Giant plateau in the THz Faraday angle in gated Bi2Se3

TL;DR

This study observes a remarkably flat plateau in the terahertz Faraday angle in gated Bi2Se3 thin films, indicating quantized Hall effects and dissipative channels, with implications for topological insulator surface states.

Contribution

It reports the first observation of a giant, stable Faraday angle plateau in Bi2Se3, revealing new insights into topological surface states under gating and magnetic fields.

Findings

Plateau in Faraday angle persists over a wide gate voltage range.

The plateau is significantly flatter than expected from a single Landau Level.

Dissipative conductivity channels are associated with the plateau.

Abstract

We report gated terahertz Faraday angle measurements on epitaxial Bi2Se3 thin films capped with In2Se3. A plateau is observed in the real part of the Faraday angle at an onset gate voltage corresponding to no band bending at the surface which persists into accumulation. The plateau is two orders of magnitude flatter than the step size expected from a single Landau Level in the low frequency limit, quantized in units of the fine structure constant. At 8 T, the plateau extends over a range of gate voltage that spans an electron density greater than 14 times the quantum flux density. Both the imaginary part of the Faraday angle and transmission measurements indicate dissipative off-axis and longitudinal conductivity channels associated with the plateau.