Loop currents from nonunitary chiral d-wave superconductivity

We consider a tight-binding model of chiral d-wave superconductivity on the honeycomb lattice. The nearest-neighbour pairing ensures a nontrivial sublattice structure for the pairing potential. We demonstrate this implies an even parity nonunitary superconducting state, extending the concept of nonunitarity beyond odd-parity pairing states. The nonunitarity is manifested in the opening of a topological mass gap at the Dirac points, similar to that in Haldane’s model of the quantum anomalous Hall state. The mass gap results from the presence of loop current correlations, which also ensures the existence of a finite Hall conductivity. Finally, in addition to the usual chiral d-wave edge states, we show that there can exist an electron-like edge resonance that originates from the topological mass gap.