Orbital Selective Mott Transition and Topological Superconductivity of FeSe_1-xTe_x

The iron-based superconductor, FeSe_1-xTe_x (FST), obtained significant attention due to two emergent phenomena. The first is the topological superconductivity (TPSC) hosts Majorana Fermion in its boundary as a candidate of the topologically protected qubit [1,2]. The second is the orbital selective Mott transition (OSMT), a selective localization of the Fe(d_xy) orbital while other orbitals remain as itinerant [3]. This talk shows that the TPSC and the OSMT in the FST material are intimately connected [4]. We use the state-of-the-art linearized quasiparticle self-consistent GW plus dynamical mean-field theory framework with included spin-orbit coupling, which enables the quantitative description of the topological Dirac surface state of the FST material. We show that the topologically non-trivial band experiences a localization from the OSMT due to its Fe(d_xy) orbital origin. From this, we demonstrate that the TPSC could be realized for a regime that is not too far but not too close to the OSMT. This observation enables understanding and manipulation of the TPSC of iron-based superconductors. Also, this observation can explain the experimentally observed time-reversal symmetry breaking at the surface state of the FST material [5].

[1] G. Xu et al., Phys. Rev. Lett. 117, 047001 (2016),

[2] P. Zhang et al., Science 360, 182 (2018)

[3] M. Yi et al., Nat. Comm. 6, 1 (2015)

[4] Minjae Kim et al., https://arxiv.org/abs/2304.05002 (2023)

[5] C. Farhang et al., Phys. Rev. Lett. 130, 046702 (2023)