Gate-tunable supercurrent and multiple Andreev reflections in a superconductor-topological insulator nanoribbon-superconductor hybrid device

TL;DR

This study demonstrates gate-tunable superconductivity and multiple Andreev reflections in a topological insulator nanoribbon Josephson junction, revealing high contact transparency and potential for topologically protected quantum devices.

Contribution

It reports the first observation of gate-tunable proximity-induced superconductivity and high-order Andreev reflections in a BiSbTeSe$_2$ nanoribbon Josephson junction with Nb contacts.

Findings

Gate-tunable critical current up to 430 nA.

Observation of multiple Andreev reflection peaks up to order n=13.

High contact transparency indicated by high-order MARs.

Abstract

We report on the observation of gate-tunable proximity-induced superconductivity and multiple Andreev reflections (MAR) in a bulk-insulating BiSbTeSe$_2$ topological insulator nanoribbon (TINR) Josephson junction (JJ) with superconducting Nb contacts. We observe a gate-tunable critical current ($I_C$) for gate voltages ($V_g$) above the charge neutrality point ($V_{CNP}$), with $I_C$ as large as 430 nA. We also observe MAR peaks in the differential conductance ($dI/dV$) versus DC voltage ($V_{dc}$) across the junction corresponding to sub-harmonic peaks (at $V_{dc} = V_n = 2\Delta_{Nb}/en$, where $\Delta_{Nb}$ is the superconducting gap of the Nb contacts and $n$ is the sub-harmonic order). The sub-harmonic order, $n$, exhibits a $V_g$-dependence and reaches $n = 13$ for $V_g = 40$ V, indicating the high transparency of the Nb contacts to TINR. Our observations pave the way toward exploring the possibilities of using TINR in topologically protected devices that may host exotic physics such as Majorana fermions.