Observation of edge and bulk states in a three-site Kitaev chain

TL;DR

This study demonstrates the existence and control of Majorana bound states in a minimal three-site Kitaev chain using semiconductor-superconductor hybrid systems, confirming theoretical predictions through tunneling spectroscopy.

Contribution

The paper provides experimental evidence of edge and bulk state correlation in a three-site Kitaev chain, validating key theoretical predictions about Majorana bound states.

Findings

Zero-bias conductance peaks at outer QDs are correlated with an excitation gap in the middle QD.

The excitation gap can be tuned by a superconducting phase difference.

Majorana bound states are robust only when the excitation gap is present.

Abstract

A chain of quantum dots (QDs) in semiconductor-superconductor hybrid systems can form an artificial Kitaev chain hosting Majorana bound states (MBSs). These zero-energy states are expected to be localised on the edges of the chain, at the outermost QDs. The remaining QDs, comprising the bulk, are predicted to host an excitation gap that protects the MBSs at the edges from local on-site perturbations. Here we demonstrate this connection between the bulk and edges in a minimal system, by engineering a three-site Kitaev chain in a two-dimensional electron gas. Through direct tunneling spectroscopy on each site, we show that the appearance of stable zero-bias conductance peaks at the outer QDs is correlated with the presence of an excitation gap in the middle QD. Furthermore, we show that this gap can be controlled by applying a superconducting phase difference between the two hybrid segments and that the MBSs are robust only when the excitation gap is present. We find a close agreement between experiments and the original Kitaev model, thus confirming key predictions for MBSs in a three-site chain.