Fingerprints of inelastic transport at the surface of the topological insulator Bi 2 Se 3: Role of electron-phonon coupling

We report on electric-field and temperature-dependent transport measurements in exfoliated thin crystals of the Bi2Se3 topological insulator. At low temperatures (<50 K) and when the chemical potential lies inside the bulk gap, the crystal resistivity is strongly temperature dependent, reflecting inelastic scattering due to the thermal activation of optical phonons. A linear increase of the current with voltage is obtained up to a threshold value at which current saturation takes place. We show that the activated behavior, the voltage threshold, and the saturation current can all be quantitatively explained by considering a single optical-phonon mode with energy â Ω≈8 meV. This phonon mode strongly interacts with the surface states of the material and represents the dominant source of scattering at the surface at high electric fields. © 2014 American Physical Society.