Electronic Landscape of the Nodal-Line Semimetal Series LnSbTe

The lanthanide based antimony tellurides (LnSbTe, Ln = Pr, Tb, Er) represent a family of nonsymmorphic topological semimetals that host symmetry-protected nodal-line states arising from the interplay of crystal symmetry, spin-orbit coupling (SOC), magnetism and 4f electron correlations. In this work we present a systemactic study of the electronic band structure of the materials of this series utilizing DFT based theoretical calculations and angle-resolved photoemission spectroscopy (ARPES), affirming multiple Dirac crossings in the Γ-X and Γ-M high symmetry directions. The SOC-induced gap evolution, which increases systematically with heavier lanthanides, reveals the tunable role of relativistic effects in governing the band degeneracy. In PrSbTe and TbSbTe, the nodal crossings remain nearly gapless, while in ErSbTe a clear SOC-driven gap is resolved experimentally, consistent with theoretical predictions. Temperature dependent thermodynamic and electrical transport measuremnts exhibit multiple paramagnetic to antiferromagnetic transitions across different LnSbTe's. These results establish LnSbTe as an ideal model platform for exploring the transition from weak to strong SOC regimes within a single structural framework, and highlight the robustness of nonsymmorphic symmetry-protected electronic states.