Electronic band structure of a nodal line semimetal candidate ErSbTe

The $Ln\mathrm{SbTe}$ ($Ln=$ lanthanides) family is well known for hosting a plethora of intriguing characteristics stemming from its crystalline symmetry, magnetic structure, $4f$ electronic correlation, and spin-orbit coupling (SOC) phenomena. In this work, we investigate the nodal-line semimetal candidate ErSbTe through transport and thermodynamic measurements as well as angle-resolved photoemission spectroscopy (ARPES) complemented by first-principles calculations. Temperature-dependent susceptibility and resistivity measurements reveal a paramagnetic to antiferromagnetic transition at 1.94 K and a secondary anomaly at 1.75 K. The zero field resistivity measurement does not show the characteristic humplike feature, commonly observed in the other $Ln\mathrm{SbTe}$ materials. Our ARPES measurements show a diamond-shaped Fermi surface and symmetry-enforced crossings along the $\overline{\mathrm{\ensuremath{\Gamma}}}\text{\ensuremath{-}}\overline{\text{X}}$ direction as well as a momentum-dependent gap peaking along the $\overline{\mathrm{\ensuremath{\Gamma}}}\text{\ensuremath{-}}\overline{\text{M}}$ direction, consistent with our first principles calculations. This study demonstrates the critical role of SOC in shaping the electronic structure of ErSbTe.