  Antiferromagnetic spintronics actively introduces new principles of magnetic
memory, in which the most fundamental spin-dependent phenomena, i.e.
anisotropic magnetoresistance effects, are governed by an antiferromagnet
instead of a ferromagnet. A general scenario of the antiferromagnetic
anisotropic magnetoresistance effects mainly stems from the magnetocrystalline
anisotropy related to spin-orbit coupling. Here we demonstrate magnetic field
driven contour rotation of the fourfold anisotropic magnetoresistance in bare
antiferromagnetic Sr2IrO4/SrTiO3 (001) thin films hosting a strong spin-orbit
coupling induced Jeff=1/2 Mott state. Concurrently, an intriguing minimal in
the magnetoresistance emerges. Through first principles calculations, the
band-gap engineering due to rotation of the Ir isospins is revealed to be
responsible for these emergent phenomena, different from the traditional
scenario where relatively more conductive state was obtained usually when
magnetic field was applied along the magnetic easy axis. Our findings
demonstrate a new efficient route, i.e. via the novel Jeff=1/2 state, to
realize controllable anisotropic magnetoresistance in antiferromagnetic
materials.
