Anomalous Dressing of Dirac Fermions in the Topological Surface State of Bi2Se3, Bi2Te3, and Cu-Doped Bi2Se3

Quasiparticle dynamics on the topological surface state of Bi2Se3, Bi2Te3, and superconducting CuxBi2Se3 are studied by 7 eV laser-based angle resolved photoemission spectroscopy. We find strong mode couplings in the Dirac-cone surface states at energies of similar to 3 and similar to 15-20 meV associated with an exceptionally large coupling constant lambda of similar to 3, which is one of the strongest ever reported for any material. This result is compatible with the recent observation of a strong Kohn anomaly in the surface phonon dispersion of Bi2Se3, but it appears that the theoretically proposed spin-plasmon excitations realized in helical metals are also playing an important role. Intriguingly, the similar to 3 meV mode coupling is found to be enhanced in the superconducting state of CuxBi2Se3.