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 $d_{xz}/d_{yz}$ bands at the $M$ point across the Fermi level. We propose that superconductivity is strongly influenced, or even induced, by a van Hove singularity.

Figure 1

Total energy (upper panel) and mean fluctuating local moment (lower panel) of paramagnetic FeSe calculated for different temperatures by $\mathrm{GGA}+\mathrm{DMFT}$ as a function of the lattice constant.

Figure 2

Left panels: Spectral functions of paramagnetic FeSe obtained within non-spin-polarized GGA (shaded areas) and $\mathrm{GGA}+\mathrm{DMFT}$ (straight lines). Right panels: Orbitally resolved imaginary parts of the self-energies as computed by $\mathrm{GGA}+\mathrm{DMFT}$. The upper row corresponds to the lattice constant $a=7.1\mathrm{a}.\mathrm{u}.$, while the lower graphs display results for $a=7.35\mathrm{a}.\mathrm{u}.$

Figure 3

Fermi surface reconstruction in the ($k_x,k_y$) plane at $k_z=0$, calculated for paramagnetic FeSe using non-spin-polarized GGA (left panels) and $\mathrm{GGA}+\mathrm{DMFT}$ (right panels) for the lattice constants, $a=7.1\mathrm{a}.\mathrm{u}.$ (upper row) and $a=7.35\mathrm{a}.\mathrm{u}.$ (bottom row).

Figure 4

The $\mathbf{k}$-resolved spectral function of paramagnetic FeSe computed within non-spin-polarized GGA (left panels) and $\mathrm{GGA}+\mathrm{DMFT}$ (right panels) along the path $\mathrm{\Gamma }-X-M-\mathrm{\Gamma }$ for the lattice constants, $a=7.1\mathrm{a}.\mathrm{u}.$ (upper row) and $a=7.35\mathrm{a}.\mathrm{u}.$ (bottom row).