SGM 21

Half-integer Shapiro steps in InSb/Nb Josephson junctions

InSb is a high-quality narrow band gap semiconductor with strong spin-orbit coupling, which makes it the ideal platform to develop architectures able to coherently control new states of matter with topological properties. We present transport data on hybrid Josephson junctions made from InSb nanoflags with Nb contacts. These InSb nanoflags have a typical size of L ~ 2.8 μm, W ~ 500 nm, and d ~ 100 nm. A mobility of 29.500 cm2/(Vs) at an electron density of 8.5 × 1011 cm-2 is measured, which results in an electron mean free path ℓ𝑒 ~ 500 nm. At variance to previous work, in the junctions presented here the Nb is directly deposited on the S-passivated InSb nanoflags.

The junction discussed in the following has a length L of 80 nm and a width W of 700 nm. Since ℓ𝑒 > 𝐿, the transport in the junction is ballistic. The Nb has a critical temperature of ~ 8.9 K. This corresponds to a BCS gap of ~ 1.3 meV, so that the induced superconducting coherence length exceeds L, which places the device in the short-junction limit. At 30 mK, the junction shows a critical current above 100 nA. The temperature dependence of the critical current above 500 mK is well described by a short-junction model with interface transparency 0.93. However, a detailed analysis of the full temperature range suggests that the current in the junction is the sum of the short channel contribution and a long channel contribution, for which a path length of about 3.5 μm is obtained (Fig. 1a). This result is consistent with the quantitative analysis of the anomalous Fraunhofer pattern measured on the same junction (Fig. 1b). Finally, irradiating the junction with microwaves, half-integer Shapiro steps are observed (Fig. 1c), which are robust in temperature and persist up to 1 K, suggesting their possible nonequilibrium origin.

Figure 1: (a) Temperature dependence of the critical current. (b) Anomalous Fraunhofer pattern. (c) Half-integer Shapiro steps.

Publications:

  1. Andrea Iorio, Alessandro Crippa, Bianca Turini, Sedighe Salimian, Matteo Carrega, Luca Chirolli, Valentina Zannier, Lucia Sorba, Elia Strambini, Francesco Giazotto, Stefan Heun: Half-integer Shapiro steps in highly transmissive InSb nanoflag Josephson junctions, arXiv:2303.05951 [cond-mat.supr-con].
  2. Andrea Iorio: Superconducting circuits with metallic and semiconducting weak-links, PhD Thesis, Scuola Normale Superiore, Pisa, Italy, 2023.
  3. A. Iorio, A. Crippa, B. Turini, S. Salimian, M. Carrega, L. Chirolli, V. Zannier, L. Sorba, E. Strambini, F. Giazotto, and S. Heun: Half-integer Shapiro steps in highly transmissive InSb nanoflag Josephson junctions, Phys. Rev. Res. 5 (2023) 033015.
  4. Highly transmissive InSb nanoflag Josephson junctions, CNR Nano Activity Report 2024. [Pages 62-63]

Presented at:

  1. Stefan Heun: Non-equilibrium microwave induced supercurrents in highly transmissive InSb nanoflag Josephson junctions, AndQC Meeting, Basel (Switzerland), 2-3 March 2023. [Talk]
  2. A. Iorio, A. Crippa, B. Turini, S. Salimian, M. Carrega, L. Chirolli, V. Zannier, L. Sorba, E. Strambini, F. Giazotto, and S. Heun: Half-integer Shapiro steps in highly transmissive InSb nanoflag Josephson junctions, Hybrid Quantum Technologies Workshop 2023, Klosterneuburg/Vienna (Austria), 3–6 April 2023. [Abstract] [Poster]
  3. A. Iorio, B. Turini, S. Salimian, M. Carrega, L. Chirolli, A. Crippa, E. Strambini, V. Zannier, L. Sorba, F. Giazotto, and S. Heun: Half-integer Shapiro steps in InSb /Nb Josephson junctions, Bound States 2023, Budapest (Hungary), 11-14 June 2023. [Abstract] [Talk]
  4. A. Iorio: Superconducting circuits with metallic and semiconducting weak-links, PhD thesis defense, Scuola Normale Superiore, Pisa, Italy, 22 September 2023. [Talk]
  5. S. Heun: Highly transmissive InSb nanoflag Josephson junctions, ISSP, The University of Tokyo, Japan (Prof. Y. Hasegawa), 5 October 2023. [Abstract] [Talk]
  6. A. Iorio, B. Turini, S. Salimian, A. Crippa, E. Strambini, V. Zannier, M. Carrega, L. Chirolli, F. Beltram, L. Sorba, F. Giazotto, and S. Heun: Highly transmissive InSb nanoflag Josephson junctions, NQSTI Workshop, Rome, Italy, 15 – 16 January 2024 (oral). [Abstract] [Talk]
  7. A. Iorio, A. Crippa, B. Turini, S. Salimian, M. Carrega, L. Chirolli, V. Zannier, L. Sorba, E. Strambini, F. Giazotto, and S. Heun: Half-integer Shapiro steps in highly transmissive InSb nanoflag Josephson junctions, DPG Spring Meeting, Berlin, Germany, 17 – 22 March 2024 (oral). [Abstract] [Talk]
  8. S. Heun: Hybrid superconductor – semiconductor Josephson junctions for quantum technologies, Workshop Il CNR nel panorama regionale delle Scienze e Technologie Quantistiche, Naples, Italy, 7 June 2024 (invited). [Abstract] [Talk]
  9. S. Heun: Josephson junctions based on high mobility InSb nanoflags for advanced quantum technologies, Workshop on Non-equilibrium quantum many-body systems, Genoa, Italy, 10 – 12 July 2024. [Abstract] [Talk]