Quasiparticle interference on the surface of 3D topological insulator Bi$_{2}$Se$_{3}$ induced by cobalt adatom in the absence of ferromagnetic ordering

TL;DR

This study investigates how cobalt adatoms affect quasiparticle interference on Bi$_{2}$Se$_{3}$ surfaces, revealing anisotropic standing waves without magnetic order, and attributes the anisotropy to warped surface states with out-of-plane spin components.

Contribution

It provides detailed experimental analysis of cobalt adatom scattering effects on topological insulator surfaces, highlighting the role of surface state warping and spin orientation.

Findings

Cobalt atoms adsorb on Se sites and act as strong scatterers.

No long-range magnetic order is observed, and the Dirac cone remains gapless.

Anisotropic standing waves are due to warped iso-energy contours and out-of-plane spin.

Abstract

Quasiparticle interference induced by cobalt adatoms on the surface of the topological insulator Bi$_{2}$Se$_{3}$ is studied by scanning tunneling microscopy, angle-resolved photoemission spectroscopy and X-ray magnetic circular dichroism. It is found that Co atoms are selectively adsorbed on top of Se sites and act as strong scatterers at the surface, generating anisotropic standing waves. A long-range magnetic order is found to be absent, and the surface state Dirac cone remains gapless. The anisotropy of the standing wave is ascribed to the heavily warped iso-energy contour of unoccupied states, where the scattering is allowed due to a non-zero out-of-plane spin.