Ex Situ Fabrication of Superconducting Nanostructures for Low-Temperature STM

TL;DR

This paper presents a novel ex situ fabrication method for creating atomically clean, nanostructured topological insulator-superconductor heterostructures suitable for high-resolution STM/STS studies, advancing the exploration of topological superconductivity.

Contribution

It introduces a scalable ex situ lithographic patterning approach combined with in situ cleaving, enabling high-quality nanostructures for STM/STS without surface contamination.

Findings

Superconducting gaps observed in STM/STS measurements.

Pristine planar nanoribbons achieved within continuous TI films.

Proximity effect evidenced by suppressed gaps on nanoribbons.

Abstract

Nanofabrication of topological insulator (TI) devices is essential for accessing edge and interface states, but conventional lithography and etching compromise the atomically clean surfaces required for scanning tunneling microscopy and spectroscopy (STM/STS). We demonstrate a fabrication strategy that combines ex situ lithographic patterning with in situ ultrahigh-vacuum cleaving and flipping, yielding atomically clean, nanopatterned TI-superconductor heterostructures suitable for STM/STS. In Design I, nanoribbons were defined by etching trenches into a TI film and capping with Nb. This enabled spectroscopy on large areas, although edge quality was limited by etch debris. In Design II, local thinning defined buried nanoribbons within a continuous TI film, producing pristine planar surfaces. STM/STS revealed well-developed superconducting gaps in the surrounding film, with suppressed gaps on the nanoribbons, consistent with vertical proximity coupling. This approach establishes a reproducible pathway for high-resolution STM/STS studies of proximitized nanostructures, providing a scalable platform for exploring topological superconductivity.