title: Broken rotational symmetry in the pseudogap phase of a high-T(c) superconductor.
abstract: The nature of the pseudogap phase is a central problem in the effort to understand the high-transition-temperature (high-T(c)) copper oxide superconductors. A fundamental question is what symmetries are broken when the pseudogap phase sets in, which occurs when the temperature decreases below a value T*. There is evidence from measurements of both polarized neutron diffraction and the polar Kerr effect that time-reversal symmetry is broken, but at temperatures that differ significantly from one another. Broken rotational symmetry was detected from both resistivity measurements and inelastic neutron scattering at low doping, and from scanning tunnelling spectroscopy at low temperature, but showed no clear relation to T*. Here we report the observation of a large in-plane anisotropy of the Nernst effect in YBa(2)Cu(3)O(y) 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 CuO(2) planes. We conclude that the pseudogap phase is an electronic state that strongly breaks four-fold rotational symmetry. This narrows the range of possible states considerably, pointing to stripe or nematic order.
authors.affiliation: Département de Physique and RQMP, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Daou
authors.forename: J
authors.initials: J
authors.lastname: Chang
authors.forename: David
authors.initials: D
authors.lastname: Leboeuf
authors.forename: Olivier
authors.initials: O
authors.lastname: Cyr-Choinière
authors.forename: Francis
authors.initials: F
authors.lastname: Laliberté
authors.forename: Nicolas
authors.initials: N
authors.lastname: Doiron-Leyraud
authors.forename: B J
authors.initials: BJ
authors.lastname: Ramshaw
authors.forename: Ruixing
authors.initials: R
authors.lastname: Liang
authors.forename: D A
authors.initials: DA
authors.lastname: Bonn
authors.forename: W N
authors.initials: WN
authors.lastname: Hardy
authors.forename: Louis
authors.initials: L
authors.lastname: Taillefer