Planar Josephson junctions based on few-layer black phosphorus
To date, Josephson junction (JJ) devices find a wide range of applications, such as extremely sensitive magnetometers, infrared sensors, single-photon detectors, for voltage metrology, and in superconducting circuits for quantum information technology. In particular, hybrid JJs formed by semiconductors placed in between two superconducting contacts have attracted great interest, due to the possibility of tuning superconducting properties by external electrostatic gates. In the study of 2D materials like graphene and its van der Waals relatives, recent advances in mechanical exfoliation techniques allowed for the fabrication of devices with monolayer thickness. This led in 2007 to the first fabrication and characterization of a graphene-based JJ device, demonstrating a bipolar tuning of supercurrent amplitude. Since then, a vast variety of graphene-superconductor hybrid structures have been explored, with an improved quality both of the graphene samples and in the transparency of the interfaces. This allowed to investigate proximity-induced superconductivity in graphene from the diffusive to the ballistic regime.
Graphene is only one example of the large family of van der Waals materials that can be exfoliated down to the monolayer. In spite of this, up to date, clear signatures of Josephson coupling in other van der Waals-based planar JJs have not been reported. We demonstrate the first planar JJ devices based on few layer black phosphorus (bP). bP is a layered semiconductor material, whose peculiar properties mainly stem from the anisotropic shape of its band structure, which affects both its electronic and optical properties. While bP itself is nor intrinsically superconducting, here we show that it can be proximitized by contact with a superconductor.
We present transport measurements on bP planar JJs with Nb contacts at cryogenic temperatures down to T = 33 mK, demonstrating, for the first time, supercurrent flow and clear evidence of Josephson coupling. The supercurrent can be controlled by a back gate. Application of a small perpendicular magnetic field leads to the formation of a well-developed Fraunhofer pattern. Supercurrent disappears above a temperature of 600 mK. All these observations are clear manifestations of proximity-induced superconductivity in the bP.
Figure 1: Differential resistance dV/dI of the junction as a function of bias current Isd and (a) back gate voltage Vbg, (b) magnetic field B, and (c) temperature T. The dashed red line in (b) indicates the fitted Fraunhofer pattern.
Publications:
- Giulio Cappelli: Quantum Transport in Planar Niobium/black-Phosphorus/Niobium Junctions, Master thesis, University of Pisa, 2020.
- Quantum Hall effect in hybrid Josephson junctions, NEST Scientific Report 2014 – 2020.
- Francesca Telesio, Matteo Carrega, Giulio Cappelli, Andrea Iorio, Alessandro Crippa, Elia Strambini, Francesco Giazotto, Manuel Serrano-Ruiz, Maurizio Peruzzini, Stefan Heun: Evidence of Josephson coupling in a few-layer black phosphorus planar Josephson junction, arXiv:2110.02877 [cond-mat.mes-hall].
- Francesca Telesio, Matteo Carrega, Giulio Cappelli, Andrea Iorio, Alessandro Crippa, Elia Strambini, Francesco Giazotto, Manuel Serrano-Ruiz, Maurizio Peruzzini, and Stefan Heun: Evidence of Josephson Coupling in a Few-Layer Black Phosphorus Planar Josephson Junction, ACS Nano 16 (2022) 3538 – 3545.
- F. Telesio, F. Mezzadri, M. Serrano-Ruiz, M. Peruzzini, F. Bisio, S. Heun, and F. Fabbri: Propagation of visible light in nanostructured niobium stripes embedded in a dielectric polymer, arXiv:2212.12296 [physics.optics].
- F. Telesio, F. Mezzadri, M. Serrano-Ruiz, M. Peruzzini, F. Bisio, S. Heun, and F. Fabbri: Propagation of visible light in nanostructured niobium stripes embedded in a dielectric polymer, Mater. Quantum Technol. 2 (2022) 045003.
Presented at:
- Giulio Cappelli: Quantum Transport in Planar Niobium/black-Phosphorus/Niobium Junctions, Master thesis defense, University of Pisa, 11 December 2020. [Talk]