  Antiferromagnets are beneficial for future spintronic applications due to
their zero magnetic moment and ultrafast dynamics. But gaining direct access to
their antiferromagnetic order and identifying the properties of individual
magnetic sublattices, especially in thin films and small-scale devices, remains
a formidable challenge. So far, the existing read-out techniques such as
anisotropic magnetoresistance, tunneling anisotropic magnetoresistance, and
spin-Hall magnetoresistance, are even functions of sublattice magnetization and
thus allow us to detect different orientations of the N\'eel order for
antiferromagnets with multiple easy axes. In contrast direct electrical
detection of oppositely oriented spin states along the same easy axes (e.g., in
uniaxial antiferromagnets) requires sensitivity to the direction of individual
sublattices and thus is more difficult. In this study, using spin Seebeck
effect, we report the electrical detection of the two sublattices in a uniaxial
antiferromagnet Cr2O3. We find the rotational symmetry and hysteresis behavior
of the spin Seebeck signals measured at the top and bottom surface reflect the
dierction of the surface sublattice moments, but not the N\'eel order or the
net moment in the bulk. Our results demonstrate the important role of interface
spin sublattices in generating the spin Seebeck voltages, which provide a way
to access each sublattice independently, enables us to track the full rotation
of the magnetic sublattice, and distinguish different and antiparallel
antiferromagnetic states in uniaxial antiferromagnets.
