Topological Surface State on a Fe-based High Tc Superconductor

Laser-based ARPES is used to examine FeTe_0.5Se_0.5. We observe the presence of a Dirac cone with helical spin structure as expected for a topological surface state and as previously reported¹. These experimental studies are compared with theoretical studies that take account of the disordered local magnetic effects related to the paramagnetism observed in this system. Including magnetic contributions in the theoretical description of the normal state is necessary to bring the chemical potential of the calculated electronic band structure into alignment with the experimental observations. Our studies performed above the superconducting transition temperature show evidence for a gap around the Dirac point reflecting mass acquisition associated with the breaking of time reversal symmetry. This points to the possibility of some form of surface magnetic order.

[1] P. Zhang et al., arXiv:1706.05163 (2017)