Frustration and lattice effects on photoinduced melting of charge orders in quasi-two-dimensional organic conductors

Abstract

Quasi-two-dimensional organic conductors θ ‐ ( BEDT ‐ TTF ) 2 RbZn ( SCN ) 4 and α ‐ ( BEDT ‐ TTF ) 2 I 3 [BEDT-TTF= bis(ethylenedithio)tetrathiafulvalene] are known to have quite similar charge-ordered ground states with so-called horizontal stripes. Their photoinduced dynamics toward conductive states are quite different and their mechanisms are theoretically studied by numerical solutions to the time-dependent Schrödinger equation for the exact many-electron wave functions coupled with classical phonons in extended Peierls–Hubbard models on anisotropic triangular lattices. The θ - type salt has a highly symmetric crystal structure and its triangular lattice induces charge frustration, which is relieved by molecular rotations in the charge-ordered state. The lattice effect is thus strong and the large lattice stabilization energy makes the charge order hard, compared with that in the α - type salt. The different structural symmetries are reflected in their photoinduced evolutions of ground-state populations and charge distributions.