  Electric currents carrying a net spin polarization are widely used in
spintronics, whereas globally spin-neutral currents are expected to play no
role in spin-dependent phenomena. Here we show that, in contrast to this common
expectation, spin-independent conductance in compensated antiferromagnets and
normal metals can be efficiently exploited in spintronics, provided their
magnetic space group symmetry supports a non-spin-degenerate Fermi surface. Due
to their momentum-dependent spin polarization, such antiferromagnets can be
used as active elements in antiferromagnetic tunnel junctions (AFMTJs) and
produce a giant tunneling magnetoresistance (TMR) effect. Using RuO$_{2}$ as a
representative compensated antiferromagnet exhibiting spin-independent
conductance along the [001] direction but a non-spin-degenerate Fermi surface,
we design a RuO$_{2}$/TiO$_{2}$/RuO$_{2}$ (001) AFMTJ, where a globally
spin-neutral charge current is controlled by the relative orientation of the
N\'eel vectors of the two RuO$_{2}$ electrodes, resulting in the TMR effect as
large as ~500%. These results are expanded to normal metals which can be used
as a counter electrode in AFMTJs with a single antiferromagnetic layer or other
elements in spintronic devices. Our work uncovers an unexplored potential of
the materials with no global spin polarization for utilizing them in
spintronics.
