  Antiferromagnets may exhibit spin superfluidity since the dipole interaction
is weak. We seek to establish that this phenomenon occurs in insulators such as
NiO, which is a good spin conductor according to previous studies. We
investigate nonlocal spin transport in a planar antiferromagnetic insulator
with a weak uniaxial anisotropy. The anisotropy hinders spin superfluidity by
creating a substantial threshold that the current must overcome. Nevertheless,
we show that applying a high magnetic field removes this obstacle near the
spin-flop transition of the antiferromagnet. Importantly, the spin
superfluidity can then persist across many micrometers, even in dirty samples.
