title: Vortex fluctuations in underdoped Bi(2)Sr(2)CaCu(2)O(8+delta) crystals.
abstract: Vortex thermal fluctuations in heavily underdoped Bi(2)Sr(2)CaCu(2)O(8+delta) (T(c)=69.4 K) are studied using Josephson plasma resonance. From the zero-field data, we obtain the c-axis penetration depth lambda(L,c)(0)=230+/-10 micrometer and the anisotropy ratio gamma(T). The low plasma frequency allows us to study phase correlations over the whole vortex solid state and to extract a wandering length r(w) of vortex pancakes. The temperature dependence of r(w) as well as its increase with dc magnetic field is explained by the renormalization of the vortex line tension by the fluctuations, suggesting that this softening is responsible for the dissociation of the vortices at the first order transition.
authors.affiliation: Laboratoire des Solides Irradiés, CNRS-UMR 7642 and CEA/DSM/DRECAM, Ecole Polytechnique, 91128 Palaiseau, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Colson
authors.forename: Marcin
authors.initials: M
authors.lastname: Konczykowski
authors.forename: Marat B
authors.initials: MB
authors.lastname: Gaifullin
authors.forename: Yuji
authors.initials: Y
authors.lastname: Matsuda
authors.forename: Piotr
authors.initials: P
authors.lastname: Gierłowski
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Peter H
authors.initials: PH
authors.lastname: Kes
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Van Der Beek