Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 52: Superconductivity: Fe-based Superconductors – FeSe and others

TT 52.6: Talk

Wednesday, March 18, 2015, 10:45–11:00, H 2053

Correlation-driven topological Fermi surface transition in FeSe — I. Leonov¹, •S. L. Skornyakov^2,3, V. I. Anisimov^2,3, and D. Vollhardt¹ — ¹TP III, Center for Electronic Correlations and Magnetism, Univ. Augsburg, Germany — ²Institute of Metal Physics, Yekaterinburg, Russia — ³Ural Federal Univ., Yekaterinburg, Russia

We present results of a theoretical investigation of the electronic structure and phase stability of paramagnetic FeSe obtained within a combination of ab initio methods for calculating band structure and dynamical mean-field theory [1]. Our results reveal an entire reconstruction of the Fermi surface topology upon a moderate expansion of the lattice (Lifshitz transition), with a change of magnetic correlations from the in-plane magnetic wave vector (π,π) to (π,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. Our results predict a structural transition of FeSe upon a ca. 10% expansion of the lattice volume as well as a topological change of the Fermi surface of FeSe upon partial substitution Se by Te, which is accompanied with a sharp increase of the local moments. We expect that these changes are responsible for the experimentally observed increase of T_c in FeSe upon doping with Te. The microscopic origin for superconductivity in this system is then due to a Van Hove singularity close to the Fermi level. This identification may open a new route to increase T_c even further.

[1] I. Leonov, S. L. Skornyakov, V. I. Anisimov, D. Vollhardt,

arXiv:1411.0604 (2014).