Excitation-Photon-Energy Selectivity of Photoconversions in Halogen-Bridged Pd-Chain Compounds: Mott Insulator to Metal or Charge-Density-Wave State

Ultrafast photoinduced transitions of a one-dimensional Mott insulator into two distinct electronic phases, metal and charge-density-wave (CDW) state, were achieved in a bromine-bridged Pd-chain compound [Pd(en)(2)Br](C-5-Y)(2)H2O (en = ethylenediamine and C-5-Y = dialkylsulfosuccinate), by selecting the photon energy of a femtosecond excitation pulse. For the resonant excitation of the Mott-gap transition, excitonic states are generated and converted to one-dimensional CDW domains. For the high-erenergy excitation, free electron and hole carriers are produced, giving rise to a transition of the Mott insulator to a metal. Such selectivity in photoconversions by the choice of initial photoexcited states opens a new possibility for the developments of advanced optical switching and memory functions.