Plastic crystals, melting, and random fields

Abstract

Listen

Translate article

A simple microscopic hamiltonian is proposed to describe the phase diagram of molecular crystals which exhibit a plastic phase. Translational and rotational degrees of freedom are represented by two Ising systems coupled linearly. In addition an external random field is coupled to the rotational degrees of freedom. Two regimes are obtained. In the first regime, translational degrees of freedom are quenched and act as local uniform fields on the rotational degrees of freedom. There exists a competition with the external random fields. In the second regime rotational degrees of freedom quenched in a disorder state act as local random fields on translational long range order. The model provides a unified description of various experimental results and is supported by some numerical simulations.