SGM 13

Toward Quantum Hall Effect in a Josephson Junction

Recently, notions of electronic-band physics combined with typical tools of geometry and topology brought to the prediction of new states of matter, with potential applications in quantum technologies. First experimental evidence of topological states of matter goes back to the 1980s with the discovery of the quantum Hall (QH) effect. Here, the ultra-precise degree of conductance quantization is linked to the topological properties of the QH state. Indeed, owing to their non-trivial topology, metallic edge states are robust against disorder and weak perturbations and lead to the concept of topological protection. Among all applications exploiting this intrinsic robustness, the possibility to store quantum information in a stable fashion has recently played a major role. The recent discovery of new bound states with non-trivial braiding properties, such as Majorana states, renewed the interest in the study of hybrid superconductor (SC)/semiconductor systems. Among all, a promising candidate for hosting Majorana fermions is a QH state in proximity to a SC. Experimental evidence for the coexistence of superconductivity and QH is still scarce, however, different SC materials with large critical field can be envisioned that withstand magnetic fields sufficiently high to induce the QH regime in new hybrid devices. Indeed, very recently signatures of superconducting correlations in QH channels were reported in Josephson junctions (JJ) using graphene and III–V based 2D electron gas (2DEG).

We have fabricated JJ devices with a III-V high-mobility 2DEG interfaced with Nb superconducting contacts. Transport measurements demonstrate supercurrent flow and a critical temperature of 8.1 K, with critical fields as high as 3 T, see Fig. 1. Tuning of Josephson current is achieved by means of additional side gates. Furthermore, as shown in Fig. 2, the same samples support well-developed QH plateaus reaching filling factor v = 2 at B = 3 T. This demonstrates the potential of these hybrid devices to investigate the coexistence of SC and QH. We believe they can represent the first step in the development of new device architectures hosting topological states of matter.


Figure 1: (a) Change in resistance R_Nb as a function of temperature T. A sudden jump in the resistance is observed between T = 8.13 K and T = 8.15 K, indicating the transition from the superconductive to the normal state. The jump in resistance is about 8.8 Ω. B = 0 T. (b) Critical field of Nb, measured at T = 320 mK. For both measurements, I_ac = 800 nA and V_gate = 0 V.


Figure 2: (a) Conductance (in units of e^2/h) as a function of magnetic field. V_gate = 3 V. (b) Conductance as a function of V_gate, performed at B = 3 T. Resonances are highlighted with red arrows. T = 433 mK.

Moreover, we have fabricated a different, fully tunable, hybrid semiconductor/superconductor device, in which the width, area, and supercurrent of the two arms of a SQUID-like geometry can be independently controlled with high precision. In Fig. 3 we show that the device can be tuned from one extreme case to another: from a SQUID with narrow arms to a Fraunhofer pattern in an extended single–arm Josephson junction. Transition between these limits is investigated in a continuous manner, via electrostatic gating, without the need of additional in-plane magnetic field. These measurements are successfully analyzed within a theoretical model of an extended tunnel Josephson junction, taking into account the focusing factor of the setup. The wide tunability offered by this geometry, and its electrostatic control, is very promising for applications, and moreover it constitutes an easily scalable platform.


Figure 3: Differential resistance of the device as a function of the injected source-drain current and magnetic field in different configurations of asymmetric gate voltage. (a) Fraunhofer-type pattern, (b) SQUID-like pattern. T = 315 mK.

Publications:

