Broken fourfold rotational 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-temperature cuprates this broken symmetry has never been observed on the Fermi surface. Now, using measurements performed in 45 tesla at the edge of the superconducting regime, a team from the US and the UK (including Paul Goddard at Warwick) have found a pronounced anisotropy in the angle-dependent interlayer magnetoresistance of underdoped YBa2Cu3O6.58. Fourfold symmetry on the Fermi surface is revealed to be broken in a manner consistent with a uniaxial or anisotropic density-wave phase.

• Caption to Figures: Polar plot of the interlayer magnetoresistance taken at 15 K and 45 T as a function of field inclination and in-plane angle.
• Publication: npj Quantum Materials 2, Article number: 8 (2017)
• DOI: 10.1038/s41535-017-0013-z