title: Scanning tunneling spectroscopy in the superconducting state and vortex cores of the beta-pyrochlore KOs2O6.
abstract: We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (T(c)=9.6 K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31-40 A, in agreement with the value derived from the upper critical field H(c2). We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported.
authors.affiliation: DPMC-MaNEP, Université de Genève, Quai Ernest-Ansermet 24, Genève 4, Switzerland. duboisc@mit.edu
authors.forename: C
authors.initials: C
authors.lastname: Dubois
authors.forename: G
authors.initials: G
authors.lastname: Santi
authors.forename: I
authors.initials: I
authors.lastname: Cuttat
authors.forename: C
authors.initials: C
authors.lastname: Berthod
authors.forename: N
authors.initials: N
authors.lastname: Jenkins
authors.forename: A P
authors.initials: AP
authors.lastname: Petrović
authors.forename: A A
authors.initials: AA
authors.lastname: Manuel
authors.forename: O
authors.initials: O
authors.lastname: Fischer
authors.forename: S M
authors.initials: SM
authors.lastname: Kazakov
authors.forename: Z
authors.initials: Z
authors.lastname: Bukowski
authors.forename: J
authors.initials: J
authors.lastname: Karpinski