Creation of Helical Dirac Fermions by Interfacing Two Gapped Systems of Ordinary Fermions

TL;DR

This paper demonstrates a novel method to create helical Dirac fermions by interfacing two gapped topological insulator films, confirmed through theoretical calculations and experiments, involving interface charge transfer and Rashba effect.

Contribution

The study introduces a new approach to generate helical Dirac fermions via interface engineering of gapped TI films, combining density functional theory and experimental validation.

Findings

Helical Dirac fermions can be created by interfacing two gapped TI films.

The Dirac fermions mainly originate from Bi bilayer states.

Interfacial charge transfer induces a giant Rashba effect.

Abstract

Topological insulators (TIs) are a unique class of materials characterized by a surface (edge) Dirac cone state of helical Dirac fermions in the middle of bulk (surface) gap. When the thickness (width) of TIs is reduced, however, interaction between the surface (edge) states will open a gap removing the Dirac cone. Using density function theory calculation, we demonstrate the creation of helical Dirac fermions from interfacing two gapped TI films, a single bilayer Bi grown on a single quintuple layer Bi2Se3 or Bi2Te3. The theoretical prediction is directly confirmed by experiment. We further show that the extrinsic helical Dirac fermions consists of predominantly Bi bilayer states, which are created by a giant Rashba effect due to interfacial charge transfer. Our findings provide a promising new method to create novel TI materials by interface engineering.