Evidence for Helical Hinge Zero Modes in an Fe-Based Superconductor

• Published in: Nano letters Vol. 19; no. 8; pp. 4890 - 4896
• Main Authors: Gray, Mason J, Freudenstein, Josef, Zhao, Shu Yang F, O’Connor, Ryan, Jenkins, Samuel, Kumar, Narendra, Hoek, Marcel, Kopec, Abigail, Huh, Soonsang, Taniguchi, Takashi, Watanabe, Kenji, Zhong, Ruidan, Kim, Changyoung, Gu, G. D, Burch, K. S
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.08.2019
• Subjects: 2D superconductor; Andreev reflection; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Higher order topology; hinge modes; Andreev reflection; 2D superconductor; hinge modes; Higher order topology
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.9b00844

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 nontrivial. Should the superconducting order be s±, then FTS could be a higher order topological superconductor with helical hinge zero modes (HHZMs). To test the presence of these modes, we have fabricated normal-metal/superconductor junctions on different surfaces via 2D atomic crystal heterostructures. As expected, junctions in contact with the hinge reveal a sharp zero bias anomaly that is absent when tunneling purely into the c-axis. Additionally, the shape and suppression with temperature are consistent with highly coherent modes along the hinge and are incongruous with other origins of zero bias anomalies. 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.