Robust gapless surface state and Rashba-splitting bands upon surface deposition of magnetic Cr on Bi$_2$Se$_3$

TL;DR

Surface deposition of Cr on Bi$_2$Se$_3$ preserves the gapless surface state and induces Rashba-splitting bands, contrasting with bulk doping, due to different impurity configurations affecting magnetic properties.

Contribution

This study reveals that surface Cr deposition does not open a gap in the topological surface state, emphasizing the role of impurity placement in magnetic topological insulators.

Findings

Cr deposition does not open a gap at the Dirac point

Surface Cr induces Rashba-splitting bands

Impurity site configuration influences magnetic properties

Abstract

The interaction between magnetic impurities and the gapless surface state is of critical importance for realizing novel quantum phenomena and new functionalities in topological insulators. By combining angle-resolved photoemission spectroscopic experiments with density functional theory calculations, we show that surface deposition of Cr atoms on Bi$_2$Se$_3$ does not lead to gap opening of the surface state at the Dirac point, indicating the absence of long-range out-of-plane ferromagnetism down to our measurement temperature of 15 K. This is in sharp contrast to bulk Cr doping, and the origin is attributed to different Cr occupation sites. These results highlight the importance of nanoscale configuration of doped magnetic impurities in determining the electronic and magnetic properties of topological insulators.