Abstract
Dynamics of photoinduced phase transitions in molecular conductors are reviewed from the perspective of interplay between correlated electrons and phonons. (1) The charge-transfer complex TTF-CA shows a transition from a neutral paraelectric phase to an ionic ferroelectric phase. Lattice phonons promote this photoinduced transition by preparing short-range lattice dimerization as a precursor. Molecular vibrations stabilize the neutral phase so that the ionic phase, when realized, possesses a large ionicity and the Mott character; (2) The organic salts θ-(BEDT-TTF)2RbZn(SCN)4 and α-(BEDT-TTF)2I3 show transitions from a charge-ordered insulator to a metal. Lattice phonons make this photoinduced transition hard for the former salt only. Molecular vibrations interfere with intermolecular transfers of correlated electrons at an early stage; (3) The organic salt κ-(d-BEDT-TTF)2Cu[N(CN)2]Br shows a transition from a Mott insulator to a metal. Lattice phonons modulating intradimer transfer integrals enable photoexcitation-energy-dependent transition pathways through weakening of effective interaction and through introduction of carriers.
Highlights
Most of organic conductors are recognized as strongly correlated electron systems, which show a variety of electronic phases depending on temperature T, pressure P, constituent elements, etc
From the perspective of interplay between intra- and inter-molecular degrees of freedom and interplay among correlated electrons, lattice phonons and molecular vibrations, we review the following photoinduced phase transitions realized in molecular conductors
Collective motion of electron transfers is observed and it interferes with molecular vibrations; (3) The Mott insulator phase in κ-(d-BEDT-TTF)2 Cu[N(CN)2 ]Br can be converted into a metallic phase by photoexcitation
Summary
Most of organic conductors are recognized as strongly correlated electron systems, which show a variety of electronic phases depending on temperature T , pressure P , constituent elements, etc. Molecules, the building blocks of molecular conductors, are large objects and the intermolecular overlaps are generally small, so that the ratios of on-site Coulomb energies to the transfer integrals are large compared with those in transition-metal oxides This makes electrons correlated strongly with each other. Collective motion of electron transfers is observed and it interferes with molecular vibrations; (3) The Mott insulator phase in κ-(d-BEDT-TTF) Cu[N(CN)2 ]Br can be converted into a metallic phase by photoexcitation This transition is induced by the weakening of effective interaction relative to the bandwidth or the introduction of carriers away from half filling. Both transition pathways are realized by tuning the energy of photoexcitation, using intradimer and interdimer charge-transfer excitations in the dimer-Mott insulator phase
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