Cooperative Jahn-Teller effects in PrO₂

A number of features recently observed experimentally in PrO₂, such as anomalies in the magnetic excitations spectrum, the reduction of the ordered magnetic moment below the Neel temperature, the distortion of the oxygen cage and the splitting of the ground state in the paramagnetic phase, are interpreted as consequences of electron-phonon coupling and cooperative effects. A coupling to phonons with trigonal symmetry is found appropriate to describe the experimental results. While a single center model can explain the reduction of the ordered magnetic moment and also the main features of the differential cross section, a cooperative model is necessary to interpret the observed distortion of the oxygen cage and the observed splitting of the ground state into two doublets in the paramagnetic phase