  Interaction 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. In this study, we report
the formation of polarons at the alkali dosed MoSe2 surface, where Rashba-like
spin splitting of the conduction band states is caused by an inversion-symmetry
breaking electric field. In addition, we observe the crossover from phonon-like
to plasmon-like polaronic spectral features at MoSe2 surface with increasing
doping. Our findings support the concept of electron-phonon coupling 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.
