Jahn-Teller effects in paramagnetic crystals

Subgroups and Homology of Free Products of Profinite Groups

“…The tetrahedral configuration is described by Bates (1978, figure 1) and collective coordinates, defined in terms of local displacements at each of the ions, are listed in his table 6. In terms of the conventional cubic axes (as attached to the central ion in the figure referred to) the collective coordinates are as shown in table 1.…”

Physical laws and the numerical values of fundamental constants

“…The coexistence of these two sorts of spectrum in the same material presents a paradox: the broad band following the phonon density of states suggests a coupling of the Cu2-wavefunctions to the phonon modes which spreads more or less uniformly over the entire band width, while a calculation of the hindered rotation spectrum is normally done in terms of a single mode of vibration with a well defined frequency. The difficulty of reconciling many-mode models of the Jahn-Teller interaction with calculations using only a single mode had been recognised long before, and a lot of work has been done in developing transformations between the two models (see Bates (1978) for a survey and references), but because experiments are necessarily on impurities it is always possible to argue that the local environment is so different from the crystal as a whole that perhaps the single interacting mode in the calculation is a genuine local mode taking part in the Jahn-Teller interaction, and the modes of the bulk of the crystal do not participate at all. The importance of the Guha and Chase work M C M O ' B r i e n is that it demonstrates experimentally that many-mode and single-mode effects can be seen in the same material and associated with the same impurity.…”

An analysis of the T⊗(e+e) two-mode Jahn-Teller system with strong coupling

“…At low temperatures and in the absence of perturbation such as spin-orbit coupling, the system will be frozen into one of the lowest energy wells in the potential energy surface, so we can perform the unitary transformation (14) with (15) where a In are the free parameters corresponding to Gin coordinates. The transformation displaces the origin of each of the effective displacements qln by -liR ln [2].…”

“…The calculation techniques have been considerably generalized and applied to describe the experimental spectra of impurity centers in many systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Vibronic effects also playa role in other phenomena as phase transitions and ferroelectricity [4,15,16].…”