  1. Stefano Guiducci: Electron transport and Scanning Gate Microscopy studies on hybrid ballistic SNS junctions, Master’s thesis, University of Pisa, Pisa, Italy 2014.
  2. Stefano Guiducci, Matteo Carrega, Giorgio Biasiol, Lucia Sorba, Fabio Beltram, Stefan Heun: Quantum Hall Effect in a Josephson Junction, arXiv:1805.02862 [cond-mat.mes-hall].
  3. Stefano Guiducci, Matteo Carrega, Giorgio Biasiol, Lucia Sorba, Fabio Beltram, Stefan Heun: Toward Quantum Hall Effect in a Josephson Junction, Phys. Status Solidi RRL 13 (2019) 1800222. Selected for the pss Showcase 2020.
  4. Stefano Guiducci, Matteo Carrega, Fabio Taddei, Giorgio Biasiol, Herve Courtois, Fabio Beltram, and Stefan Heun: Full electrostatic control of quantum interference in an extended trenched Josephson junction, arXiv:1903.02819 [cond-mat.mes-hall].
  5. S. Guiducci, M. Carrega, F. Taddei, G. Biasiol, H. Courtois, F. Beltram, and S. Heun: Full electrostatic control of quantum interference in an extended trenched Josephson junction, Phys Rev. B 99, 235419 (2019).
  6. M. Carrega, S. Guiducci, A. Iorio, L. Bours, E. Strambini, G. Biasiol, M. Rocci, V. Zannier, L. Sorba, F. Beltram, S. Roddaro, F. Giazotto, and S. Heun: Investigation of InAs-based devices for topological applications, arXiv:1909.12021 [cond-mat.mes-hall].
  7. M. Carrega, S. Guiducci, A. Iorio, L. Bours, E. Strambini, G. Biasiol, M. Rocci, V. Zannier, L. Sorba, F. Beltram, S. Roddaro, F. Giazotto, and S. Heun: Investigation of InAs-based devices for topological applications, Proc. of SPIE 11090 (2019) 110903Z-1.
  8. Matteo Carrega: Investigation of hybrid Josephson junctions for topological applications, CNR Nano Activity Report 2020 [Page 36].
  9. Quantum Hall effect in hybrid Josephson junctions, NEST Scientific Report 2014 – 2020.
  10. A. Benali, P. Rajak, R. Ciancio, J. R. Plaisier, S. Heun, and G. Biasiol: Metamorphic InAs/InGaAs Qws with electron mobilities exceeding 7 x 105 cm2/Vs, arXiv:2206.11590 [cond-mat.mtrl-sci].
  11. A. Benali, P. Rajak, R. Ciancio, J. R. Plaisier, S. Heun, and G. Biasiol: Metamorphic InAs/InGaAs Qws with electron mobilities exceeding 7 x 105 cm2/Vs, J. Cryst. Growth 593 (2022) 126768.
  12. O. Arif, L. Canal, E. Ferrari, C. Ferrari, L. Lazzarini, L. Nasi, A. Paghi, S. Heun, and L. Sorba: Influence of an overshoot layer on the morphological, structural, strain, and transport properties of InAs quantum wells, Nanomaterials 14 (2024) 592.

Presented at:

  1. Stefano Guiducci: Electron transport and Scanning Gate Microscopy studies on ballistic hybrid SNS junctions, Master thesis defense, University of Pisa, Italy, 22 October 2014. [Talk]
  2. S. Guiducci, M. Carrega, G. Biasiol, L. Sorba, F. Beltram, and S. Heun: Towards quantum Hall effect in a Josephson junction, Tunneling Through Nanoscience, Ravello, Italy, 17 – 20 October 2018 (invited). [Abstract] [Talk]
  3. Matteo Carrega, Stefano Guiducci, Giorgio Biasiol, Fabio Taddei, Lucia Sorba, Fabio Beltram, Stefan Heun: Investigation of hybrid Josephson junctions for topological applications, Materials.it 2018, Bologna, Italy, 22–26 October 2018 (invited). [Abstract] [Talk]
  4. Matteo Carrega, Stefano Guiducci, Giorgio Biasiol, Fabio Taddei, Lucia Sorba, Fabio Beltram, Stefan Heun: Towards topological applications with hybrid superconducting devices, NanoMeeting 2018, Pisa, Italy, 29 – 30 October 2018 (oral). [Abstract] [Talk]
  5. M. Carrega, S. Guiducci, G. Biasiol, F. Taddei, H. Courtois, L. Sorba, F. Beltram and S. Heun: Investigation of hybrid Josephson junctions for topological applications, E-MRS Spring Meeting 2019, Nice, France, 27 – 31 May 2019 (oral). [Abstract] [Talk]
  6. Matteo Carrega, Stefano Guiducci, Andrea Iorio, Lennart Bours, Elia Strambini, Giorgio Biasiol, Mirko Rocci, Valentina Zannier, Lucia Sorba, Fabio Beltram, Stefano Roddaro, Francesco Giazotto, and Stefan Heun: Investigation of InAs–based devices for topological applications, SPIE Nanoscience + Engineering, Spintronics XII Session, San Diego, California, United States, 11 – 15 August 2019 (invited). [Abstract] [Talk]
  7. M. Carrega, S. Guiducci, G. Biasiol, F. Taddei, H. Courtois, L. Sorba, F. Beltram, and S. Heun: Investigation of hybrid Josephson junctions for topological applications, FisMat 2019, Catania, Italy, 30 September – 4 October 2019 (oral). [Abstract] [Talk]
  8. A. Benali, P. Rajak, R. Ciancio, J. Plaisier, S. Heun, and G. Biasiol: Metamorphic InAs/InGaAs QWs with electron mobilities exceeding 7 x 105 cm2/Vs, 21st International Conference on Molecular Beam Epitaxy, 6 – 9 September 2021 (oral). [Abstract] [Talk]