Broken rotational symmetry on the Fermi surface of a high-T$_\mathrm{c}$ superconductor

TL;DR

This study provides direct evidence of broken fourfold rotational symmetry on the Fermi surface of an underdoped high-Tc superconductor, linking it to Fermi surface reconstruction and suggesting a universal feature among unconventional superconductors.

Contribution

First direct observation of C4 symmetry breaking on the Fermi surface in a high-Tc cuprate, revealing its role in Fermi surface reconstruction and universality in unconventional superconductors.

Findings

Anisotropic interlayer magnetoresistance indicates broken C4 symmetry.

Fermi surface exhibits C2 symmetry consistent with a uniaxial density-wave phase.

Supports the universality of symmetry breaking in unconventional superconductors.

Abstract

Broken fourfold rotational (C$_4$) symmetry is observed in the experimental properties of several classes of unconventional superconductors. It has been proposed that this symmetry breaking is important for superconducting pairing in these materials, but in the high superconducting transition temperature (high-T$_{\mathrm{c}}$) cuprates this broken symmetry has never been observed on the Fermi surface. We have measured a pronounced anisotropy in the angle dependence of the interlayer magnetoresistance of the underdoped high-T$_{\mathrm{c}}$) superconductor YBa$_2$Cu$_3$O$_{6.58}$, directly revealing broken C$_4$ symmetry on the Fermi surface. Moreover, we demonstrate that this Fermi surface has C$_2$ symmetry of the type produced by a uniaxial or anisotropic density-wave phase. This establishes the central role of C$_4$ symmetry breaking in the Fermi surface reconstruction of YBa$_2$Cu$_3$O$_{6+\delta}$, and suggests a striking degree of universality among unconventional superconductors.