Subgap spectroscopy along hybrid nanowires by nm-thick tunnel barriers
Vukan Levajac (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Kouwenhoven Lab)
Ji Yin Wang (Beijing Academy of Quantum Information Sciences, Beijing, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Kouwenhoven Lab)
Cristina Sfiligoj (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - BUS/Quantum Delft)
Mathilde Lemang (TU Delft - QN/Afdelingsbureau, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Jan Cornelis Wolff (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Kouwenhoven Lab)
Alberto Bordin (TU Delft - QuTech Advanced Research Centre, TU Delft - QRD/Kouwenhoven Lab, Kavli institute of nanoscience Delft)
Ghada Badawy (Eindhoven University of Technology)
Sasa Gazibegovic (Eindhoven University of Technology)
Erik P.A.M. Bakkers (Eindhoven University of Technology)
Leo P. Kouwenhoven (TU Delft - QuTech Advanced Research Centre, TU Delft - QN/Kouwenhoven Lab, Kavli institute of nanoscience Delft)
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Abstract
Tunneling spectroscopy is widely used to examine the subgap spectra in semiconductor-superconductor nanostructures when searching for Majorana zero modes (MZMs). Typically, semiconductor sections controlled by local gates at the ends of hybrids serve as tunnel barriers. Besides detecting states only at the hybrid ends, such gate-defined tunnel probes can cause the formation of non-topological subgap states that mimic MZMs. Here, we develop an alternative type of tunnel probes to overcome these limitations. After the growth of an InSb-Al hybrid nanowire, a precisely controlled in-situ oxidation of the Al shell is performed to yield a nm-thick AlOx layer. In such thin isolating layer, tunnel probes can be arbitrarily defined at any position along the hybrid nanowire by shadow-wall angle-deposition of metallic leads. In this work, we make multiple tunnel probes along single nanowire hybrids and successfully identify Andreev bound states (ABSs) of various spatial extension residing along the hybrids.
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