Dynamical Jahn-Teller effect on $\mathrm{U}{\mathrm{O}}_2$

The dynamical Jahn-Teller effect on $\mathrm{U}{\mathrm{O}}_2$ is investigated within a microscopic model including crystal-field effects, magnetic exchange, and linear coupling with a localized trigonal phonon mode acting on the ${\Gamma }_5$ symmetry ground state and the ${\Gamma }_4$ symmetry excited state. Numerical calculations are performed in order to determine the ordered-magnetic moment and the differential cross section of $\mathrm{U}{\mathrm{O}}_2$ at low temperature $(T<T_N)$ following a properly implemented Lanczos recursion procedure. The Jahn-Teller coupling is found to be weak but essential to satisfactorily reproduce the experimental measurements.

Figure 1

Levels splitting produced by crystal-field and local magnetic interaction.

Figure 2

Behavior of the ordered magnetic moment at $T=4.2\mathrm{K}$ as a function of $h$ for different values of $S\left({\Gamma }_5\right)$. The other parameters are $\hslash \omega =10\mathrm{meV}$, $W=4.557\mathrm{meV}$, $x=0.875$.

Figure 3

Spectrum at $T=6.5\mathrm{K}$ for $S\left({\Gamma }_4\right)=0.47$, $\hslash \omega =10\mathrm{meV}$, $W=4.17\mathrm{meV}$, $x=0.812$.

Figure 4

Behavior of the first excited vibronic levels as a function of $S\left({\Gamma }_4\right)$. The symmetry of the dominant component in the corresponding eigenstates is indicated with a circle $\left({\Gamma }_3\right)$ or a cross $\left({\Gamma }_4\right)$.