Helical edge and surface states in HgTe quantum wells and bulk insulators

TL;DR

This paper demonstrates the existence of helical edge states in HgTe quantum wells and surface states in bulk HgTe, establishing their topological insulator properties through realistic models and predicting experimental signatures.

Contribution

It provides a detailed theoretical analysis of helical edge and surface states in HgTe structures using realistic tight-binding models, confirming their topological insulator nature.

Findings

Helical edge states exist in HgTe quantum wells.

Bulk HgTe exhibits topological insulator behavior under strain.

Surface states are described by massless Dirac fermions.

Abstract

The quantum spin Hall (QSH) effect is the property of a new state of matter which preserves time-reversal, has an energy gap in the bulk, but has topologically robust gapless states at the edge. Recently, it has been shown that HgTe quantum wells realize this novel effect. In this work, we start from realistic tight-binding models and demonstrate the existence of the helical edge states in HgTe quantum wells and calculate their physical properties. We also show that 3d HgTe is a topological insulator under uniaxial strain, and show that the surface states are described by single-component massless relativistic Dirac fermions in 2+1 dimensions. Experimental predictions are made based on the quantitative results obtained from realistic calculations.