Unusual surface states associated with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="script">PT</mml:mi></mml:math>-symmetry breaking and antiferromagnetic band folding in NdSb

Abstract

We have performed angle-resolved photoemission spectroscopy on NdSb, which exhibits the type-I antiferromagnetism below ${T}_{\mathrm{N}}=16\phantom{\rule{4pt}{0ex}}\mathrm{K}$. By utilizing microfocused photons, we succeeded in selectively observing the band structure for all three types of $\text{single-}q$ antiferromagnetic (AF) domains at the surface. We found that two of the three surfaces whose AF-ordering vector lies within the surface plane commonly show twofold-symmetric surface states (SSs) around the bulk-band edges, whereas the other surface with an out-of-plane AF-ordering vector displays fourfold-symmetric shallow electronlike SS at the Brillouin-zone center. We suggest that these SSs commonly originate from the combination of the $\mathcal{PT}$- (space-inversion and time-reversal) symmetry breaking at the surface and the band folding due to the AF order. The present results pave a pathway toward understanding the relationship between the symmetry and the surface electronic states in antiferromagnets.