title: Fermi surface and order parameter driven vortex lattice structure transitions in twin-free YBa2Cu3O7.
abstract: We report on small-angle neutron scattering studies of the intrinsic vortex lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8 T. Because of the suppressed pinning to twin-domain boundaries, a new distorted hexagonal VL structure phase is stabilized at intermediate fields. It is separated from a low-field hexagonal phase of different orientation and distortion by a first-order transition at 2.0(2) T that is probably driven by Fermi surface effects. We argue that another first-order transition at 6.7(2) T, into a rhombic structure with a distortion of opposite sign, marks a crossover from a regime where Fermi surface anisotropy is dominant, to one where the VL structure and distortion is controlled by the order-parameter anisotropy.
authors.affiliation: School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.
authors.forename: J S
authors.initials: JS
authors.lastname: White
authors.forename: V
authors.initials: V
authors.lastname: Hinkov
authors.forename: R W
authors.initials: RW
authors.lastname: Heslop
authors.forename: R J
authors.initials: RJ
authors.lastname: Lycett
authors.forename: E M
authors.initials: EM
authors.lastname: Forgan
authors.forename: C
authors.initials: C
authors.lastname: Bowell
authors.forename: S
authors.initials: S
authors.lastname: Strässle
authors.forename: A B
authors.initials: AB
authors.lastname: Abrahamsen
authors.forename: M
authors.initials: M
authors.lastname: Laver
authors.forename: C D
authors.initials: CD
authors.lastname: Dewhurst
authors.forename: J
authors.initials: J
authors.lastname: Kohlbrecher
authors.forename: J L
authors.initials: JL
authors.lastname: Gavilano
authors.forename: J
authors.initials: J
authors.lastname: Mesot
authors.forename: B
authors.initials: B
authors.lastname: Keimer
authors.forename: A
authors.initials: A
authors.lastname: Erb