Observation of edge and bulk states in a three-site Kitaev chain
Sebastiaan L.D. ten Haaf (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Goswami Lab)
Yining Zhang (Kavli institute of nanoscience Delft, TU Delft - QRD/Goswami Lab, TU Delft - QuTech Advanced Research Centre)
Qingzhen Wang (TU Delft - QRD/Goswami Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Alberto Bordin (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Kouwenhoven Lab)
Chun Xiao Liu (Kavli institute of nanoscience Delft, Student TU Delft)
Ivan Kulesh (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QRD/Goswami Lab)
Vincent P.M. Sietses (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Kouwenhoven Lab)
Christian G. Prosko (TU Delft - QRD/Kouwenhoven Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Michael Wimmer (TU Delft - QN/Wimmer Group, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Wimmer Group)
Srijit Goswami (TU Delft - QRD/Goswami Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
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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 localized 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 tunnelling 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.