Pb/InAs Nanowire Josephson Junction with High Critical Current and Magnetic Flux Focusing

Abstract

We have studied mesoscopic Josephson junctions formed by highly n-doped InAs nanowires and superconducting Ti/Pb source and drain leads. The current-voltage properties of the system are investigated by varying temperature and external out-of-plane magnetic field. Superconductivity in the Pb electrodes persists up to ∼ 7 K and with magnetic field values up to 0.4 T. Josephson coupling at zero backgate voltage is observed up to 4.5 K and the critical current is measured to be as high as 615 nA. The supercurrent suppression as a function of the magnetic field reveals a diffraction pattern that is explained by a strong magnetic flux focusing provided by the superconducting electrodes forming the junction.

On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In0.75Ga0.25As‐Quantum‐Well–Nb Josephson Junctions

“…Therefore, in each junction we have a small area of A = L × w = 3.4 µm 2 with induced superconductivity that is bounded to large areas of ≈100 µm 2 in each side of the junction where they are in the normal state. A similar result was also reported in 2DEG (hybrid NbNGaAs-NbN) [6] as well as nanowire (hybrid Ti/Pb-InAs-Ti/Pb) [18] Josephson junction systems.…”

“…[15,18] This comes from the expelled flux that is pushed into this area due to the screening currents in each Nb electrodes because of the Meissner state in low fields. Figure 4a shows an oscillation of ΔB ≈ 0.8 mT which approximately corresponds to an area of ≈ΔΦ/ΔB ≈ 2.5 µm 2 .…”

“…This does not fit with the expected enhancement of field due to field focusing. [18] The applied magnetic field here is far from the critical filed of Nb so the system is expected to be in full Meissner regime. The following reasons may explain this deviation: i) dephasing from the normal 2DEG regions either side of the junction which reduces the junction's area considerably, and ii) a small amount of static magnetic disorder, and in the 2DEG there is a region formed that acts as quantum dots with an odd number of electrons.…”

Superconducting transport in single and parallel double InAs quantum dot Josephson junctions with Nb-based superconducting electrodes

“…We have recently observed increased switching current for parallel double quantum dot Josephson junctions (DQDJJs) with Al electrodes when both dots are on resonance, indicating split but correlated Cooper pair tunneling through the two dots 15 . To further study the spin correlation in the split tunneling of paired electrons it is proposed to detect the phase factor in two path interference [16][17][18] , for which parallel double [19][20][21][22][23][24][25][26] . In this study we report the fabrication and characterization of Nb-based self-assembled QDJJs, in which gatetunable InAs single and double SAQDs are utilized.…”

“…Being a refractory metal with high melting point it is unsuitable for electron beam deposition without significant efforts to reduce the risk of oxygen contamination (for example due to outgassing resist) which can drastically effect the superconducting properties for small structures. Indeed there have been no reports on fabrication of QDJJs with InAs SAQDs contacted by electrodes made from Nb or other large superconducting gap materials to date, whereas there are a number of reports on InAs or InSb nanowires coupled to such superconductors [19][20][21][22][23][24][25][26] . In this study we report the fabrication and characterization of Nb-based self-assembled QDJJs, in which gatetunable InAs single and double SAQDs are utilized.…”