Dynamic Jahn-Teller Mechanism of Superconductivity in MgB${}_2$

Abstract

We propose a novel mechanism of superconductivity in MgB${}_2$ based on the dynamic electronic structure of the $p\ddot{I}ƒ$-orbitals coupled with $e_{2g}$ phonons. A nonconventional superconducting state is found to arise frome lectron-phonon interactions in the presence of additional pairing channels made available by the dynamic Jahn-Teller effects. A partially broken pseudo-spin symmetry in this Jahn-Teller system, together with two-phonon exchange pairing, naturally gives rise to two distinct gaps both of which are basically isotropic in the ($k_x$, $k_y$) space. Important experimental observations including high $T_c$ and the anomalous specific heat are explained using this theory.