• Open Access

Topological Phases in the Single-Layer FeSe

Ningning Hao and Jiangping Hu
Phys. Rev. X 4, 031053 – Published 24 September 2014

Abstract

A distinct electronic structure was observed in the single-layer FeSe which shows surprisingly high-temperature superconductivity over 65 K. Here, we demonstrate that the electronic structure can be explained by the effective strain effect due to substrates. More importantly, we find that this electronic structure can be tuned into robust topological phases from a topologically trivial metallic phase by the spin-orbital interaction and couplings to substrates. The topological phase is robust against any perturbations that preserve the time-reversal symmetry. Our study suggests that nontrivial topology and high-Tc superconductivity can be intertwined in the single FeSe layer to search novel physics.

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  • Received 22 April 2014

DOI:https://doi.org/10.1103/PhysRevX.4.031053

This article is available under the terms of the Creative Commons Attribution 3.0 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

Authors & Affiliations

Ningning Hao1,2 and Jiangping Hu1,2,3,4

  • 1Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, China
  • 2Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA
  • 3Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
  • 4Collaborative Innovation Center of Quantum Matter, Beijing, China

Popular Summary

Topological insulators and high-temperature superconductors are some of the most fascinating materials in condensed-matter physics. Their combination of topological properties and superconductivity can lead to marvelous new physics, such as the creation of Majorana particles. Normally, combinations of properties are induced through a proximity effect by placing a topological insulator close to a conventional superconductor to induce superconductivity. Superconductors with high critical temperatures, however, are hardly candidates for such an integration process because they have extremely short coherent lengths in their superconducting state and are strongly incompatible with other materials. As a result, there has been little overlap between high-temperature superconductors and topological insulators. We determine that single-layer FeSe, a pure two-dimensional electron system, not only serves as the building block for iron-chalcogenide high-temperature superconductors, but it can also be a topological insulator.

Single-layer FeSe is epitaxially grown on SrTiO3; tensile strain on the film arises from the lattice mismatch between bulk FeSe and single-layer FeSe. Electron-doped FeSe displays superconductivity at temperatures over 65 K, the highest superconducting temperature known among iron-based superconductors. Without electron doping, the material is a semiconductor with a small energy gap. One of our key predictions is that when the spin-orbital coupling of FeSe overcomes the gap, the material becomes a topological insulator. Since the semiconductor gap in single-layer FeSe is only induced through coupling to a substrate, adjusting the substrate provides a controllable procedure to tune the single-layer FeSe into a topological material.

Our results build a bridge between the fields of high-temperature superconductivity and topology; we propose that magnetic transport measurements can be used to determine the topological phase of FeSe. New important physics and applications may emerge when nontrivial topology and high-temperature superconductivity can be combined within a single material.

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Vol. 4, Iss. 3 — July - September 2014

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