title: New Josephson plasma modes in underdoped YBa2Cu3O6.6 induced by a parallel magnetic field.
abstract: The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured below T(c)=59 K in parallel magnetic fields H parallel CuO2 up to 7 T. Upon application of a parallel field, a new peak appears at finite frequency in the optical conductivity at the expense of suppression of c-axis condensate weight. We conclude that the dramatic change originates from different Josephson coupling strengths between bilayers with and without Josephson vortices. We find that the 400 cm(-1) broad conductivity peak in YBCO gains the spectral weight under parallel magnetic field; this indicates that the condensate weight at omega=0 is distributed to this peak as well as to the new optical Josephson mode.
authors.affiliation: Graduate School of Frontier Sciences, University of Tokyo, Hongo 7-3-1, Bunkyo, Japan. kojima@lyra.t.u-tokyo.ac.jp
authors.forename: K M
authors.initials: KM
authors.lastname: Kojima
authors.forename: S
authors.initials: S
authors.lastname: Uchida
authors.forename: Y
authors.initials: Y
authors.lastname: Fudamoto
authors.forename: S
authors.initials: S
authors.lastname: Tajima