Anomalous dressing of Dirac fermions in the topological surface state of Bi2Se3, Bi2Te3, and CuxBi2Se3

TL;DR

This study investigates quasiparticle interactions on the topological surface states of Bi2Se3, Bi2Te3, and CuxBi2Se3, revealing strong mode couplings and their enhancement in the superconducting state, with implications for understanding surface excitations.

Contribution

It provides the first detailed measurement of strong mode couplings in topological surface states, highlighting the role of spin-plasmon excitations and their enhancement in superconductivity.

Findings

Strong mode couplings at ~3 and 15-20 meV energies.

Coupling constant of ~3, one of the strongest reported.

Enhanced mode coupling observed in the superconducting CuxBi2Se3.

Abstract

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, which leads to an exceptionally large coupling constant 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.