[Paper Review] Oxygen vacancy-induced anomalous Hall effect in a non-magnetic oxide

Athby H. Al‐Tawhid, Jesse Kanter+5 more|arXiv (Cornell University)|Sep 16, 2021

Electronic and Structural Properties of Oxides37 references4 citations

TL;DR

This study demonstrates the emergence of the anomalous Hall effect (AHE) in nominally non-magnetic KTaO3 due to oxygen vacancies, which induce local magnetic moments that scatter conduction electrons asymmetrically. The AHE transitions from extrinsic to intrinsic character and is governed by Berry curvature at low temperatures (T < 5 K), revealing a many-body mechanism for AHE in non-magnetic oxides.

ABSTRACT

The anomalous Hall effect, a hallmark of broken time-reversal symmetry and spin-orbit coupling, is frequently observed in magnetically polarized systems. Its realization in non-magnetic systems, however, remains elusive. Here, we report on the observation of anomalous Hall effect in nominally non-magnetic KTaO3. Anomalous Hall effect emerges in reduced KTaO3 and shows an extrinsic to intrinsic crossover. A paramagnetic behavior is observed in reduced samples using first principles calculations and quantitative magnetometry. The observed anomalous Hall effect follows the oxygen vacancy-induced magnetization response, suggesting that the localized magnetic moments of the oxygen vacancies scatter conduction electrons asymmetrically and give rise to anomalous Hall effect. The anomalous Hall conductivity becomes insensitive to scattering rate in the low temperature limit (T<5 K), implying that the Berry curvature of the electrons on the Fermi surface controls the anomalous Hall effect. Our observations describe a detailed picture of many-body interactions, triggering anomalous Hall effect in a non-magnetic system.

Motivation & Objective

• To investigate the origin of anomalous Hall effect (AHE) in non-magnetic oxides where AHE is typically absent.
• To determine whether oxygen vacancies in KTaO3 can induce magnetism and trigger AHE without long-range magnetic order.
• To clarify the interplay between defect-induced magnetism, electron scattering, and topological effects in non-magnetic oxides.
• To establish the role of Berry curvature in governing the AHE in the low-temperature regime.

Proposed method

• First-principles calculations were used to model the electronic structure and magnetic response of oxygen-vacancy-doped KTaO3.
• Quantitative magnetometry was employed to confirm paramagnetic behavior in reduced KTaO3 samples.
• Transport measurements were conducted to extract anomalous Hall conductivity and analyze its temperature and scattering rate dependence.
• The anomalous Hall conductivity was analyzed in the context of extrinsic (impurity scattering) and intrinsic (Berry curvature) mechanisms.
• The low-temperature behavior (T < 5 K) was examined to isolate the contribution of Berry curvature to the AHE.
• The interplay between oxygen vacancies, localized magnetic moments, and electron scattering was modeled to explain asymmetric scattering.

Experimental results

Research questions

• RQ1 Can the anomalous Hall effect emerge in a non-magnetic oxide like KTaO3 without long-range magnetic order?
• RQ2 What is the role of oxygen vacancies in inducing magnetism and enabling the anomalous Hall effect in KTaO3?
• RQ3 Is the anomalous Hall effect in reduced KTaO3 dominated by extrinsic scattering or intrinsic Berry curvature effects?
• RQ4 How does the anomalous Hall conductivity behave at low temperatures, and what does this imply about the underlying mechanism?
• RQ5 To what extent do many-body interactions involving oxygen vacancies and conduction electrons govern the anomalous Hall response?

Key findings

• The anomalous Hall effect is observed in reduced KTaO3, a nominally non-magnetic perovskite oxide, due to oxygen vacancies.
• Oxygen vacancies induce localized magnetic moments that scatter conduction electrons asymmetrically, giving rise to the anomalous Hall effect.
• The anomalous Hall effect exhibits a crossover from extrinsic to intrinsic character with decreasing temperature.
• At low temperatures (T < 5 K), the anomalous Hall conductivity becomes insensitive to scattering rate, indicating control by Berry curvature on the Fermi surface.
• First-principles calculations and magnetometry confirm a paramagnetic response in reduced KTaO3, supporting the absence of long-range magnetic order.
• The results reveal a many-body mechanism involving defect-induced magnetism and topological electron transport in a non-magnetic oxide system.