title: Fate of the peak effect in a type-II superconductor: multicriticality in the Bragg-Glass transition.
abstract: We have used small-angle neutron scattering (SANS) and ac magnetic susceptibility to investigate the global magnetic field H vs temperature T phase diagram of a Nb single crystal in which a first-order transition of Bragg-glass melting (disordering), a peak effect, and surface superconductivity are all observable. It was found that the disappearance of the peak effect is directly related to a multicritical behavior in the Bragg-glass transition. Four characteristic phase boundary lines have been identified on the H-T plane: a first-order line at high fields, a mean-field-like continuous transition line at low fields, and two continuous transition lines associated with the onset of surface and bulk superconductivity. All four lines are found to meet at a multicritical point.
authors: Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
authors: S R
authors: SR
authors: Park
authors: S M
authors: SM
authors: Choi
authors: D C
authors: DC
authors: Dender
authors: J W
authors: JW
authors: Lynn
authors: X S
authors: XS
authors: Ling