A Josephson junction based on a highly disordered superconductor/low-resistivity normal metal bilayer

Area of Science:

• Condensed Matter Physics
• Superconductivity
• Mesoscopic Physics

Background:

• Superconductor-normal metal-superconductor (SN-S-SN) Josephson junctions are crucial for quantum electronic devices.
• Understanding the current-phase relation (CPR) is key to controlling Josephson phenomena.
• Proximity-induced superconductivity in normal metal layers offers tunable junction properties.

Purpose of the Study:

• To calculate the current-phase relation (CPR) of SN-S-SN Josephson junctions.
• To investigate the influence of superconductor (S) and normal metal (N) layer thicknesses on CPR.
• To determine conditions for achieving a single-valued CPR and high critical current-resistance product (IcRn).

Main Methods:

• Numerical calculations of the CPR for SN-S-SN Josephson junctions.
• Modeling based on a bilayer structure of a highly disordered superconductor (S) and a normal metal (N) with proximity-induced superconductivity.
• Analysis of the impact of layer thicknesses and constriction length relative to the superconducting coherence length.

Main Results:

• A single-valued CPR, approaching a sinusoidal shape, is achieved when S and N layer thicknesses, and S constriction length are near the superconducting coherence length.
• The product IcRn can reach Δ(0)/2|e|, where Ic is critical current, Rn is normal-state resistance, and Δ(0) is the superconductor gap.
• Optimizing the N layer thickness results in nonhysteretic current-voltage characteristics even at low temperatures.

Conclusions:

• SN-S-SN Josephson junctions with optimized layer thicknesses exhibit desirable properties for applications.
• The N layer's role in phase concentration and heat dissipation is significant.
• Achieving a large IcRn product and nonhysteretic behavior is possible through careful material and geometric design.