Interband scattering- and nematicity-induced quantum oscillation frequency in FeSe

Understanding the nematic phase observed in the iron-chalcogenide materials is crucial for describing their superconducting pairing. Experiments on FeSe_1-xSₓ showed that one of the slow Shubnikov-de Haas quantum oscillation frequencies disappears when tuning the material out of the nematic phase via chemical substitution or pressure, which has been interpreted as a Lifshitz transition [Coldea et al., npj Quantum Mater. 4, 2 (2019); Reiss et al., Nat. Phys. 16, 89 (2020)]. Here, we present a generic, alternative scenario for a nematicity-induced sharp quantum oscillation frequency, which disappears in the tetragonal phase and is not connected to an underlying Fermi surface pocket. We show that different microscopic interband scattering mechanisms---for example, orbital-selective scattering---in conjunction with nematic order can give rise to this quantum oscillation frequency beyond the standard Onsager relation. We discuss implications for iron-chalcogenides and the interpretation of quantum oscillations in other correlated materials.