Electron–phonon interaction in NbB2: a comparison with MgB2

We present a comparison of electron–phonon interaction in NbB2 and MgB2, calculated using full-potential, density-functional-based methods in P6/mmm crystal structure. Our results, described in terms of (i) electronic structure, (ii) phonon density of states F(ω), (iii) Eliashberg function α2F(ω), and (iv) the solutions of the isotropic Eliashberg gap equation, clearly show significant differences in the electron–phonon interaction in NbB2 and MgB2. We find that the average electron–phonon coupling constant λ is equal to 0.59 for MgB2 and 0.43 for NbB2, leading to superconducting transition temperatures Tc at around 22 K for MgB2 and 3 K for NbB2.