  Three-component fermion beyond the conventional Dirac Weyl Majorana
classification attracts extensive attentions recently and many efforts have
been paid to explore their superconductivity. Based on first-principles
calculations, we systematically investigate the electron-phonon coupling (EPC)
in the three-component fermion materials WN, WC and TaN. The EPC in pristine
and pressured WC and TaN are to small to induce superconductivity. Electron
doping can efficiently enhance the EPC strength and the predicted Tcs reach the
value of experiments. Upon 0.6 electron/unitcell doping, the EPC strength of
TaN is boosted by two orders of magnitude and Tc can even be as high as 27 K,
revealing the crucial role of charge doping in the formation of
superconductivity observed in WC and TaN. In stark contrast, pristine WN
exhibits overwhelmingly strong EPC and can be a good superconductor with a high
transition temperature Tc of 31 K. The strong EPC in WN are dictated by a
synergistic effect of strong Fermi nesting and large deformation potential.
Going down from three-dimension (3D) to three-dimension (2D), WN thin film
(i.e. monolayer W3N4) is also an intrinsic superconductor with Tc of 11 K. Most
importantly, monolayer W3N4 host Dirac nodal lines protected by mirror symmetry
in the absence of spin-orbit coupling (SOC), Including SOC, the Dirac nodal
lines split into three pairs of spinful Weyl rings. These nodal lines lies
closely near the Fermi level, they are pure and clean without other nontrivial
bands, which is scarce in real materials and making the exotic topological
properties easily accessible in experiment. The coexistence of
superconductivity with high transition temperature and topological states in WN
and its 2D film provide a promising platform for exploring topological
superconductivity.
