title: Glasslike two-level systems in minimally disordered mixed crystals.
abstract: THz spectroscopy is used to identify a broad distribution of two-level systems, characteristic of glasses, in the substitutional monatomic mixed crystal systems, Ba(1-x)Ca(x)F(2) and Pb(1-x)Ca(x)F(2). In these minimally disordered systems, two-level behavior, which was not previously known to occur, begins at a specific CaF(2) concentration. The concentration dependence, successfully modeled using the statistics of the impurity distribution in the lattice, points to a collective dopant tunneling mechanism.
authors.affiliation: Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Wrubel
authors.forename: B E
authors.initials: BE
authors.lastname: Hubbard
authors.forename: N I
authors.initials: NI
authors.lastname: Agladze
authors.forename: A J
authors.initials: AJ
authors.lastname: Sievers
authors.forename: P P
authors.initials: PP
authors.lastname: Fedorov
authors.forename: D I
authors.initials: DI
authors.lastname: Klimenchenko
authors.forename: A I
authors.initials: AI
authors.lastname: Ryskin
authors.forename: J A
authors.initials: JA
authors.lastname: Campbell