title: Vortex redistribution below the first-order transition temperature in the beta-pyrochlore superconductor KOs2O6.
abstract: A miniature Hall-sensor array was used to detect magnetic induction locally in the vortex states of the beta-pyrochlore superconductor KOs2O6. Below the first-order transition at T{p} approximately 8 K, which is associated with a change in the rattling motion of K ions, the lower critical field and the remanent magnetization both show a distinct decrease, suggesting that the electron-phonon coupling is weakened below the transition. At high magnetic fields, the local induction shows an unexpectedly large jump at T{p} whose sign changes with position inside the sample. Our results demonstrate a novel redistribution of vortices whose energy is reduced abruptly below the first-order transition at T{p}.
authors.affiliation: Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan and Laboratoire des Solides Irradiés, Ecole Polytechnique, 91128 Palaiseau Cedex, France.
authors.forename: T
authors.initials: T
authors.lastname: Shibauchi
authors.forename: M
authors.initials: M
authors.lastname: Konczykowski
authors.forename: C J
authors.initials: CJ
authors.lastname: van der Beek
authors.forename: R
authors.initials: R
authors.lastname: Okazaki
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuda
authors.forename: J
authors.initials: J
authors.lastname: Yamaura
authors.forename: Y
authors.initials: Y
authors.lastname: Nagao
authors.forename: Z
authors.initials: Z
authors.lastname: Hiroi