Enhancement of electron-phonon coupling due to increased magnetism and applied hydrostatic pressure in FeSe

Abstract Inspired by the parabolic trend of the superconducting transition temperature(Tc) of bulk FeSe
under hydrostatic pressure, we investigated the effect of magnetism and hydrostatic pressure on the
electron-phonon coupling (EPC) in FeSe using density-functional perturbation theory. We found
that both magnetism and hydrostatic pressure enhanced EPC. The enhancement of the EPC is
mainly attributed to phonon softening and deformation potential induced by magnetism, rather
than Fermi surface nesting. Furthermore, we investigated the effect of spin 
fluctuations on superconductivity
by applying the random phase approximation method (RPA). A possible application of
our results to the phase diagram of FeSe under hydrostatic pressure was discussed, and we demonstrated
that when EPC and spin fluctuations are both considered, a parabolic superconducting Tc
may be obtained, providing a plausible explanation for the phase of FeSe under hydrostatic pressure.