Spin superfluidity in noncollinear antiferromagnets*

Spin superfluidity is very promising for applications as it allows long-distance spin transport in magnetic systems. So far superfluidity has been observed in collinear antiferromagnets. We extend the description of spin superfluidity to noncollinear antiferromagnets (nAFMs) and explore various realizations in exchange interaction dominated hexagonal antiferromagnets. We find that the system in the long-wavelength regime is described by a nonlinear sigma model with additional corrections from Dzyaloshinskii-Moriya interactions and anisotropies. We find that the system approximately holds a U(1)-rotational symmetry associated with spin superfluidity. The power-law spatial decay signature of spin decay is identified in a nonlocal-measurement setup. We also discuss the generalization of mixing conductance to noncollinear systems and spin current injection into nAFM. Our simple theory can help in designing and interpreting experiments on spin superfluidity in nAFM. We suggest iron jarosites as promising material candidates for realizing our proposal.