Speaker
Kenji Yonemitsu
(Institute for Molecular Science)
Description
Photoexcitations cause phase transitions from different types of insulators to metals in organic compounds. Their ultrafast dynamics are theoretically studied on the basis of electron-phonon-coupled wave functions in extended Holstein-Peierls-Hubbard models on anisotropic triangular lattices. We focus on 2D 1/4-filled-band charge-ordered insulators, \theta-(BEDT-TTF)2RbZn(SCN)4 and \alpha-(BEDT-TTF)2I3, which have similar Coulomb-driven charge orders and quite different photoinduced dynamics.
On picosecond timescales, couplings with inter-molecular lattice phonons are evident. In the \theta compound, the charge order is quickly recovered after photoexcitation because molecular rotations stabilize the charge order in a stripe-by-stripe manner. In the \alpha compound, the charge order is easily melted to create a macroscopic metallic domain because inter-molecular lattice phonons have much weaker effects [1].
On ten-femtosecond timescales, couplings with intra-molecular vibrations are evident. In the \alpha compound, a coherent oscillation of correlated electrons and subsequent Fano destructive interference with intra-molecular vibrations have been observed, which are well reproduced by calculations based on exact many-electron-phonon wave functions [2].
[1] Y. Tanaka and K. Yonemitsu, JPSJ 79, 034708 (2010).
[2] Y. Kawakami et al., PRL 105, 246402 (2010).
Author
Kenji Yonemitsu
(Institute for Molecular Science)
Co-authors
Nobuya Maeshima
(Institute of Materials Science, University of Tsukuba)
Yasuhiro Tanaka
(Institute for Molecular Science)
