Unconventional Phase Shift in Spin Hall Magnetoresistance of Antiferromagnetic Insulators

heterostructures, we provide a comprehensive explanation for this intriguing phenomenon. Through a combination of angle-dependent transport measurements and first-principles calculations, we show that the SMR signal is governed by two competing mechanisms: a robust contribution originating from the antiferromagnetic Néel vector (NSMR) and a highly temperature-sensitive component arising from ferromagnet-like canted spin polorization (PSMR) which is constrained by the symmetry-allowed Dzyaloshinskii-Moriya coupling. We further reveal that the elusive phase shift stems from the rapid enhancement of the canted spin polarization at low temperatures, which fundamentally alters the symmetry of spin-current absorption. Our findings establish a unified physical framework for disentangling complex spin interactions in antiferromagnetic materials.