Twin Domain Structure in Magnetically Doped Topological Insulators

TL;DR

This study investigates how twin domain structures in magnetically doped topological insulators like Bi2Se3 influence their properties, defect interactions, magnetic behavior, and surface electronic structure using ab initio calculations.

Contribution

It provides new insights into the interaction between twin domains and magnetic defects, revealing how doping affects twin formation and surface states in topological insulators.

Findings

Twin planes repel each other over 3-4 nm distance.

Magnetic Mn and Fe defects favor close twin plane placement.

Twin planes suppress formation energy in the presence of magnetic dopants.

Abstract

Twin domains are naturally present in the topological insulator \BiSe{} and affect strongly its properties. While studies of its behavior for ideal \BiSe{} structure exist, little is known about their possible interaction with other defects. Extra information are needed especially for the case of artificial perturbation of topological insulator states by magnetic doping, which has attracted a lot of attention recently. Employing ab initio calculations based on layered Green's function formalism, we study the interaction between twin planes in \BiSe{}. We show the influence of various magnetic and non-magnetic chemical defects on the twin plane formation energy and discuss the related modification of their distribution. Furthermore, we examine the change of dopants' magnetic properties at sites in the vicinity of a twin plane, and the dopants' preference to occupy such sites. Our results suggest that twin planes repel each other at least over distance of $3-4$~nm. However, in the presence of magnetic Mn and Fe defects a close TP placement is preferred. Furthermore, calculated twin plane formation energies indicate that in this situation their formation becomes suppressed. Finally, we discuss the influence of twin planes on the surface band gap.