Spin-charge separation of plasmonic excitations in thin topological insulators

TL;DR

This paper explores the unique spin-charge separation in plasmonic excitations of thin topological insulators, emphasizing the importance of charge response in interpreting experimental data.

Contribution

It introduces a theoretical framework for understanding optical and acoustic plasmons in topological insulator slabs, including a formula to fit experimental observations.

Findings

Identification of charge and spin collective oscillations in thin topological insulators.

Explanation of experimental plasmon data by including depletion layer charge response.

Analytic formula for fitting plasmonic excitation data.

Abstract

We discuss plasmonic excitations in a thin slab of a topological insulators. In the limit of no hybridization of the surface states and same electronic density of the two layers, the electrostatic coupling between the top and bottom layers leads to optical and acoustic plasmons which are purely charge and spin collective oscillations. We then argue that a recent experiment on the plasmonic excitations of Bi2Se3 [Di Pietro et al, Nat. Nanotechnol. 8, 556 (2013)] must be explained by including the charge response of the two-dimensional electron gas of the depletion layer underneath the two surfaces. We also present an analytic formula to fit their data.