Fano q-reversal in topological insulator Bi2Se3

TL;DR

This study investigates the magneto-optical response of Bi2Se3, revealing strong electron-phonon coupling and the first observed magnetic field-driven Fano q-reversal, advancing understanding of topological insulator interactions.

Contribution

It reports the first observation of magnetic field-driven Fano q-reversal in a topological insulator, linking electron-phonon coupling with magnetic field effects.

Findings

Strong electron-phonon coupling evidenced by asymmetric phonon line-shape.

Fano asymmetry parameter q changes sign at cyclotron resonance degeneracy.

First demonstration of magnetic field-driven q-reversal in a topological insulator.

Abstract

We studied magneto-optical response of a canonical topological insulator Bi$_2$Se$_3$ with the goal of addressing a controversial issue of electron-phonon coupling. Magnetic-field induced modifications of reflectance are very pronounced in the infrared part of the spectrum, indicating strong electron-phonon coupling. This coupling causes an asymmetric line-shape of the 60 cm$^{-1}$ phonon mode, and is analyzed within the Fano formalism. The analysis reveals that the Fano asymmetry parameter (q) changes sign when the cyclotron resonance is degenerate with the phonon mode. To the best of our knowledge this is the first example of magnetic field driven q-reversal.