Non-magnetic ground state of Ni adatoms on Te-terminated bismuth chalcogenide topological insulators

TL;DR

This study demonstrates that Ni adatoms on Te-terminated bismuth chalcogenide topological insulators are non-magnetic due to a local Stoner criterion, contrasting with magnetic Fe adatoms, providing a platform to explore time-reversal symmetry effects.

Contribution

It reveals the non-magnetic ground state of Ni adatoms on topological insulators and relates this to local electronic structure and Stoner criterion, contrasting with magnetic Fe adatoms.

Findings

Ni adatoms show no magnetic moments due to Stoner criterion

Fe adatoms form large magnetic moments with out-of-plane anisotropy

Fermi level remains in the bulk band gap after adatom deposition

Abstract

We report on the quenching of single Ni adatom moments on Te-terminated Bi2Te2Se and Bi2Te3 topological insulator surfaces. The effect becomes manifested as a missing X-ray magnetic circular dichroism for resonant L3,2 transitions into partially filled Ni 3d states of occupancy n_d = 9.2. On the basis of a comparative study of Ni and Fe using scanning tunneling microscopy and ab initio calculations we are able to relate the element specific moment formation to a local Stoner criterion. While Fe adatoms form large spin moments of m_s = 2.54 mu_B with out-of-plane anisotropy due to a sufficiently large density of states at the Fermi energy, Ni remains well below an effective Stoner threshold for local moment formation. With the Fermi level remaining in the bulk band gap after adatom deposition, non-magnetic Ni and preferentially out-of-plane oriented magnetic Fe with similar structural properties on Bi2Te2Se surfaces constitute a perfect platform to study off-on effects of time-reversal symmetry breaking on topological surface states.