Interplay of spin chirality and unconventional superconductivity

Spin chirality is well-known to play a key role in generating nontrivial Berry phases that lead to, for example, an anomalous Hall effect. This work investigates how nonvanishing spin chirality affects superconducting states, focusing on the coupling between itinerant electrons and localized spins with nonvanishing spin chirality. To demonstrate, we examine an s-d model on a geometrically frustrated lattice, in which the nontrivial real-space noncollinear spin texture of localized d-electrons promotes the formation of effective spin-triplet pairing of the itinerant electrons. This unconventional pairing arises because spin chirality breaks parity and time reversal symmetry, favoring pairing states with mixed parity and promoting spin triplet components. Furthermore, the nonvanishing spin chirality can lead to an asymmetric spin interaction between the spins of the Cooper pairs, analogous to the Dzyaloshinskii-Moriya-like interaction in magnetic systems. We solve the gap equation self-consistently to determine the superconducting order and study the effect of spin chirality on the pairing symmetry and collective spin excitations in the superconducting state.