Topological properties of noncentrosymmetric superconductors TIr2B2 (T=Nb, Ta)

A recent experiment reported two new noncentrosymmetric superconductors NbIr2B2 and TaIr2B2 with respective superconducting transition temperatures of 7.2 and 5.2 K and further suggested their superconductivity to be unconventional [K. Gornicka et al., Adv. Funct. Mater. 31, 2007960 (2021)]. Here, based on first-principles calculations and symmetry analysis, we propose that TIr2B2 (T = Nb, Ta) are topological Weyl metals in the normal state. In the absence of spin-orbit coupling (SOC), we find that NbIr2B2 has 12 Weyl points, and TaIr2B2 has four Weyl points, i.e., the minimum number under time-reversal symmetry; meanwhile, both of them have a nodal net composed of three nodal lines. In the presence of SOC, a nodal loop on the mirror plane evolves into two hourglass Weyl rings, along with the Weyl points, which are dictated by the nonsymmorphic glide mirror symmetry. Besides the rings, NbIr2B2 and TaIr2B2 have 16 and 20 pairs ofWeyl points, respectively. The surface Fermi arcs are explicitly demonstrated. On the (110) surface of TaIr2B2, we find extremely long surface Fermi arcs (similar to 0.6 angstrom(-1)) located 1.4 meV below the Fermi level, which should be readily probed in experiment. Combined with the intrinsic superconductivity and the nontrivial bulk Fermi surfaces, TIr2B2 may, thus, provide a very promising platform to explore the three-dimensional topological superconductivity.

Automated summary

Two new noncentrosymmetric superconductors, NbIr2B2 and TaIr2B2, were found to be topological Weyl metals in the normal state, with unique nodal structures. With the presence of spin-orbit coupling, they exhibit distinctive Weyl ring structures in addition to Weyl points. These characteristics make them a promising platform to explore three-dimensional topological superconductivity.