title: Spin-order driven Fermi surface reconstruction revealed by quantum oscillations in an underdoped high Tc superconductor.
abstract: We use quantum oscillation measurements to distinguish between spin and orbital components of the lowest energy quasiparticle excitations in YBa(2)Cu(3)O(6.54), each of which couple differently to a magnetic field. Our measurements reveal the phase of the observed quantum oscillations to remain uninverted over a wide angular range, indicating that the twofold spin degeneracy of the Landau levels is virtually unaltered by the magnetic field. The inferred suppression of the spin degrees of freedom indicates a spin-density wave is responsible for creation of the small Fermi surface pockets in underdoped YBa(2)Cu(3)O(6+x)--further suggesting that excitations of this phase are important contributors to the unconventional superconducting pairing mechanism.
authors.affiliation: Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, United Kingdom. suchitra@phy.cam.ac.uk
authors.forename: Suchitra E
authors.initials: SE
authors.lastname: Sebastian
authors.forename: N
authors.initials: N
authors.lastname: Harrison
authors.forename: C H
authors.initials: CH
authors.lastname: Mielke
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: G G
authors.initials: GG
authors.lastname: Lonzarich