Weak coupling approach to magnetic and orbital susceptibilities for superconducting states in multiorbital electron-phonon coupled model

Abstract: Alkali-doped fullerides are molecular-based superconductors with multiple active orbitals. In this paper, using the Eliashberg theory with the retardation effect of Jahn-Teller phonons, we study the response of the spin-singlet superconducting state relevant to fulleride materials. The spin Zeeman field is not active for the singlet pairing state, and the magnetic orbital field, which physically generates a circular electron motion inside the fullerene molecule, is also shown to be inactive. On the other hand, the electric orbital (or quadrupolar) field, which corresponds to a uniaxial distortion, remains active across the superconducting phase transition. This is understood by the orbital-symmetric structure of the Cooper pair, which is susceptible to the electric orbital field, while it is not the case for the magnetic orbital field which tends to create an antisymmetric part.