  Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics
driven by the advantages of antiferromagnets producing no stray fields and
exhibiting ultrafast magnetization dynamics. The efficient method to detect an
AFM order parameter, known as the N\'eel vector, by electric means is critical
to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear
AFM metals, such as Mn3Sn, exhibit a momentum dependent spin polarization which
can be exploited in AFM tunnel junctions to detect the N\'eel vector. Using
first-principles calculations based on density functional theory, we predict a
tunneling magnetoresistance (TMR) effect as high as 300% in AFM tunnel
junctions with Mn3Sn electrodes, where the junction resistance depends on the
relative orientation of their N\'eel vectors and exhibits four non-volatile
resistance states. We argue that the spin-split band structure and the related
TMR effect can also be realized in other non-collinear AFM metals like Mn3Ge,
Mn3Ga, Mn3Pt, and Mn3GaN. Our work provides a robust method for detecting the
N\'eel vector in non-collinear antiferromagnets via the TMR effect, which may
be useful for their application in AFM spintronic devices.
