Rare-earth-doped Bi₂X₃ (X = Se, Te) as candidates for magnetic topological insulators

ABSTRACT

Electronic structures of rare-earth (R)-doped ${\mathrm{B}\mathrm{i}}_{2-x}{R}_x{X}_3$ ($R=\mathrm{C}\mathrm{e},\mathrm{G}\mathrm{d}$; $X=\mathrm{S}\mathrm{e},\mathrm{T}\mathrm{e}$) single crystals, which are promising candidates for magnetic topological insulators, have been investigated by employing soft X-ray absorption spectroscopy (XAS), soft X-ray magnetic circular dichroism (XMCD), and circular dichroism (CD) angle-resolved photoemission spectroscopy (ARPES). R $M_{4,5}$ XAS and XMCD measurements provide evidence that R ions are trivalent and magnetic, confirming that doped R ions have purely magnetic effects. ARPES measurements of ${\mathrm{B}\mathrm{i}}_{2-x}{\mathrm{C}\mathrm{e}}_x{\mathrm{S}\mathrm{e}}_3$ show a finite energy gap for x>0, arising from the broken time-reversal symmetry due to magnetic R impurities. CD-ARPES measurements of ${\mathrm{B}\mathrm{i}}_{2-x}{\mathrm{C}\mathrm{e}}_x{\mathrm{S}\mathrm{e}}_3$ reveal finite CD effects in the topological surface states. This work demonstrates that ${\mathrm{B}\mathrm{i}}_{2-x}{R}_x{X}_3$ ($R=\mathrm{C}\mathrm{e},\mathrm{G}\mathrm{d}$) are magnetic topological insulators.

KEYWORDS:

• Magnetic topological insulator
• ARPES
• XMCD
• XAS
• circular dichroism
• electronic structure

Acknowledgments

J.-S. Kang congratulates the 80th birthday of Prof. M. Brian Maple, and appreciates very much his prominent contribution to the research on the strongly-correlated electron systems.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

J.-S. Kang http://orcid.org/0000-0002-3012-7673

Additional information

Funding

This work was supported by the National Research Foundation of Korea (NRF) (No. 2019R1A2C1004929; 2017R1A2B3007918), and in part by the Research Fund 2019 of the Catholic University of Korea. Experiment at PLS was supported by Ministry of Science, ICT and Future Planning (MSIP) and Pohang Accelerator Laboratory (PAL) in Korea.