Strong pressure-dependent electron-phonon coupling in FeSe

We have computed the correlated electronic structure of FeSe and its dependence on the A(1g) mode versus compression. Using the self-consistent density functional theory-dynamical mean field theory (DFT-DMFT) with continuous time quantum Monte Carlo, we find that there is greatly enhanced coupling between some correlated electron states and theA(1g) lattice distortion. Superconductivity in FeSe shows a very strong sensitivity to pressure, with an increase in T-c of almost a factor of 5 within a few GPa, followed by a drop, despite monotonic pressure dependence of almost all electronic properties. We find that the maximum A(1g) deformation potential behaves similar to the experimental T-c. In contrast, the maximum deformation potential in DFT for this mode increases monotonically with increasing pressure.