Interchain coupling effects on photoinduced phase transitions between neutral and ionic phases in an extended Hubbard model with alternating potentials and an electron-lattice coupling

摘要

Dynamics of ionic-to-neutral and neutral-to-ionic phase transitions inducedby intrachain charge-transfer photoexcitations are studied in aquasi-one-dimensional extended Hubbard model with alternating potentials and anelectron-lattice coupling for mixed-stack charge-transfer complexes. Forinterchain couplings, we use electron-electron interactions previouslyestimated for TTF-CA (TTF=tetrathiafulvalene, CA=chloranil). Photoexcitation isintroduced by a pulse of oscillating electric field. The time-dependentHartree-Fock approximation is used for the electronic part, and the classicalapproximation for the lattice part. In the ionic-to-neutral transition, thetransferred charge density is a strongly nonlinear function of thephotoexcitation density, which is characterized by the presence of a threshold.With substantial interchain couplings comparable to those in TTF-CA, theinterchain correlation is strong during the transition. Neutral domains innearby chains simultaneously grow even if their nucleation is delayed byreducing the amplitude of the electric field. With weaker interchain couplings,the growing processes are in phase only when the amplitude of the electricfield is large. Thus, the experimentally observed, coherent motion of amacroscopic neutral-ionic domain boundary is allowed to emerge by suchsubstantial interchain couplings. In the neutral-to-ionic transition, bycontrast, the transferred charge density is almost a linear function of thephotoexcitation density. Interchain electron-electron interactions make thefunction slightly nonlinear, but the uncooperative situation is almostunchanged and consistent with the experimental findings.