Atomic line defects and topological superconductivity in unconventional superconductors

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 $s$-wave and $d$-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.

arXiv comment16 pages, 9 figures. To be published in Physical Review X

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• Vortex-line topology in iron-based superconductors with and without second-order topology
• Two-particle Berry phase mechanism for Dirac and Majorana Kramers pairs of corner modes
• Phase-manipulation-induced Majorana Mode and Braiding Realization in Iron-based Superconductor Fe(Te,Se)
• Origin of Topological Surface Superconductivity in FeSe${}_{0.45}$Te${}_{0.55}$
• Shot-noise and differential conductance as signatures of putative topological superconductivity in FeSe${}_{0.45}$Te${}_{0.55}$
• Kramers Fulde-Ferrell state and superconducting spin diode effect
• Anisotropic gap structure and sign reversal symmetry in monolayer Fe(Se,Te)
• In the Pursuit of Majorana Modes in Iron-based High-$T_c$ Superconductors
• Topological superconductivity driven by correlations and linear defects in multiband superconductors
• Magnetic anisotropy from linear defect structures in correlated electron systems
• Phase diagrams of superconducting topological surface states
• Symmetry-protected topological wire in a topological vacuum