Measuring and Translating Electron Quasiparticle-phonon Interactions on the Surface of the Topological Insulator Bi2Te3

Speaker: Colin Howard

When: November 20, 2014 (Thu), 09:00AM to 10:00AM (add to my calendar)
Location: SCI 352

This event is part of the Departmental Seminars.

Dissertation Committee: Michael El-Batanouny, Claudio Chamon, Robert Carey, Karl Ludwig, William Skocpol

ABSTRACT: The topological insulators Bi2Se3 and Bi2Te3 have been the subjects of intense research over the past five years, even showing potential for use in emerging technologies. An important requirement for topological insulators in device-oriented applications, such as topological quantum information and low power spintronics devices, is the availability of dissipationless surface states in the topological transport regime. This requirement means an isolated Dirac cone fully separated from bulk bands, a Fermi level located at the Dirac point, and suppressed electron-phonon interactions. Because of the electron quasiparticles’ robustness against impurity scattering, electron-phonon scattering should be the dominant scattering mechanism for electron quasiparticles on these surfaces at finite temperatures. In this talk I will present a combined experimental, computational, and theoretical study of the electron quasiparticle-phonon interaction on the surface of Bi2Te3. I will start by describing how the measurements of the surface phonon dispersion are performed using helium atom surface scattering spectroscopy and will present the results. I will then move on to show how one can obtain the mode-specific electron phonon coupling parameter using a theoretical model derived within the random phase approximation. Integrating out the wavevector dependence allows us to define an average electron-phonon parameter that can be compared with results from electron spectroscopies. Finally, I will demonstrate a translation process, devised by our group and based upon a finite temperature Matsubara Green function formalism, which allows one to take information obtained experimentally from the phonon perspective to examine the coupling signatures from the electron perspective. This novel translation approach sheds light on problems associated with traditional methods of extracting the coupling parameter using electron spectroscopies and sets the requisite energy resolution to study the electron-phonon coupling in topological insulators.

Colin