title: Femtosecond resolution of soft mode dynamics in structural phase transitions.
abstract: The microscopic pathway along which ions or molecules in a crystal move during a structural phase transition can often be described in terms of a collective vibrational mode of the lattice. In many cases, this mode, called a "soft" phonon mode because of its characteristically low frequency near the phase transition temperature, is difficult to characterize through conventional frequency-domain spectroscopies such as light or neutron scattering. A femtosecond time-domain analog of light-scattering spectroscopy called impulsive stimulated Raman scattering (ISRS) has been used to examine the soft modes of two perovskite ferroelectric crystals. The low-frequency lattice dynamics of KNbO(3) and BaTiO(3) are clarified in a manner that permits critical evaluation of microscopic models for their ferroelectric transitions. The results illustrate the advantages of ISRS over conventional Raman spectroscopy of low-frequency, heavily damped soft modes.
authors.forename: T P
authors.initials: TP
authors.lastname: Dougherty
authors.forename: G P
authors.initials: GP
authors.lastname: Wiederrecht
authors.forename: K A
authors.initials: KA
authors.lastname: Nelson
authors.forename: M H
authors.initials: MH
authors.lastname: Garrett
authors.forename: H P
authors.initials: HP
authors.lastname: Jensen
authors.forename: C
authors.initials: C
authors.lastname: Warde