Transport anomalies and lattice effects in superconducting Nb-doped Bi[Formula: see text]Se[Formula: see text]

The interplay between symmetry-breaking orders in topological materials dictates their exotic quantum states. Here, we report a combined transport, NMR, and electron diffraction study of Nb-doped Bi[Formula: see text]Se[Formula: see text], with doping level x ([Formula: see text]). Electron diffraction reveals superlattice features and periodic lattice distortions, accompanied by a pronounced resistivity anomaly between 150 and 200 K and NMR line broadening below this temperature, consistent with a temperature-driven lattice and electronic instability. The resistivity anomaly scales with nominal Nb concentration x and coexists with superconductivity at low temperatures. While its microscopic origin remains unresolved, our observations reveal competing possibilities, including charge ordering, structural disorder, and frozen lattice distortions, highlighting the rich interplay between structure and electronic states in this system. Our results position Nb[Formula: see text]Bi[Formula: see text]Se[Formula: see text] as a tunable platform for investigating intertwined electronic and structural phenomena in topological materials.