Chemical potential dependent gap-opening at the Dirac surface states of Bi2Se3 induced by aggregated substitutional Cr atoms

TL;DR

This study reveals that aggregated substitutional Cr atoms induce a chemical potential dependent gap in the Dirac surface states of Bi2Se3, observable at room temperature, without requiring long-range ferromagnetic order.

Contribution

It demonstrates that Cr atom aggregation causes a chemical potential dependent gap in Bi2Se3 surface states, independent of ferromagnetic ordering, supported by spectroscopy and first principles calculations.

Findings

Gap opens at room temperature in Cr-doped Bi2Se3 surface states.

Gap size decreases with increasing electron doping.

Cr atoms form superparamagnetic multimers contributing to gap opening.

Abstract

With angle-resolved photoemission spectroscopy, gap-opening is resolved at up to room temperature in the Dirac surface states of molecular beam epitaxy grown Cr-doped Bi2Se3 topological insulator films, which however show no long-range ferromagnetic order down to 1.5 K. The gap size is found decreasing with increasing electron doping level. Scanning tunneling microscopy and first principles calculations demonstrate that substitutional Cr atoms aggregate into superparamagnetic multimers in Bi2Se3 matrix, which contribute to the observed chemical potential dependent gap-opening in the Dirac surface states without long-range ferromagnetic order.