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  • Featured in Physics
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Nontrivial Boundary-Mediated Superconducting Transport in a TRSB Topological Iron-Based Superconductor

Wenyao Liu1,*, Gabriel Natale1,*, Camron Farhang2, Michael Geiwitz1, Qishuo Tan3, Xingyao Guo4, Mason Gray1, Vincent Lamberti1, Jazzmin Victorin1 et al.

Huairuo Zhang5,6, James L. Hart7, Vsevolod Belosevich1, Xi Ling3,8,9, Qiong Ma1, Wan Kyu Park10, Kenji Watanabe11, Takashi Taniguchi12, Judy J. Cha7, Albert V. Davydov5, Kin Chung Fong13,14,15, Ethan G. Arnault16, Genda Gu17, Rui-Xing Zhang18,19, Enrico Rossi20, Jing Xia2, and Kenneth S. Burch1,†

  • *These authors contributed equally to this work.
  • †Contact author: ks.burch@bc.edu
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Phys. Rev. X 16, 041022 – Published 22 October, 2026

DOI: https://doi.org/10.1103/8vgt-twh5

Abstract

The interplay of superconductivity, band topology, and spontaneous time-reversal-symmetry breaking (TRSB) is expected to enable topological superconducting boundary states. Intriguingly, the iron-chalcogenide superconductor FeTe0.55Se0.45 exhibits spontaneous magnetization in the superconducting state, motivating its use as a single-material platform in which three ingredients coexist. Here, we report evidence for a nontrivial, boundary-mediated superconducting transport response in exfoliated Fe(Te,Se) devices, exhibiting long-range nonlocality and strongly suppressed thermal broadening. Polar Kerr measurements establish that TRSB emerges below TKerr<Tc and coexists with superconductivity across multiple Fe(Te,Se) compositions studied here, providing an independent symmetry-breaking scale that can be directly compared with transport. To reliably access boundary transport, we engineer crystallographically sharp, continuous edges and implement side-surface-dominant contacts, as validated by contact-size analysis and cross-sectional imaging. Under these conditions, topological FeTe0.55Se0.45 exhibits an anomalous conductance plateau that is absent in topologically trivial FeTe0.40Se0.60 and Fe1.02Te0.55Se0.45 under comparable measurements. This plateau requires both the source and drain to be attached to uninterrupted sharp edges, persists over micrometer-scale separations far exceeding the bulk coherence length, has markedly reduced thermal decoherence, and collapses when the drain is moved to the top surface. Its temperature evolution is governed by TRSB: The plateau shows minimal thermal broadening below TKerr* and disappears near TKerr rather than Tc. Collectively, the doping selectivity, TRSB correlation, edge-geometry requirement, and long-range nonlocal nature establish experimentally grounded criteria for identifying boundary-mediated superconducting transport in FeTe0.55Se0.45 and motivate further phase-sensitive and theoretical work to determine its microscopic origin.

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Surprising Feature in a Topological Superconductor Candidate

Published 22 October, 2026

A new hint of topological superconductivity has been identified in an iron-based superconductor.

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Popular Summary

Identifying unambiguous boundary signatures of topological superconductivity remains a persistent challenge because conventional states can mask or mimic exotic boundary modes. We addressed this challenge by fabricating Fe(Te,Se) devices with crystallographically controlled edges to isolate the long-range, nonlocal transport expected from protected boundary modes.

We report evidence for edge-selective nonlocal superconducting transport in a single-material platform, without relying on an engineered heterostructure. We observe a distinct conductance plateau whose nonlocal response spans distances approaching 1000× the bulk superconducting coherence length and appears exclusively along sharp, continuous boundaries of the topological phase. It is absent in nontopological controls and along rough, stepped edges, while its temperature evolution follows spontaneous magnetic ordering rather than the bulk superconducting transition. These results distinguish the response from conventional contact artifacts and bulk-mediated processes and establish experimentally grounded criteria for identifying topological boundary transport. Our work provides a reliable framework for probing topological superconducting boundary modes and advancing their future implementation in fault-tolerant quantum technologies.

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Phys. Rev. X 16, 041022– Published 22 October, 2026
  • Received 19 March 2026
  • Accepted 25 August 2026
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