Jahn-Teller Effect in theT1g4(I)State ofMn++in RbMnF3. I

Reported in this paper are the experimental results of measurements of the Jahn-Teller displacement around ${\mathrm{Mn}}^{++}$ ions of RbMn${\mathrm{F}}_3$ in the ${}_{}{}^4{}_{}{}^{}T_{1g}^{}{}_{}{}^{}\mathrm{}\left(I\right)\mathrm{}$ state of ${\mathrm{Mn}}^{++}$. Measurements and calculations of the response of the spectrum to uniaxial stress in the [100], [111], and [110] directions show that a strong $E_g$-type distortion occurs with no appreciable $T_{2g}$ displacement. A possible lower limit on the Jahn-Teller energy of 1.6 in units of $\hslash \omega$ is obtained using the trigonal-stress results. The vibronic sidebands are shown, from polarized-stress results, to follow the spin-wave sideband as their origin.