Fermi Surface Meets Multipoles in Skutterudites

In many trivalent filled skutterudites physical properties are characterized by the nesting property of the main Fermi surface and the mutipole orderings. The main conduction band consists of Pnictogen p-orbitals with the symmetry of xyz, and the Fermi surface shows a good nesting property with q = (1, 0, 0). The Coulomb potential up to the sixth order term can couple with such the Pnictogen molcular orbital, as it is the third order term symmetry xyz. Therefore, the orbital multipoles up to rank 6 (hexacontatetrapole moment), originating in 4f electrons affect the main conduction band in the filled skutterudites. Anti-ferromagnetically (q = (1, 0, 0)) higher multipole ordering can be assisted by the Fermi surface nesting, to open a gap at the Fermi level, as typically realized in PrRu4P12. In other many skutterudites, there exist other Fermi surfaces to suppress the anti-ferromagnetically ordering, however multipole moments may change the Fermi surface volumes, because it affects only the main conduction band. The coupling between the xyz molcular orbital and the multipole degrees of freedom is the key issue to understand a variety of physical properties realized in the filled skutterudites.