Nernst effect in the cuprate superconductor YBCO: Broken rotational and translational symmetries

TL;DR

This study investigates the evolution of Nernst effect anisotropy in YBCO, revealing a transition from rotational to translational symmetry breaking linked to Fermi surface reconstruction and electronic nematic-to-smectic transition.

Contribution

It demonstrates the temperature-dependent suppression of Nernst anisotropy due to Fermi surface changes, highlighting a sequence of symmetry breaking in cuprate superconductors.

Findings

Nernst anisotropy vanishes at zero temperature.

Emergence of a high-mobility electron pocket at low temperature.

Sequence of symmetry breaking from rotational to translational.

Abstract

The Nernst coefficient of the cuprate superconductor YBa2Cu3Oy was recently shown to become strongly anisotropic within the basal plane when cooled below the pseudogap temperature T*, revealing that the pseudogap phase breaks the four-fold rotational symmetry of the CuO2 planes. Here we report on the evolution of this Nernst anisotropy at low temperature, once superconductivity is suppressed by a magnetic field. We find that the anisotropy drops rapidly below 80 K, to vanish in the T=0 limit. We show that this loss of anisotropy is due to the emergence of a small high-mobility electron-like pocket in the Fermi surface at low temperature, a reconstruction attributed to a low-temperature state that breaks the translational symmetry of the CuO2 planes. We discuss the sequence of broken symmetries - first rotational, then translational - in terms of an electronic nematic-to-smectic transition such as could arise when unidirectional spin or charge modulations order. We compare YBa2Cu3Oy with iron-pnictide superconductors where the process of (unidirectional) antiferromagnetic ordering gives rises to the same sequence of broken symmetries.