Electron-Phonon Coupling at Topological Insulator Surfaces from Helium Atom Scattering Experiments

Electron-phonon coupling plays an important role for a variety of phenomena like
the modification of low-energy electronic excitations in metals by the coupling to
lattice vibrations, which may influence their transport and thermodynamic
properties. Helium atom scattering (HAS) has been shown to be a sensitive probe
of electron−phonon interaction properties at surfaces. Benedek and colleagues
developed a quantum-theoretical derivation that allows the determination of
electron-phonon coupling parameters λ for metals and metallic thin films from
experimentally measured temperature-dependent helium diffraction intensities and
phonon dispersion curves [1]. By adapting their theory to the case of topological
insulators, we were able to extract an averaged λ from the Debye-Waller
attenuation of the elastic diffraction peaks measured at surface temperatures
between 110 and 355 K [2]. Electron-phonon coupling parameters for the surfaces
of Bi2Se3, Bi2Te3, Bi2Te2Se, and Sb2Te3 were obtained this way. Moreover at the
Bi2Te2Se (111) surface, a charge density wave (CDW) was identified that is
stabilized by a coupling of Dirac topological electronic states to the crystal lattice
via electron-phonon interaction [3].