Effect of spin fluctuations on superconductivity in V and Nb: A first-principles study

We study the superconductivity in typical $d$-band elemental superconductors V and Nb with the recently developed nonempirical computational scheme based on the density functional theory for superconductors. The effect of ferromagnetic fluctuation (paramagnon) on the superconducting transition temperature ${T}_{\mathrm{c}}$, which, in principle, suppresses the $s$-wave superconducting pairing, is quantified without any empirical parameter. We show that the strong paramagnon effect cancels the ${T}_{\mathrm{c}}$-enhancing effects of the phonon-mediated pairing and dynamical screened Coulomb interaction.