Polarons, Rashba spin splitting and Ising superconductivity in electron doped MoSe2

Coupling between electrons and phonons in solids is a key effect defining physical properties of materials such as electrical and thermal conductivity. In transitional metal dichalcogenides (TMDCs) the electron-phonon coupling results in the creation of polarons, quasiparticles that manifest themselves as discrete features in the electronic spectral function. Holstein polarons, driven by the multi-valley electron-phonon scattering, have been observed on an alkali-dosed MoS2 surface, however the experimentally measured spectral function did not display any spin-split features. In this study, we report the formation of polarons at the alkali-dosed MoSe2 surface, where Rashba-like spin splitting of the valence band states is caused by a strong inversion-symmetry breaking electric field. In addition, we observed the crossover from phonon to plasmon-like polaronic spectral features at MoSe2 surface with increased amount of dosed alkali metal atoms. Our findings support the concept of polaron mediated superconductivity in electron-doped layered TMDC materials, observed using ionic liquid gating technology. Furthermore, the discovered spin-splitting at the Fermi level could offer crucial experimental validation for theoretical models of Ising-type superconductivity in these materials.