Crossover of the dynamical regime of the spt in A-TCNB under hydrostatic pressure

Abstract

Anthracene-TCNB is a weak charge-transfer molecular crystal which presents a second order phase transition. At atmospheric pressure, a soft mode has been observed by inelastic neutron scattering in the high temperature phase. Under hydrostatic pressure, the transition remains continuous whereas a drastic change occurs in the dynamical regime. At 3 kbar, at the superlattice point, the soft mode-type scattering is indeed replaced by a quasielastic response. This feature indicates a continuous crossover from a displacive regime to an order-disorder regime for a modest pressure of 1.5 kbar.