Dirac lines and loop at the Fermi level in the time-reversal symmetry breaking superconductor LaNiGa2

• DOI: 10.1038/s42005-021-00771-5
• Publication Date: 2022-01-13T11:03:33Z
• Authors: Jackson R. Badger; Yundi Quan; Matthew C. Staab; Shuntaro Sumita; Antonio Rossi; Kasey P. Devlin; Kelly Neubauer; Daniel S. Shulman; James C. Fettinger; Peter Klavins; Susan M. Kauzlarich; Dai Aoki; Inna M. Vishik; Warren E. Pickett; Valentin Taufour
• Keywords: T-symmetry

Unconventional superconductors have Cooper pairs with lower symmetries than in conventional superconductors. In most unconventional superconductors, the additional symmetry breaking occurs relation to typical ingredients such as strongly correlated Fermi liquid phases, magnetic fluctuations, or strong spin-orbit coupling noncentrosymmetric structures. this article, we show that time-reversal superconductor LaNiGa$_2$ is enabled by its previously unknown topological electronic band structure. Our single crystal diffraction experiments indicate a nonsymmorphic structure, contrast reported symmorphic The transform $k_z=\pi/c$ plane of Brillouin zone boundary into node-surface. Band-structure calculations reveal distinct surfaces become degenerate on node-surface and form Dirac lines loop at level. Two related points remain under coupling. ARPES measurements confirm provide evidence for surface degeneracies These unique features enable an superconducting gap which can be broken absence other ingredients. therefore crystalline breaks without any overlapping ordering fluctuations. findings will future discoveries