Raman Study of Cooper Pairing Instabilities in (Li_{1 − x}Fe_x)OHFeSe

Pairing in unconventional superconductors is one of the most important open questions in physics and materials science. Although superconductivity occurs along with magnetism in all systems having high transition temperatures (T_c) there exist various relevant proposals other than spin physics. Thus, an Fe-based material without the nesting paradigm of a central hole pocket and electron pockets encircling the X (Y) points is of crucial importance for clarifying the pairing mechanism. Here, we studied the electronic Raman spectra of (Li_1-xFe_x)OHFeSe as a function of light polarization and temperature. In the B_1g spectra two well resolved peaks appear below T_c, which originate from collective excitations. Given the experimental band structure of (Li_1-xFe_x)OHFeSe, our results favor pairing between the hybridized electron bands. Our work demonstrates the proximity of pairing states and the importance of band structure effects in the Fe-based compounds.