetry is broken, but at temperatures that differ significantly. Broken rotational symmetry was detected by both resistivity and inelastic neutron scattering at low doping and by scanning tunnelling spectroscopy at low temperature, but with no clear connection to T*. Here we report the observation of a large in-plane anisotropy of the Nernst effect in YBa2Cu3Oy that sets in precisely at T*, throughout the doping phase diagram. We show that the CuO chains of the orthorhombic lattice are not responsible for this anisotropy, which is therefore an intrinsic property of the CuO2 planes. We conclude that the pseudogap phase is an electronic state which strongly breaks four-fold rotational symmetry. This narrows the range of possible states considerably, pointing to stripe or nematic orders.