On the interplay of paramagnetism and topology in the Fe-based High Tc Superconductors

TL;DR

This study investigates the topological surface states in Fe-based high Tc superconductors, revealing the importance of magnetic effects for understanding their electronic structure through combined experimental and theoretical analysis.

Contribution

It demonstrates that incorporating magnetic contributions is essential for accurately modeling the electronic structure of FeTeSe superconductors with topological surface states.

Findings

Surface states with linear dispersion observed in FeTeSe compounds.

Circular polarization confirms helical spin structure of surface states.

Magnetic effects are crucial for aligning theoretical models with experimental data.

Abstract

The high Tc superconductor FeTe0.55Se0.45 has recently been shown to support a surface state with topological character. Here we use low-energy laser-based ARPES with variable light polarization, including both linear and circular polarization, to re-examine the same material and the related FeTe0.7Se0.3, with larger Te concentration. In both cases we observe the presence of a surface state displaying linear dispersion in a cone-like configuration. The use of circular polarization confirms the presence of helical spin structure. These experimental studies are compared with theoretical studies that account for the local magnetic effects related to the paramagnetism observed in this system in the normal state. In contrast to previous studies we find that including the magnetic contributions is necessary to bring the chemical potential of the calculated electronic band structure naturally into alignment with the experimental observations.