Research on the interplay between nematicity and superconductivity in FeSe superconductors

As the structurally simplest iron-based superconductor, FeSe is a key material for understanding the relationship between electronic nematic order and superconducting order. However, under different experimental tuning conditions, these two ordered states exhibit complex and contradictory interactions described as competition, cooperation, or even decoupling. This review systematically consolidates experimental evidence related to these controversies and examines the potential spin or orbital origins of the nematic order. In conclusion, we present a new physical picture in which the superconducting order and the nematic order may be independently dominated by distinct electronic structures, namely the electron pockets and hole pockets. This provides a new perspective for achieving a unified understanding of the complex phase diagram of FeSe.