We study inelastic (dynamical) impurity scattering effects in two-band
superconductors with the same (s++​ wave) or different (s±​ wave) sign
order parameters. We focus on the enhancement of the superconducting transition
temperature Tc​ by magnetic interband scattering with the interchange
of crystal-field singlet ground and multiplet excited states. Either the
s++​-wave or s±​-wave state is favored by the impurity-mediated
pairing, which depends on the magnetic and nonmagnetic scattering strengths
derived from the hybridization of the impurity states with the conduction
bands. The details are examined for the singlet-triplet configuration that is
suggestive of Pr impurities in the skutterudite superconductor
LaOs4​Sb12​.Comment: 14 pages, 5 figures, to appear in J. Phys. Soc. Jpn. Vol. 79, No. 9
(2010