Dirac fermions in condensed matter provide a versatile platform for exploring novel electronic phenomena and fundamental physics principles. Following the discovery of graphene, it was observed that certain layered materials can host planar square nets of atoms within their lattice, featuring a two-atom basis and supporting large-bandwidth Dirac bands. To date, several families of square net materials have been identified, exhibiting Dirac semimetal or nodal-line phases that host a diverse range of electronic and magnetic quantum properties. Here, we introduce a new class of square net semimetals: the binary rare-earth diantimonide compounds. Using angle-resolved photoemission spectroscopy and density functional theory calculations on the series precursor, ${\mathrm{LaSb}}_2$, we investigate the relationship between crystal structure and electronic topology. Our results reveal that the distinctive staggered symmetry of the square net layers induces a split double nodal-line structure in the low-energy dispersion. Furthermore, we predict that this splitting of the bands is accompanied by a Rashba-2 effect, establishing the rare-earth diantimonides as a compelling platform for studying Dirac spin-transport phenomena.

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• Electrical properties
• Spin-phonon coupling
• Spintronics
• Nodal-line semimetals
• Topological materials
• Angle-resolved photoemission spectroscopy
• Density functional theory