Signatures of Majorana fermions in superconductor-semiconductor nanowire-superconductor quantum devices

‡Division of Solid State Physics Lund University, Box 118, S-22100 Lund, Sweden

§Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China

We report on the observation of the signatures of Majorana fermions in superconductor-semiconductor quantum dot-superconductor hybrid devices. The devices are made from high crystal-quality InSb nanowires and superconductor Nb contacts. The InSb nanowires are known to have excellent physical properties [1-3] and have therefore been considered as one of the most promising material systems for realizing topological superconductor systems in which Majorana fermions can be created. In a fabricated device, an InSb nanowire quantum dot is formed between the two Nb contacts by weak Schottky barriers. Due to the proximity effect, the InSb nanowire segments covered by superconductor Nb contacts turn to superconductors with a superconducting energy gap Δ* [4]. Under an applied magnetic field larger than a critical value for which the Zeeman energy in the InSb nanowire is Ez ~ Δ*, the entire InSb nanowire is found to be in a nontrivial topological superconductor phase, supporting a pair of Majorana fermions, and Cooper pairs can transport between the superconductor Nb contacts via the Majorana fermion states. This transport process will be suppressed when the applied magnetic field becomes larger than a second critical value at which the transition to a trivial topological superconductor phase occurs in the system. This physical scenario has been observed in our experiment [4]. We have also found that the measured zero-bias conductance for our hybrid devices shows a conductance plateau in a range of applied magnetic fields in quasi-particle Coulomb blockade regions [4]. Our work provides a simple, solid way of detecting Majorana fermions in solid state systems and should greatly stimulate Majorana fermion research and applications.

The author acknowledges collaborations with Mingtang Deng, Chunlin Yu, Guangyao Huang, Marcus Larsson, and Philippe Caroff for this work.

[1] H. A. Nilsson, P. Caroff, C. Thelander, M. Larsson, J. B. Wagner, L.-E. Wernersson, L. Samuelson, and H. Q. Xu. Nano Lett. 9, 3151–3156 (2009).
[2] H. A. Nilsson, O. Karlström, M. Larsson, P. Caroff, J. N. Pedersen, L. Samuelson, A. Wacker, L.-E. Wernersson, and H. Q. Xu. Phys. Rev. Lett. 104, 186804 (2010).
[3] H. A. Nilsson, P. Samuelsson, P. Caroff, and H. Q. Xu, Nano Lett.12, 228-233 (2012).
[4] M. T. Deng, C. L. Yu, G. Y. Huang, M. Larsson, P. Caroff, and H. Q. Xu, http://arxiv.org/abs/1204.4130 (2012).