A vital goal in spintronics is the efficient electrical generation of spin currents, a pursuit that has recently focused on using antiferromagnets (AFMs) as spin current sources. It has been demonstrated that antiferromagnets with broken $PT$ symmetry (parity + time reversal) can efficiently generate longitudinal and transverse spin currents. At the same time, it has been generally thought that antiferromagnets with $PT$ symmetry ($PT$-AFMs) forbid the longitudinal spin polarization due to their spin-degenerate band structure. Here, in contrast with this common expectation, we show, using theoretical analysis based on magnetic point-group symmetry, that most $PT$-AFMs can generate longitudinal spin currents due to spin-orbit coupling. Using density-functional theory, we calculate the longitudinal spin conductivity of representative $PT$-AFMs, $L{1}_0$-MnPt and $\mathrm{M}{\mathrm{n}}_2\mathrm{Au}$ and show that its magnitude is comparable to that of their $PT$-broken counterparts. Our symmetry-enabled classification of antiferromagnets and theoretical results for the longitudinal spin conductivity in representative $PT$-AFMs expand our understanding of spin transport and show the possibility of robust spin-current generation in a broad range of spin-degenerate antiferromagnets.

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• Spin current
• Spin polarization
• Spintronics
• Antiferromagnets
• Density functional theory