Dielectric hysteresis in van der Waals solids due to the formation of negative ion resonances

Electron resonances (i.e.. transient anions) in the gas phase are usually f ound in both elastic and inelastic electron-scattering channels of atoms an d molecules, whereas their solid-phase counterparts are observed exclusivel y in inelastic channels. Fano and collaborators originally attributed this effect to a dielectric hysteresis phenomenon, i.e., the electronic polariza tion of the surrounding medium induced by the formation of a transient anio n in a solid causes a small displacement of the atoms or molecules from the ir lattice positions, which do not have time to relax during autoionization of the anion. Thus, the resulting multiphonon excitations replace the elas tic decay channel. Experimental and theoretical evidence of this phenomenon is given for electron-resonance scattering from several crystalline van de r Waals solids.