Nonmagnetic molecular Jahn-Teller Mott insulators

Narrow-band conductors may turn insulating and magnetic as a consequence of strong electron-electron correlation. In molecular conductors, the concomitance of a strong Jahn-Teller coupling may give rise to the alternative possibility of a nonmagnetic insulator, with or without a static cooperative Jahn-Teller distortion. In the latter case the insulator has Mott-like properties, with an interesting interplay between electron-electron repulsion and the Jahn-Teller effect, which is dynamical. We study this kind of nonmagnetic insulator in a very simple E⊗e Jahn-Teller model and we discuss its general properties in a more general context, also in connection with the insulating state of ${\mathrm{K}}_4$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_4$${\mathrm{C}}_{60}$.