The analysis of relationships among resistivity, temperature, and doping in the electron-doped cuprate ${\mathrm{La}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4+\delta }$ (LCCO) has yielded profound insights into its low-temperature transport behavior. Within the intermediate-temperature range of 70–200 K, a ubiquitous $T^2$ resistivity behavior emerges, distinct from the linear resistivity characteristic of the strange metal state below 50 K. Despite its prominence, the origin of the $T^2$ resistivity at various doping levels remains elusive, prompting debates on the sufficiency of Fermi-liquid theory. Here, a systematic electrical transport on epitaxial composition-spread films reveals a doping-independent intermediate-temperature region of $T^2$ behavior in the phase diagram of overdoped LCCO. This observation suggests a topologically stable Fermi surface with strong electron-phonon coupling. The Fermi liquid of polaronic quasiparticles and their interactions provides a plausible framework to understand the intermediate-temperature $T^2$ behavior in cuprate superconductors.

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• Superconductivity
• High-temperature superconductors
• Resistivity measurements