SPring-8, the large synchrotron radiation facility

Date&Time: 13:30-15:00, 16 April, 2004

Speaker: Dr. Keiichirou Nasu
Affiliation: Institute of Materials Structure Science, High Energy Accelerator Research Organization

Abstract
　　We will be concerned with a macroscopic parity violation and a ferro- ( or super-para-) electricity, induced by a photo-generated electrons in the perovskite type quantum dielectric . This photogenerated electron in the 3d band of Ti, is assumed to couple, weakly but quadratically with soft-anharmonic phonons. It is also assumed to couple strongly but linearly to the breathing ( or ) type high energy phonons. These two types of electron-phonon couplings result in two types of polarons, a "super-para-electric large polaron" with a quasi-global parity violation, and an "off-center type self-trapped polaron" with only a local parity violation. This super-para-electric large polaron, being equal to a charged and conductive ferroelectric domain, greatly enhances both the quasi-static electric susceptibility and the electronic conductivity. This theory also well agrees with recent experiments on photo-induced inner core inelastic x-ray scatterings, photo-induced infrared absorptions, photo-electron emission spectra and luminescence spectra.