Dirac cone engineering in Bi$_2$Se$_3$ thin films

TL;DR

This paper demonstrates how to engineer ideal, isolated Dirac cones in Bi$_2$Se$_3$ thin films through surface atom substitutions, thickness control, and magnetic doping, enhancing their potential for spintronics applications.

Contribution

It introduces a method to realize an ideal Dirac cone in Bi$_2$Se$_3$ thin films by surface atom substitution and explores effects of thickness and magnetic doping.

Findings

Isolated Dirac cone achieved via surface Se atom substitution.

Thickness and magnetic doping influence Dirac cone properties.

Potential applications in spintronics devices.

Abstract

Topological insulators are distinguished from normal insulators by their bulk insulating gap and odd number of surface states connecting the inverted conduction and valence bands and showing Dirac cones at the time-reversal invariant points in the Brillouin zone. Bi-based three-dimensional strong topological insulator materials, Bi$_2$Se$_3$ and Bi$_2$Te$_2$, are known as high temperature topological insulators for their relatively large bulk gap and have one simple Dirac cone at the $\Gamma$ point. In spite of their clear surface state Dirac cone features, the Dirac point known as a Kramers point and the topological transport regime is located below the bulk valence band maximum. As a result of a non-isolated Dirac point, the topological transport regime can not be acquired and there possibly exist scattering channels between surface and bulk states as well. In this article we show that an ideal and isolated Dirac cone is realized in a slab geometry made of Bi$_2$Se$_3$ with appropriate substitutions of surface Se atoms. In addition to Dirac cone engineering by surface atom substitutions, we also investigate Bi$_2$Se$_3$ thin films in terms of thickness and magnetic substitutions, which can be linked to applications of spintronics devices.