Exciton mediated superconductivity in PrOs4Sb12

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 au conduction band, which hybridizes with a Pr4f2 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 (kxky + ωkykz + ω2kzkx, ω=e±i2π/3) is stabilized with broken time reversal symmetry. (author)