arXiv subjects

Colin Howard

Publications and source records attributed to Colin Howard.

4 recordsLinked to original sources

arXiv2013

Connecting electron and phonon spectroscopy data to consistently determine quasiparticle-phonon coupling on the surface of topological insulators

Photoemission and phonon spectroscopies have yielded widely varying estimates of the electron-phonon coupling constant λ on the surfaces of topological insulators, even for a particular material and technique. We connect the results of these experiments by determining the Dirac fermion quasiparticle spectral function using information from measured spectra of a strongly-interacting, low-lying optical surface phonon band. The manifest spectral features resulting from the coupling are found to vary on energy scales < 1 meV, and are distinct from those traditionally observed in the case of acoustic phonons in metals. We explore different means of determining λ from the electron perspective and identify definitions that yield values consistent with phonon spectroscopy.

cond-mat.mes-hall↗

arXiv2013

Electron-Phonon Coupling on the Surface of Topological Insulators

Topological insulators (TIs) are materials that have a bulk electronic band gap like an ordinary insulator but have protected conducting states on their surface. One of the most interesting properties of TIs is their spin helicity, whereby the spin is locked normal to the wave vector of the surface electronic state. The topological surface states should be very stable in TIs, since these spin-textured surface states are robust against spin-independent backscattering. Scattering from defects and other lattice imperfections is possible provided the spin is not completely flipped. However, the quality of TI crystals can be controlled by careful growth, whereas phonons will exist in even the most perfect crystals. Consequently, electron-phonon coupling (EPC) should be the dominant scattering mechanism for surface electronic states at finite temperatures. Hence, the study of EPC in TIs is of exceptional importance in assessing any potential applications. In this article both experimental and theoretical studies of the EPC on the surface of TIs are reviewed, with the contents mainly focused on the typical strong three dimensional TIs, such as Bi2Se3 and Bi2Te3.

cond-mat.mes-hall↗

arXiv2013

Anomalous behavior in the phonon dispersion of the (001) surface of Bi$_2$Te$_3$ determined from helium atom-surface scattering measurements

We employ inelastic helium atom-surface scattering to measure the low energy phonon dispersion along high-symmetry directions on the surface of the topological insulator Bi$_2$Te$_3$. Results indicate that one particular low-frequency branch experiences noticeable mode softening attributable to the interaction between Dirac fermion quasiparticles and phonons on the surface. This mode softening constitutes a renormalization of the real part of the phonon self-energy. We obtain the imaginary part, and hence lifetime information, via a Hilbert transform. In doing so we are able to calculate an average branch specific electron-phonon coupling constant $<λ_ν> = 1.44$.

cond-mat.mtrl-sci↗

arXiv2012

Electron-phonon Coupling on the Surface of the Topological Insulator Bi2Se3: Determined from Surface Phonon Dispersion Measurements

In this letter we report measurements of the coupling between Dirac fermion quasiparticles (DFQs) and phonons on the (001) surface of the strong topological insulator Bi2Se3. While most contemporary investigations of this coupling have involved examining the temperature dependence of the DFQ self-energy via angle-resolved photoemission spectroscopy (ARPES) measurements, we employ inelastic helium atom scattering to explore, for the first time, this coupling from the phonon perspective. Using a Hilbert transform, we are able to obtain the imaginary part of the phonon self-energy associated with a dispersive surface phonon branch identified in our previous work [1] as having strong interactions with the DFQs. From this imaginary part of the self-energy we obtain a branch-specific electron-phonon coupling constant of 0.43, which is stronger than the values reported form the ARPES measurements.

cond-mat.mtrl-sci↗