Unusual change in the Dirac-cone energy band upon two-step magnetic transition in CeBi

TL;DR

This study uses ARPES to investigate how a two-step magnetic transition in CeBi affects its topological surface states, revealing a complex interaction between magnetism and band structure inversion.

Contribution

It provides the first detailed ARPES analysis of the evolution of Dirac-cone surface states across a two-step antiferromagnetic transition in CeBi.

Findings

Inverted band structure at the X point confirmed by soft-x-ray ARPES.

Double Dirac-cone appears in the first AF phase at 25 K.

Single Dirac-cone reappears below the second AF transition at 14 K.

Abstract

We have performed angle-resolved photoemission spectroscopy (ARPES) on CeBi which undergoes a two-step antiferromagnetic (AF) transition with temperature. Soft-x-ray ARPES has revealed the inverted band structure at the X point of bulk Brillouin zone for CeBi (and also for LaBi) as opposed to LaSb with non-inverted band structure. Low-energy ARPES on CeBi has revealed the Dirac-cone band at the Gamma point in the paramagnetic phase associated with the bulk band inversion. On the other hand, a double Dirac-cone band appears on entering the first AF phase at T = 25 K, whereas a single Dirac-cone band recovers below the second AF transition at T = 14 K. The present result suggests an intricate interplay between antiferromagnetism and topological surface states in CeBi.