Correlation-driven topological Fermi surface transition in FeSe

The electronic structure and phase stability of paramagnetic FeSe is computed by using a combination of ab initio methods for calculating band structure and dynamical mean-field theory. Our results reveal a topological change (Lifshitz transition) of the Fermi surface upon a moderate expansion of the lattice. The Lifshitz transition is accompanied with a sharp increase of the local moments and results in an entire reconstruction of magnetic correlations from the in-plane magnetic wave vector $(\pi ,\pi )$ to $(\pi ,0)$. We attribute this behavior to a correlation-induced shift of the Van Hove singularity originating from the $d_{xy}$ and $d_{xz}\mathrm{/}{d}_{yz}$ bands at the M-point across the Fermi level. We propose that superconductivity is strongly influenced, or even induced, by a Van Hove singularity.