• Open Access

Boundary-Obstructed Topological High-Tc Superconductivity in Iron Pnictides

Xianxin Wu, Wladimir A. Benalcazar, Yinxiang Li, Ronny Thomale, Chao-Xing Liu, and Jiangping Hu
Phys. Rev. X 10, 041014 – Published 20 October 2020
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Abstract

Nontrivial topology and unconventional pairing are two central guiding principles in the contemporary search for and analysis of superconducting materials and heterostructure compounds. Previously, a topological superconductor has been predominantly conceived to result from a topologically nontrivial band subject to an intrinsic or external superconducting proximity effect. Here, we propose a new class of topological superconductors that are uniquely induced by unconventional pairing. They exhibit a boundary-obstructed higher-order topological character and, depending on their dimensionality, feature unprecedently robust Majorana bound states or hinge modes protected by chiral symmetry. We predict the 112 family of iron pnictides, such as Ca1xLaxFeAs2, to be highly suited material candidates for our proposal, which can be tested by edge spectroscopy. Because of the boundary obstruction, the topologically nontrivial feature of the 112 pnictides does not reveal itself for a bulk-only torus band analysis without boundaries, and as such, it had evaded previous investigations. Our proposal not only opens a new arena for highly stable Majorana modes in high-temperature superconductors but also provides the smoking gun for extended s-wave order in the iron pnictides.

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  • Received 9 April 2020
  • Revised 16 July 2020
  • Accepted 24 August 2020

DOI:https://doi.org/10.1103/PhysRevX.10.041014

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Xianxin Wu1,2,*, Wladimir A. Benalcazar1, Yinxiang Li3, Ronny Thomale4, Chao-Xing Liu1,†, and Jiangping Hu2,5,‡

  • 1Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
  • 2Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
  • 3Tin Ka-Ping College of Science, University of Shanghai for Science and Technology, Shanghai, 200093, China
  • 4Institut für Theoretische Physik und Astrophysik, Julius-Maximilians-Universität Würzburg, 97074 Würzburg, Germany
  • 5CAS Center of Excellence in Topological Quantum Computation and Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China

  • *xianxinwu@gmail.com
  • cxl56@psu.edu
  • jphu@iphy.ac.cn

Popular Summary

Studies of topological phases of matter—whose intrinsic properties are impervious to external change—and high-temperature superconductivity have had almost no overlap until very recently. The discovery of intrinsic topological properties in iron-based superconductors has brought these two fields together and provided a high-temperature platform for exploring topological superconductivity, an attractive property for quantum computation. However, no one has yet incorporated the unconventional pairing of electrons found in these superconductors. Here, we propose a new class of topological superconductors that are induced by this unconventional pairing.

Our newly proposed class of topological superconductors, based on an unconventional pairing, can possess Majorana modes—highly sought-after electron-hole superpositions, whose behavior could be exploited for quantum computation—and can be driven by the sign-change nature of the extended s-wave pairing in iron pnictides. Our theory also clarifies the boundary-obstructed nature of the topological property for this superconducting phase, whose topological nature is revealed only when boundaries are open. We predict the 112 family of iron pnictides, which contains an intrinsic topological insulator–high-temperature superconductor heterostructure, to be a natural material candidate for our proposal.

Our work significantly advances the understanding of topological superconductors and offers a promising high-temperature platform for Majorana modes. Most importantly, our work also provides a novel way to unambiguously identify the extended s-wave order in the iron pnictides, setting up a strong connection between topological phases of matter and unconventional superconductivity fields.

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Vol. 10, Iss. 4 — October - December 2020

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