Boundary-obstructed topological high-T${}_c$ superconductivity in iron pnictides

Abstract

Non-trivial 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 non-trivial band subject to intrinsic or external superconducting proximity effect. Here, we propose a new class of topological superconductors which 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 Ca${}_{1-x}$La${}_x$FeAs${}_2$, to be a highly suited material candidate for our proposal, which can be tested by edge spectroscopy. Because of the boundary-obstruction, the topologically non-trivial feature of the 112 pnictides does not reveal itself for a bulk-only torus band analysis without boundaries, and as such 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 evidence for extended s-wave order in the iron pnictides.

8 pages, 4 figures + supplementary materials

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• Hierarchy of higher-order topological superconductors in three dimensions
• Higher-order topological phases in crystalline and non-crystalline systems: a review
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• Boundary Topological Superconductors
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• Hybrid-order topological odd-parity superconductors via Floquet engineering
• Sublattice-sensitive Majorana Modes
• Generalization of Benalcazar-Bernevig-Hughes model to arbitrary dimensions
• High-temperature Majorana corner modes in a $d+i{d}^{\prime }$ superconductor heterostructure: Application to twisted bilayer cuprate superconductors
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• Meissner effect induced Majorana zero modes at small magnetic field
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• Proposal for realizing and probing topological crystalline insulators in optical lattices