Exciton Mediated Superconductivity in PrOs₄Sb₁₂

Abstract

The most important character of the exotic superconductor PrOs₄Sb₁₂ is the existence of low-lying excitations (excitons) with a finite energy gap and it appears as the magnetic field-induced order above 4.5 T. We focus on the a_u conduction band, which hybridizes with a Pr 4f² state strongly, coupled to the excitons. It results in an attractive interaction between the conduction electrons. The symmetry of the superconducting order parameter is determined by dispersion relation of the exciton. For the bcc system PrOs₄Sb₁₂, a d-wave state (k_xk_y+ωk_yk_z+ω²k_zk_x, ω=e^±i2π⁄3) is stabilized with broken time reversal symmetry.