Multipole as -electron spin-charge density in filled skutterudites

Hotta, Takashi

In general, spin-orbit coupling is strong for electrons and then, spin-orbital complex degrees of freedom, i.e., , become active in -electron compounds. Due to recent advances in experimental techniques, multipole ordering phenomena have been actually observed in filled skutterudites with high symmetry. To understand multipole ordering, phenomenological theory has been developed and several experimental results could be explained, but it is necessary to make more effort to clarify microscopic aspects of multipole degrees of freedom in -electron systems. Here I propose to define -electron multipole as spin-charge density operator in one-body form from the viewpoint of multipole expansion of electron density in electromagnetism. Then, I analyze a seven-orbital Anderson model by using a numerical renormalization group method. I discuss possible multipole state of heavy lanthanide filled skutterudites.