Inherent Spin Density Wave Instability in Heavy-Fermion Superconductors

Abstract

We have demonstrated an inherent instability of unconventional anisotropic superconducting (SC) states toward the spin density wave (SDW) formation on the reason why these SC states are stabilized. Within a mean field approximation for a simplified model including the on-site repulsive and attractive interactions, we examine the competition between the SDW and various types of the p- and d-pairing states and find that to classify types of the competition, the symmetry property of the SC order parameter under translation of a nesting vector is important in addition to the symmetry of parity. We also discuss relative stability of various pairing states in the presence of the SDW. It is interpreted that the second transition observed in (U_1−xTh_x)Be₁₃ (x=2∼4 at%) is the SDW transition out of an unconventional pairing state.