Two-Band Nodal Line Structure with Robust Surface States in the Cubic NaPdCl Compound.

Recent advancements in topological states have expanded from insulators to semimetals and metals, characterized by band crossings near the Fermi level. In this study, we use first-principles calculations and crystal symmetry analysis to uncover a complex nodal structure in cubic compound NaPdCl. This structure, formed by only two bands, features six intersecting butterfly-like nodal lines on the (110) surface, protected by mirror symmetry . The associated surface states span the entire Brillouin zone, enhancing the experimental observability. Remarkably, this nodal line configuration remains robust under both Hubbard correction and spin-orbit coupling effects, highlighting NaPdCl as a promising material for both research and applications. To further provide a practical reference, the stabilities of NaPdCl have been verified from different perspectives and several important mechanical parameters have been derived. The well-defined band structure, simple topological configuration, and robust surface state render NaPdCl a compelling candidate for both theoretical exploration and experimental validation, suggesting significant potential for further research and potential applications.