Ultrafast phase control in one-dimensional correlated electron systems

One-dimensional (I D) correlated electron systems are good targets for the exploration of photoinduced phase transitions (PIPTs). This is because photocarrier generations and/or charge transfer (CT) excitations by lights can stimulate instabilities inherent to the 1D nature of electronic states through strong electron-electron interactions and electron(spin)-lattice interactions. In this paper, we review the ultrafast dynamics of three typical PIPTs observed in 1D correlated electron systems: 1) a photoinduced transition from a Mott insulator to a metal in a halogen-bridged Ni-chain compound, [Ni(chxn)(2)Br]Br-2 (chxn = cyclohexanediamine); 2) a photoinduced melting of a spin-Peierls phase in an organic CT compound, K-tetracyanoquinodimethane (TCNQ); 3) a photoinduced transition between neutral (N) and ionic (1) states in an organic CT compound, tetrathiafulvalene-p-chloranil (TTF-CA). The primary dynamics of these PIPTs are discussed on the basis of the results of fermosecond pump-probe spectroscopy.