Robust topological state against magnetic impurities observed in superconductor PbTaSe2

TL;DR

This study demonstrates that the topological surface state in PbTaSe2 remains stable against dilute magnetic impurities, supporting its potential as a robust platform for topological quantum states.

Contribution

The paper provides experimental evidence of the robustness of PbTaSe2's topological surface state against magnetic impurities using STM and QPI analysis.

Findings

Topological surface state remains stable with up to 3% Fe coverage.

Fe adatoms exhibit large magnetic moments and sit at interstitial sites.

QPI patterns at the Fermi energy are robust against magnetic impurity perturbation.

Abstract

Magnetic impurities deposited on topological superconductor candidate PbTaSe2 can introduce a non-splitting zero-energy state inside the superconducting gap, which has been proposed as a field-free platform for topological zero modes. However, it is still unclear how robust the topological state in PbTaSe2 is against magnetic impurities, which is related to the topological nature of the zero-energy state as well as its potential for quantum computation. In this work, we use scanning tunneling microscopy (STM) to study the topological surface state in the normal state of PbTaSe2 under the perturbation of magnetic impurities. We visualize the quasi-particle interference (QPI) arising from the topological surface state. We then deposit Fe impurities on the surface to form atomic Fe adatoms. We find that each Fe adatom sits at a unique interstitial position on the surface and features a local state at high energies, both of which are consistent with our first-principles calculation that further reveals its large magnetic moment. Our systematic Fe deposition and subsequent measurements show that the arc-like QPI pattern at the Fermi energy is robust with up to 3% Fe coverage where the atomic nature of Fe adatoms still holds. Our results provide evidence that the topological surface state at the Fermi energy in PbTaSe2 is robust against dilute magnetic impurities.