Modulation of Dirac electrons in epitaxial Bi2Se3 ultrathin films on van-der-Waals ferromagnet Cr2Si2Te6

TL;DR

This study explores how the Dirac surface states in ultrathin Bi2Se3 films are affected by epitaxial growth on a ferromagnetic substrate, revealing the importance of interfacial coupling in topological insulator heterostructures.

Contribution

It demonstrates the modulation of Dirac electrons in Bi2Se3 films via epitaxial growth on a van-der-Waals ferromagnet, highlighting the role of interfacial coupling.

Findings

Gapless Dirac cone in 6QL Bi2Se3 on CST

Significant gap in 2QL Bi2Se3, larger than on Si(111)

No change in gap across ferromagnetic transition

Abstract

We investigated the Dirac-cone state and its modulation when an ultrathin film of topological insulator Bi2Se3 was epitaxially grown on a van-der-Waals ferromagnet Cr2Si2Te6 (CST) by angle-resolved photoemission spectroscopy. We observed a gapless Dirac-cone surface state in 6 quintuple-layer (QL) Bi2Se3 on CST, whereas the Dirac cone exhibits a gap of 0.37 eV in 2QL counterpart. Intriguingly, this gap is much larger than those for Bi2Se3 films on Si(111). We also revealed no discernible change in the gap magnitude across the ferromagnetic transition of CST, suggesting the very small characteristic length and energy scale of the magnetic proximity effect. The present results suggest a crucial role of interfacial coupling for modulating Dirac electrons in topological-insulator hybrids.