Proximity-induced superconductivity in (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ topological-insulator nanowires

TL;DR

This paper demonstrates the fabrication of superconducting topological insulator nanowires using (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$, enabling a tunable platform for exploring Majorana zero modes through proximity-induced superconductivity.

Contribution

It reports the first realization of robust proximity-induced superconductivity in BST nanowires with high interface transparency and suitable geometry for gate control.

Findings

Superconductivity successfully induced in BST nanowires.

Epitaxial and highly transparent interfaces achieved.

Platform suitable for future Majorana zero mode research.

Abstract

When a topological insulator is made into a nanowire, the interplay between topology and size quantization gives rise to peculiar one-dimensional states whose energy dispersion can be manipulated by external fields. In the presence of proximity-induced superconductivity, these 1D states offer a tunable platform for Majorana zero modes. While the existence of such peculiar 1D states has been experimentally confirmed, the realization of robust proximity-induced superconductivity in topological-insulator nanowires remains a challenge. Here, we report the realization of superconducting topological-insulator nanowires based on (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ (BST) thin films. When two rectangular pads of palladium are deposited on a BST thin film with a separation of 100--200 nm, the BST beneath the pads is converted into a superconductor, leaving a nanowire of BST in-between. We found that the interface is epitaxial and has a high electronic transparency, leading to a robust superconductivity induced in the BST nanowire. Due to its suitable geometry for gate-tuning, this platform is promising for future studies of Majorana zero modes.