Theory of Interplay of Nuclear Magnetism and Superconductivity in AuIn2

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The recently reported coexistence of a magnetic order, with the critical temperature Tₘ=35 μ*K, and superconductivity, with the critical temperature Tₛ=207 m*K, in AuIn₂ is studied theoretically. It is shown that superconducting (S) electrons and localized nuclear magnetic moments (LM's) interact dominantly via the contact hyperfine (EX) interaction, giving rise to a spiral (or domain-like) magnetic order in superconducting phase. The electromagnetic interaction between LM's and S electrons is small compared to the EX one giving minor contribution to the formation of the oscillatory magnetic order. In clean samples (l>ξ₀) of AuIn₂ the oscillatory magnetic order should produce a line of nodes in the quasiparticle spectrum of S electrons giving rise to the power law behavior. The critical field Hc(T=0) in the coexistence phase is reduced by factor two with respect to its bare value.