Superconducting Dome in La 3 − x Sr x Ni 2 O 7 − δ Thin Films

The ambient-pressure superconductivity in La_{3}Ni_{2}O_{7} thin films via compressive epitaxial strain provides a highly accessible platform for diverse characterization techniques, facilitating the studies of high-temperature superconductivity. Here, we systematically map the phase diagram and reveal the superconducting dome with an electron-hole crossover in compressively strained La_{3-x}Sr_{x}Ni_{2}O_{7-δ} thin films by simultaneously tuning Sr doping and oxygen content. The maximum transition temperature (T_{c}) coincides with an anomalous sign change in the Hall coefficient (R_{H}), reminiscent of electron-doped cuprates, which may signal a Fermi surface reconstruction. Beyond the superconducting dome, a ln1/T insulating regime and a T-linear resistivity regime are also resolved, resembling behaviors observed in cuprates and infinite-layer nickelates. This work reveals a dome-shaped relationship between T_{c} and R_{H} and establishes a key framework for understanding unconventional superconductivity in nickelate systems.