Lattice distortion induced by Jahn-Teller centres

Abstract

An investigation is made of the strain field induced by Jahn-Teller (JT) centres in crystals. The approximation method which the authors employ in order to obtain the distortion pattern near the centre is based on variationally-constructed effective modes, which provide the best single-effective-frequency description of the coupling. A group-theoretical analysis is presented which classifies in some standard manner the phonon coordinates according to the irreducible representations of the point group at the impurity site. For each frequency, only one particular mode becomes coupled with the JT impurity; it is shown how this coupled mode, as well as the remaining uncoupled ones, can be obtained once a standard classification is available. The method is demonstrated for impurities with orbital doublet electronic states in cubic symmetry using simplified lattice models, and the possibility of experimental verification of the results by ENDOR is discussed.