Masters defense: Thor Hvid-Olsen

Hybrid Double-Nanowire Devices

Parallel double nanowires (DNWs) coupled to superconductors could be applied for various experiments, including Majorana zero mode detection [7, 8, 3], Cooper pair splitting,[1, 5, 6] and topological Kondo effect investigations [2]. In this talk, it is presented how parallel InAs double nanowires with epitaxially grown superconducting Al is used as the base of device fabrication, applying electron lithography in combination with metal deposition and selective Al etch-
ing. During the presentation, specific challenges discovered in the fabrication process for double-nanowires, is outlined.
Following the presentation of the fabrication, DNW island devices and a DNW Josephson junction are analyzed. The DNW Josephson junction device shows phenomena, such as multiple Andreev reflections (MAR) and Fabry-Pérot oscillations. Furthermore supercurrent is found to run through both of the parallel Nanowires in the junction.
The DNW island devices are characterized, and shows superconductivity in terms of even-odd parity oscillations. The parity oscillations is found to be dependent on temperature and magnetic field. This dependency is attributed to quasiparticle excitations, and the parity oscillations are modelled, using a model from a similar device, based on a single nanowire, from Higginbotham et al.[4]. This model allows us to estimate parameters, such as the superconducting gap and a lower bound to the quasiparticle poisoning time.

References

[1] S. Baba, C. Junger, S. Matsuo, A. Baumgartner, Y. Sato, H. Kamata, K. Li, S. Jeppesen, L. Samuelson, H. Q. Xu, C. Schonenberger, and S. Tarucha. Cooper-pair splitting in two parallel InAs nanowires. New Journal of Physics, 20:8, 2018.

[2] B. Béri and N. R. Cooper. Topological Kondo Effect with Majorana Fermions. Physical Review Letters, 109(15), 2012

[3] Olesia Dmytruk, Manisha Thakurathi, Daniel Loss, and Jelena Klinovaja. Majorana bound states in double nanowires with reduced Zeeman thresholds due to supercurrents. Physical Review B, 99(24), 2019.

[4] A. Higginbotham, P., S. Albrecht, M., G. Kiršanskas, W. Chang, F. Kuemmeth, P. Krogstrup, T. Jespersen, S., J. Nygård, K. Flensberg, and C. Marcus, M. Parity lifetime of bound states in a proximitized semiconductor nanowire. Nature Physics, 11(12):1017–1021, 2015.