Effect of uniaxial strain on the electronic structure of bulk NbReSi

Elemental rhenium (Re) was shown to exhibit time-reversal symmetry breaking in the superconducting (SC) state from a muon spin resonance experiment. Existence of nodes in the SC gap function, and its pairing nature remain elusive. Yet, this observation stimulated a search for time-reversal symmetry breaking and/or SC gap function with nodes in Re-rich compounds. Intriguingly, for some Re-included systems, time-reversal symmetry breaking has been observed in the SC state with isotropic gap functions. Recently, two crystalline forms of NbReSi such as hexagonal and orthorhombic structures in the SC state have been experimentally studied. For hexagonal NbReSi, the experimental data corroborates an upper critical field beyond the Pauli limit and multi-band SC gaps. Here we investigate, within first-principles methods, dominant orbitals and density of states at the Fermi level for the two forms of NbReSi with and without uniaxial strain, in order to have insights into the SC gap functions and their sensitivity to strain. We employ two first-principles methods including spin-orbit coupling such as solving Kohn-Sham equations and multiple scattering Green's function methods. We discuss the anisotropic nature of the band structure and compare with the experiments.