Topological insulator homojunctions including magnetic layers: the example of n-p type ($n$-QLs Bi$_2$Se$_3$/Mn-Bi$_2$Se$_3$) heterostructures

TL;DR

This study explores how magnetic layers influence topological insulator properties in Bi$_2$Se$_3$ homojunctions, revealing the evolution of surface states and band bending effects through molecular beam epitaxy and surface spectroscopy.

Contribution

It demonstrates the controlled development of topological surface states in Bi$_2$Se$_3$/Mn-Bi$_2$Se$_3$ heterostructures, highlighting the role of magnetic doping and interface effects.

Findings

Topological surface states reappear around 9 QL layers.

Mn-induced gap at Dirac point fills in an hourglass pattern.

Band bending effects can be independently tailored.

Abstract

Homojunctions between Bi$_2$Se$_3$ and its Mn-doped phase are investigated as a sample geometry to study the influence of spin degrees of freedom on topological insulator properties. $n$ quintuple layers (QLs) of Bi$_2$Se$_3$ are grown ontop of Mn-doped Bi$_2$Se$_3$ by molecular beam epitaxy for $0\le n \le 30\,$QLs, allowing to unhamperedly monitor the development of electronic and topological properties by surface sensitive techniques like angle resolved photoemission spectroscopy. With increasing $n$, a Mn-induced gap at the Dirac point is gradually filled in an "hourglass" fashion to reestablish a topological surface state at $n \sim 9\,$QLs. Our results suggest a competition of upwards and downwards band bending effects due to the presence of an n-p type interface, which can be used to tailor topological and quantum well states independently.