Anomalous dressing of Dirac fermions in the topological surface state of Bi₂Se₃, Bi₂Te₃, and Cu-doped Bi₂Se₃

Takeshi Kondo, Y. Nakashima, Y. Ota, Y. Ishida, W. Malaeb, K. Okazaki, S. Shin, M. Kriener, Satoshi Sasaki, Kouji Segawa, and Yoichi Ando

Accepted Monday Apr 29, 2013

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 ~ 3 and ~ 15-20 meV associated with an exceptionally large coupling constant l of ~ 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 ~ 3 meV mode coupling is found to be enhanced in the superconducting state of CuxBi2Se3.