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arXiv · 2412.07993

Topological Insulator nano-SQUID: Flux-tunable platform for topological superconductivity

Ella Nikodem·Jakob Schluck·Henry F. Legg·Max Geier·Michal Papaj·Mahasweta Bagchi·Liang Fu·Yoichi Ando
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Abstract

Many efforts have been made in the past decade to realize topological superconductivity using superconducting proximity effect, but an ideal platform is still lacking. A 3D topological insulator (TI) is promising for this purpose due to the spin-momentum-locked surface state. Here we propose a novel yet simple TI platform which gives rise to a topological phase that is robust against disorder. It consists of a bulk-insulating rectangular TI nanowire laterally sandwiched by two superconductors. In this structure, the top and bottom surfaces individually work as SNS line junctions, forming a nanometer-scale columnar SQUID in which the nanowire cross-section defines the threading magnetic flux $\Phi$ in axial magnetic fields. We theoretically show that, when the two junctions are asymmetric, a robust topological phase occurs periodically for a wide range of $\Phi$, independently of the chemical potential. Our experiment found that a TI device of this structure indeed behaves as a columnar nano-SQUID where the supercurrent flows only through the top and bottom surfaces with vanishing bulk contribution. Furthermore, the top/bottom asymmetry can be tuned by a back gate, a key ingredient for the topological phase.

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Ella Nikodem, Jakob Schluck, Henry F. Legg, Max Geier, Michal Papaj, Mahasweta Bagchi, Liang Fu, Yoichi Ando. 2024-12-11. Topological Insulator nano-SQUID: Flux-tunable platform for topological superconductivity. https://arxiv.org/abs/2412.07993

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