Small dissimilarity in lattice distortion triggers anomalously large anisotropic magnetoresistance in manganite perovskite.

Anisotropic magnetoresistance (AMR) effects are of fundamental importance not only for providing information on spin-orbital coupling and magneto-crystalline anisotropy, but also for enabling technological applications. Here, we report an anomalous AMR effect in a prototype manganite single crystal---La$_{0.69}$Ca$_{0.31}$MnO$_{3}$. We demonstrate that the broken symmetry, through cubic to orthorhombic structural distortion in the crystal, leads to profound anisotropic magneto-transport behavior. The measured AMR behavior shows a direct correlation with the anisotropic field-tuned metal-insulator transition (MIT) in the system and can be understood via a phenomenological uniaxial anisotropy model. It is revealed that a small crystalline anisotropy can trigger a large AMR near the MIT phase boundary of the system.