Negative and positive magnetoresistance in the itinerant antiferromagnetBaMn2Pn2(Pn= P, As, Sb, and Bi)

We report the discovery of a large-magnetoresistance (LMR) phenomenon in a family of ${\mathrm{BaMn}}₂{Pn}₂$ antiferromagnets ($Pn$ = P, As, Sb, and Bi) with parity-time symmetry. The resistivities of these materials are reduced by 60 times in magnetic fields $\mathbf{H}$, thus yielding a LMR of about $\ensuremath{-}98%$. The LMR changes systematically along with the $Pn$ elements, hinting that its origin is the spin-orbit coupling and/or $d\ensuremath{-}p$ orbital hybridization. A positive MR component emerging on top of the negative LMR at low temperatures suggests an orbital-sensitive magnetotransport as $\mathbf{H}$ suppresses the conduction of the electronlike carriers in the $d$-like band but enhances that of holelike ones in the $d\ensuremath{-}p$ hybridized band. The anisotropy of the LMR reveals that the electrical conductivity is extremely sensitive to the minute changes in the direction of the antiferromagnetic moments induced by the parity-time symmetry-breaking $\mathbf{H}$, which is perpendicular to the antiferromagnetic spin-ordered direction. We attribute the observed LMR to the nontrivial low-energy bands of ${\mathrm{BaMn}}₂{Pn}₂$ antiferromagnets, which are governed by the parity-time symmetry.