Combining topology and superconductivity provides a powerful tool for investigating fundamental physics as well as a route to fault-tolerant quantum computing. There is mounting evidence that the Fe-Based Superconductor FeTe0.55Se0.45 (FTS) may also be topologically non-trivial. Should the superconducting order be s±, then FTS could be a higher order topological superconductor with Helical Hinge Zero Modes (HHZM).To test the presence of these modes we developed a new method for making normal metal/superconductor junctions via 2D atomic crystal heterostructures. As expected,junctions in contact with the hinge reveal a sharp zero-bias anomaly whose suppression with temperature and magnetic field only along the c-axis are completely consistent with the presence of HHZM. This feature is completely absent when tunneling purely into the c-axis, and its characteristics are also inconsistent with other origins of zero bias anomalies. Furthermore, additional measurements with soft-point contacts in bulk samples with various Fe interstitial contents demonstrate the intrinsic nature of the observed mode. Thus we provide evidence that FTS is indeed a higher order topological superconductor as well as a new method for probing 2D atomic crystals.
@article{arxiv.1902.10723,
title = {Evidence for Helical Hinge Zero Modes in an Fe-Based Superconductor},
author = {Mason J. Gray and Josef Freudenstein and Shu Yang F. Zhao and Ryan OConnor and Samuel Jenkins and Narendra Kumar and Marcel Hoek and Abigail Kopec and Takashi Taniguchi and Kenji Watanabe and Ruidan Zhong and G. D. Gu and K. S. Burch},
journal= {arXiv preprint arXiv:1902.10723},
year = {2019}
}