Experimental feasibility of complex-eigenvalue pairing in Sr2RuO4

Determine whether the complex-eigenvalue pairing state predicted for Sr2RuO4 is realized in the material, thereby establishing the feasibility of an intrinsically time-reversal-symmetry-breaking superconducting state with a complex gap function.

Background

The paper identifies a distinctive class of solutions to the frequency-dependent linearized Eliashberg equation with complex-conjugate eigenvalues. The associated inter-orbital gap functions have independently nonzero real and imaginary parts on the real-frequency axis and therefore break time-reversal symmetry intrinsically, without requiring a complex linear combination of degenerate order-parameter components.

Numerical calculations suggest that this pairing behavior can occur in Sr2RuO4 and is associated with strong Hund’s coupling. The authors nevertheless state that the material-specific feasibility of this pairing remains unresolved because the available experimental evidence is inconclusive. They note that observing a single-component nematic superconducting state that also breaks time-reversal symmetry could provide an unambiguous signature of the proposed complex-eigenvalue pairing.