Experimental observation of dual magnetic states in topological insulators

Wenqing Liu; Yongbing Xu; Liang He; Gerrit van der Laan; Rong Zhang; Kang Wang

doi:10.1126/sciadv.aav2088

Experimental observation of dual magnetic states in topological insulators

Sci Adv. 2019 Feb 8;5(2):eaav2088. doi: 10.1126/sciadv.aav2088. eCollection 2019 Feb.

Authors

Wenqing Liu^{1

2}, Yongbing Xu^{1

3}, Liang He^{1

4}, Gerrit van der Laan⁵, Rong Zhang², Kang Wang⁴

Affiliations

¹ York-Nanjing Joint Center (YNJC) for Spintronics and Nanoengineering, School of Electronics Science and Engineering, Nanjing University, Nanjing 210093, China.
² Department of Electronic Engineering, Royal Holloway University of London, Egham TW20 0EX, UK.
³ Department of Electronic Engineering, The University of York, York YO10 5DD, UK.
⁴ Department of Electrical and Computer Engineering, Department of Materials Science and Engineering, and Department of Physics, University of California, Los Angeles, Los Angeles, CA 90095, USA.
⁵ Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE, UK.

Abstract

The recently discovered topological phase offers new possibilities for spintronics and condensed matter. Even insulating material exhibits conductivity at the edges of certain systems, giving rise to an anomalous quantum Hall effect and other coherent spin transport phenomena, in which heat dissipation is minimized, with potential uses for next-generation energy-efficient electronics. While the metallic surface states of topological insulators (TIs) have been extensively studied, direct comparison of the surface and bulk magnetic properties of TIs has been little explored. We report unambiguous evidence for distinctly enhanced surface magnetism in a prototype magnetic TI, Cr-doped Bi₂Se₃. Using synchrotron-based x-ray techniques, we demonstrate a "three-step transition" model, with a temperature window of ~15 K, where the TI surface is magnetically ordered while the bulk is not. Understanding the dual magnetization process has strong implications for defining a physical model of magnetic TIs and lays the foundation for applications to information technology.