Fractional AC Josephson effect in a topological insulator proximitized by a self-formed superconductor

Abstract

A lateral Josephson junction in which the surface of a 3D topological insulator serves as the weak link should support topologically protected excitations related to Majorana fermions. The resulting $4\pi$-periodic current-phase relationship could be detected under high-frequency excitation by the suppression of odd Shapiro steps. Here, we demonstrate such devices through the self-formation of a Pd-Te superconducting layer from a telluride topological insulator, and observe suppressed first and third Shapiro steps. Other devices, including those where the Pd-Te layer is bolstered by an additional Al layer, show no suppression of Shapiro steps, a difference supported by simulations. Though we rule out the known trivial causes of suppressed Shapiro steps in our devices, we nevertheless argue that corroborating measurements and disorder-aware theoretical descriptions of these systems are needed before confidently claiming the observation of Majorana states.

arXiv comment10 pages, 5 figures, plus Supplemental Material

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Cited by in corpus (8)

• A quantum dot in germanium proximitized by a superconductor
• Low-damage electron beam lithography for nanostructures on Bi${}_2$Te${}_3$-class topological insulator thin films
• Missing odd-order Shapiro steps do not uniquely indicate fractional Josephson effect
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• Ubiquitous missing first Shapiro step in Al-InSb nanosheet Josephson junctions
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• Gate-Tunable Ambipolar Josephson Current in a Topological Insulator
• Planar Hall supercurrent and δϕ-shift in the topological Josephson junction