Impact of Se concentration and distribution on topological transition in FeTe1-xSex crystals

TL;DR

This study investigates how selenium concentration and distribution affect the electronic structure and topological transition in FeTe1-xSex superconductors, revealing key factors influencing Majorana states.

Contribution

It combines DFT and Hamiltonian analysis to systematically analyze the impact of Se concentration and distribution on topological properties, a novel approach in this context.

Findings

Maximum SOC gap at x=0.5

Se distribution modulates SOC gap and Majorana states

Critical role of pz-pz and dx2-y2-pz interactions in band inversion

Abstract

A topological transition in high-temperature superconductors FeTe1-xSex, occurring at a critical range of Se concentration x, underlies their intrinsic topological superconductivity and emergence of Majorana states within vortices. Nonetheless, the influence of Se concentration and distribution on the electronic states in FeTe1-xSex remains unclear, particularly concerning their relationship with the presence or absence of Majorana states. In this study, we combine density functional theory (DFT) calculations, pz-dxz/yz-based and Wannier-based Hamiltonian analysis to systematically explore the electronic structures of diverse FeTe1-xSex compositions. Our investigation reveals a nonlinear variation of the spin-orbit coupling (SOC) gap between pz and dxz/yz bands in response to x, with the maximum gap occurring at x = 0.5. The pz-pz and dx2-y2-pz interactions are found to be critical for pd band inversion. Furthermore, we ascertain that the distribution of Se significantly modulates the SOC gap, thereby influencing the presence or absence of Majorana states within local vortices.