Robust Nematicity Persisting in the Normal State of Sr-doped Bi₂Se₃

Nematic superconductivity, marked by spontaneous rotational symmetry breaking, has emerged as a central theme in topological materials such as Sr_xBi₂Se₃. Theoretical models attribute this state to a two-component E_u pairing that couples to lattice anisotropy and spin-orbit interaction, while recent studies suggest that vestigial nematicity may persist slightly above critical temperature T_c due to superconducting fluctuations. Yet, evidence for a robust nematic phase well beyond T_c has remained elusive. Here, we present angle-resolved magneto transport measurements on Sr_xBi₂Se₃ that disentangle anisotropic magnetoresistance (AMR), planar Hall effect (PHE), and a distinct twofold-symmetric component. This residual term exhibits fixed orientation along the crystallographic nematic axis and is invariant under different current-path, revealing its intrinsic origin. Remarkably, the signal persists up to 200 K, far exceeding the fluctuation regime. Our findings point to a high-temperature nematic phase in the normal state, likely driven by Pomeranchuk-type Fermi surface distortion. This establishes nematicity as a fundamental and robust electronic instability beyond the superconducting condensate.