Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces

Abstract

We characterize niobium-based lateral Superconductor (S) - Normal metal (N) - Superconductor weak links through low-temperature switching current measurements and tunnel spectroscopy. We fabricate the SNS devices in two separate lithography and deposition steps, combined with strong argon ion cleaning before the normal metal deposition in the last step. Our SNS weak link consists of high-quality sputtered Nb electrodes that are contacted with evaporated Cu. The two-step fabrication flow enables great flexibility in the choice of materials and pattern design. A comparison of the temperature-dependent equilibrium critical supercurrent with theoretical predictions indicates that the quality of the Nb-Cu interface is similar to that of evaporated Al-Cu weak links. Aiming at increased sensitivity, range of operation temperatures, and thermal isolation, we investigate how these SNS structures can be combined with shadow-evaporated aluminum tunnel junctions for sensor applications that utilize the superconducting proximity effect. To this end, we demonstrate a hybrid magnetic flux sensor based on a Nb-Cu-Nb SNS junction, where the phase-dependent normal metal density of states is probed with an Al tunnel junction.

5 pages, 3 figures

References in corpus (8)

• Phase controlled superconducting proximity effect probed by tunneling spectroscopy
• Fast electron thermometry towards ultra-sensitive calorimetric detection
• Proximity DC squids in the long junction limit
• Density of states and supercurrent in diffusive SNS junctions: role of nonideal interfaces and spin-flip scattering
• Highly-sensitive superconducting quantum interference proximity transistor
• Josephson current in nanofabricated V/Cu/V mesoscopic junctions
• Normal metal tunnel junction-based superconducting quantum interference proximity transistor: the N-SQUIPT
• Origin of Hysteresis in a Proximity Josephson Junction

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• High operating temperature in V-based superconducting quantum interference proximity transistors
• Thermal conductance of Nb thin films at sub-kelvin temperatures
• Microwave Admittance of Gold-Palladium Nanowires with Proximity-Induced Superconductivity
• Modification of electron-phonon coupling by micromachining and suspension
• Thouless energy in Josephson SN-N-NS bridges
• Inductive Superconducting Quantum Interference Proximity Transistor: the L-SQUIPT
• Magnetometry with low resistance proximity Josephson junction