Abstract
Topological superconductors (TSCs) are correlated quantum states with simultaneous off-diagonal long-range order and nontrivial topological invariants. They produce gapless or zero-energy boundary excitations, including Majorana zero modes and chiral Majorana edge states with topologically protected phase coherence essential for fault-tolerant quantum computing. Candidate TSCs are very rare in nature. Here, we propose a novel route toward emergent quasi-one-dimensional (1D) TSCs in naturally embedded quantum structures such as atomic line defects in unconventional spin-singlet -wave and -wave superconductors. We show that inversion symmetry breaking and charge transfer due to the missing atoms lead to the occupation of incipient impurity bands and mixed-parity spin-singlet and -triplet Cooper pairing of neighboring electrons traversing the line defect. Nontrivial topological invariants arise and occupy a large part of the parameter space, including the time-reversal symmetry-breaking Zeeman coupling due to applied magnetic field or defect-induced magnetism, creating TSCs in different topological classes with robust Majorana zero modes at both ends of the line defect. Beyond providing a novel mechanism for the recent discovery of zero-energy bound states at both ends of an atomic line defect in monolayer Fe(Te,Se) superconductors, the findings pave the way for new material realizations of the simplest and most robust 1D TSCs using embedded quantum structures in unconventional superconductors with large pairing energy gaps and high transition temperatures.
- Received 10 June 2020
- Revised 7 December 2020
- Accepted 12 January 2021
DOI:https://doi.org/10.1103/PhysRevX.11.011041
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)
Popular Summary
Topological superconductors (TSCs) are unusual materials that conduct electricity with zero resistance while also hosting quasiparticles that are their own antiparticle at the TSC’s boundary. Those quasiparticles—known as Majorana zero modes—may be essential to implementing certain types of robust quantum computation. However, candidates for TSCs are rare in nature. Here, we show that a quasi-1D TSC can emerge in certain 1D quantum structures, such as atomic line defects, embedded in unconventional superconductors with higher transition temperature.
The quantum structures, such as line defects, are formed by removing a chain of atoms in the bulk unconventional superconductor. Such a line defect breaks inversion symmetry, which induces spin-orbit coupling around it. We find that the spin-orbit interaction between the line defect and the bulk superconductor effectively generates a quasi-1D TSC along the line defect, which gives rise to a type of Majorana zero mode at both ends of the quantum structure.
Our work provides a possible explanation for the recent observation by scanning tunneling microscopy of robust Majorana zero modes at both ends of an atomic line defect in an iron-based superconductor. It further offers a path toward quantum structure engineering of quasi-1D TSCs with Majorana zero modes at the high operating temperatures of unconventional superconductors.
