Screening properties and plasmons of Hg(Cd)Te quantum wells

TL;DR

This paper investigates the polarization and plasmonic properties of Hg(Cd)Te quantum wells modeled by the BHZ framework, revealing two types of plasmons with potential for experimental detection.

Contribution

It provides a detailed analysis of the polarization function and plasmon modes in the BHZ model, bridging Dirac and Schrödinger physics in quantum wells.

Findings

Identification of two distinct plasmon types related to intra- and interband excitations

Analysis of screening properties across different parameter regimes

Predictions of observable plasmon signatures in experiments

Abstract

Under certain conditions, Hg(Cd)Te quantum wells (QWs) are known to realize a time-reversal symmetric, two-dimensional topological insulator phase. Its low-energy excitations are well-described by the phenomenological Bernevig-Hughes-Zhang (BHZ) model that interpolates between Schr\"odinger and Dirac fermion physics. We study the polarization function of this model in random phase approximation (RPA) in the intrinsic limit and at finite doping. While the polarization properties in RPA of Dirac and Schr\"odinger particles are two comprehensively studied problems, our analysis of the BHZ model bridges the gap between these two limits, shedding light on systems with intermediate properties. We gain insight into the screening properties of the system and on its characteristic plasma oscillations. Interestingly, we discover two different kinds of plasmons that are related to the presence of intra- and interband excitations. Observable signatures of these plasmons are carefully analyzed in a variety of distinct parameter regimes, including the experimentally relevant ones for Hg(Cd)Te QWs. We conclude that the discovered plasmons are observable by Raman or electron loss spectroscopy.