Ultrafast optical spectroscopy of FeAs-based superconductors

The mechanism of iron -based superconductors, which is the second discovered family of high -temperature superconductors, is one of the most attractive research hotspots in modern physics. From the condensed matter perspective, the abundant ordered states in iron -based superconductors originate from the interaction between the microscopic degrees of freedom of electron, lattice, spin, and orbit. Recently, the rapid development of femtosecond lasers has resulted in the emergence of ultrafast optical spectroscopy as a powerful tool for understanding the microscopic mechanism of various interesting phenomena in materials and the interaction between degrees of freedom and has been widely applied in high -temperature superconductor research. Herein, the most recent results on the application of ultrafast optical spectroscopy for studying FeAs-based superconductors are presented, including the gap function, identification of various orders in the time domain, interpretation of the relation between the ordered states and superconductivity, and role of coherent phonons in forming Cooper pairs.