Topological properties of non-centrosymmetric superconductors $T$Ir$_{2}$B$_{2}$ ($T$=Nb, Ta)

TL;DR

This paper predicts that NbIr2B2 and TaIr2B2 are topological Weyl metals with complex surface states, suggesting they could host three-dimensional topological superconductivity due to their intrinsic superconductivity and nontrivial bulk Fermi surfaces.

Contribution

First-principles calculations and symmetry analysis reveal the topological Weyl metal nature of NbIr2B2 and TaIr2B2, highlighting their potential for topological superconductivity.

Findings

NbIr2B2 has 12 Weyl points without SOC.

TaIr2B2 has 4 Weyl points without SOC.

Surface Fermi arcs are explicitly demonstrated.

Abstract

A recent experiment reported two new non-centrosymmetric superconductors NbIr$_{2}$B$_{2}$ and TaIr$_{2}$B$_{2}$ with respective superconducting transition temperatures of 7.2 K and 5.2 K and further suggested their superconductivity to be unconventional [K. G\'ornicka \textit{et al}., Adv. Funct. Mater. 2007960 (2020)]. Here, based on first-principles calculations and symmetry analysis, we propose that $T$Ir$_{2}$B$_{2}$ ($T$=Nb, Ta) are topological Weyl metals in the normal state. In the absence of spin-orbit coupling (SOC), we find that NbIr$_{2}$B$_{2}$ has 12 Weyl points, and TaIr$_{2}$B$_{2}$ has 4 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, NbIr$_{2}$B$_{2}$ and TaIr$_{2}$B$_{2}$ have 16 and 20 pairs of Weyl points, respectively. The surface Fermi arcs are explicitly demonstrated. On the (110) surface of TaIr$_{2}$B$_{2}$, we find extremely long surface Fermi arcs ($\sim$0.6 ${\text{\AA}}^{-1}$) 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, $T$Ir$_{2}$B$_{2}$ may thus provide a very promising platform to explore the three-dimensional topological superconductivity.