Distinct Electronic Origins of Superconductivity and Nematicity in FeSe.

The complex interplay between superconductivity, nematicity, and magnetism in iron-based superconductors remains a significant challenge in understanding its high-temperature superconductivity. Despite that numerous experiments aim at revealing the underlying mechanisms for superconductivity and nematicity by varying multiple tuning parameters, the inherent entanglement of these parameters complicates the isolation of the fundamental factors that drive the transitions. Here, by introducing a novel hydrothermal treatment to FeSe, we are able to effectively reduce interstitial Fe without altering the crystal structure and magnetic properties. This treatment results in a notable increase in carrier density and mobility, simultaneously enhancing both superconducting and nematic transition temperatures. Combining our experimental results with previous investigations, we reveal distinct pocket-influenced mechanisms: superconducting order is primarily influenced by electron pockets, while nematic order is driven by hole pockets. The results demonstrate the independent mechanisms of superconductivity and nematicity in FeSe, offering new perspectives on high-temperature superconductivity.