Magnetic interactions of 4$f$ electrons in the topological insulator chalcogenide Bi$_{2}$Se$_{3}$

TL;DR

This study investigates the magnetic interactions of 4f electrons in Bi2Se3 topological insulators with Gd doping, revealing unique magnetic behaviors and potential pathways for axion insulator research.

Contribution

It provides a microscopic analysis of Gd3+ spin dynamics in Bi2Se3, highlighting distinct 4f electron magnetism and its implications for topological properties.

Findings

Gd3+ spin dynamics show no significant Fermi surface change with doping

Unusual evolution of ESR spectra linked to Gd-impurity interactions

Potential local weak anti-localization effects around Gd3+ ions

Abstract

The gap opening mechanism of a topological insulator, the quantum anomalous Hall effect and the axion physics are still pressing open questions and a microscopic viewpoint to further understand the role of magnetism in topology is highly desirable. In this work we have performed a microscopic investigation, by means of electron spin resonance (ESR) along with complementary bulk measurements, on the chalcogenide (Bi$_{1-x}$Gd$_{x}$)$_{2}$Se$_{3}$ ($x$ = 0, 0.001, 0.002 and 0.006). Our analysis of the Gd$^{3+}$ spin dynamics reveal no significant change of the Fermi surface as a function of Gd$^{3+}$ concentration, which indicates that the 4$f$ magnetism is different from the non-local effects induced by transition metals ($d$ electrons) substitutions. Additionally, we observe an unusual evolution of the Gd$^{3+}$ ESR spectra as a function of the applied magnetic field, which we discuss considering the magnetic interaction between Gd$^{3+}$ 4$f$ electrons and impurity centers such as Se vacancies. This interaction would give rise to a local weak antilocalization effect surrounding the Gd$^{3+}$ ions. Such mechanism is observable due to particular details of the Gd$^{3+}$ 4$f$ electrons magnetism in this system compared to $d$ electrons. Our work points out that rare earth substitutions in this model topological insulator is a promising path to explore the axion insulating systems.