Topological nodal line state in superconducting NaAlSi compound

Superconductors with a nontrivial band structure are promising to realize a topological superconducting state. Herein, we report the presence of a topological phase in a well-known superconductor, NaAlSi. Our first-principles computations show that NaAlSi naturally possesses four nodal lines in the k_z = 0 and k_z = π planes and hosts clear drumhead surface states. Comparing with those identified in other superconductors, the nodal line band structure of NaAlSi can more favor experimental detection on considering that: (1) it possesses four nodal lines in total in the system; (2) all the nodal lines appear slightly below the Fermi level; (3) the nodal lines do not coexist with other fermions or extraneous bands. Our findings indicate that NaAlSi is an excellent material platform to investigate the entanglement of superconducting and topological nodal line states.