Femtosecond mid-IR pump–probe spectroscopy of photoinduced insulator to metal transition in dimer Mott insulator κ-(BEDT-TTF) 2X

Abstract

Ultrafast dynamics of the photoinduced insulator (I) to metal (M) transition were investigated using femtosecond mid-infrared pump–probe spectroscopy in two-dimensional organic Mott insulators [bis (ethylenedithio)]-tetrathiafulvalene (BEDT-TTF) salts κ-(BEDT-TTF) 2X ( κ-(ET) 2X, where X denotes anion). In κ-( d-ET) 2Cu[N(CN) 2]Br, a metallic state was photogenerated using a phonon-mediated mechanism: the effective bandwidth increases through the photoinduced molecular rearrangement. The mechanism differs fundamentally from the previously reported photoinduced filling control in one-dimensional Mott insulators.