Interplay between Correlated Electrons and Quantum Phonons in Charge-Ordered and Mott-Insulating Organic Compounds

K. Yonemitsua,b,c, N. Maeshimad,e and Y. Tanakaa,b,c aInstitute for Molecular Science, Okazaki 444-8585, Japan bGraduate University for Advanced Studies, Okazaki 444-8585, Japan cJST, CREST, Tokyo 102-0076, Japan dInstitute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan eCenter for Computational Sciences, University of Tsukuba, Tsukuba 305-8577, Japan

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At an early stage of the photoinduced transition from an insulator to a metal in quasi-two-dimensional organic conductors, a coherent motion of electrons is observed in a charge-ordered insulator, but not so far in a Mott insulator. The mechanisms of these different photoinduced charge dynamics are theoretically studied by numerical solutions to the time-dependent Schrödinger equation for exact many-electron-phonon wave functions on small clusters of model systems. We use two-dimensional three-quarter-filled extended Holstein-Hubbard models on anisotropic triangular lattices. For a charge-ordered insulator on a lattice simplified from the structure of α-(BEDT-TTF)2I3, we indeed find a low-energy collective electronic motion coupled with quantum phonons even if the energy of photoexcitation is away from this energy. For a Mott insulator on a lattice simplified from the structure of κ-(BEDT-TTF)2X, however, such a collective motion does not appear, and quantum phonons are hardly excited.

DOI: 10.12693/APhysPolA.121.372 PACS numbers: 78.20.Bh, 71.30.+h, 71.45.Lr, 71.10.Fd