Absorption edge, urbach tail, and electron-phonon interactions in topological insulator Bi2Se3 and band insulator (Bi0.89In0.11)2Se3

We employ infrared transmission spectroscopy to explore the temperature-dependent absorption edge and electron-phonon (e-ph) interaction in topological insulator Bi2Se3 and band insulator (Bi0.89In0.11)2Se3 films. Upon heating from 5 K to 300 K, the absorption edge shifts from 262 to 249 meV for Bi2Se3 and from 367 to 343 meV for (Bi0.89In0.11)2Se3. By analyzing the temperature dependence of the Urbach tail, the significant role of Raman-active phonon mode E g 2 in e-ph interaction is identified, which agrees well with the ab initio calculation.