Crossover from Josephson effect to single interface Andreev reflection in asymmetric superconductor/nanowire...

Area of Science:

• Superconducting electronics
• Nanowire device physics
• Quantum phenomena in condensed matter

Background:

• Josephson junctions are fundamental to superconducting electronics, enabling applications like sensitive magnetometers and quantum bits.
• Nanowire-based Josephson junctions offer tunable properties and potential for miniaturization.
• Understanding the behavior of superconducting materials like aluminum (Al) and niobium (Nb) in nanowire geometries is crucial for advancing quantum technologies.

Purpose of the Study:

• To fabricate and characterize symmetric (Al- and Nb-based) and asymmetric (Al/InAs-nanowire/Nb) Josephson junctions.
• To investigate the Josephson supercurrent and subharmonic gap structures in these devices.
• To explore the switching behavior of asymmetric junctions under external magnetic fields or temperature variations and observe associated quantum phenomena.

Main Methods:

• Fabrication of symmetric and asymmetric Josephson junctions using superconducting materials (Al, Nb) and InAs nanowires.
• Characterization of junction properties through electrical transport measurements.
• Application of magnetic fields and temperature variations to probe device behavior and switching phenomena.

Main Results:

• Observation of clear and pronounced Josephson supercurrents in symmetric Al- and Nb-based junctions.
• Detection of subharmonic gap structures in symmetric junctions, indicating coherent quantum effects.
• Confirmation of Josephson coupling in asymmetric Al/InAs-nanowire/Nb junctions at zero magnetic field.
• Demonstration of switching asymmetric junctions to a single-interface superconductor/nanowire structure by exceeding the critical field of Al or critical temperature of Al.
• Observation of a pronounced zero-bias conductance peak in the switched state, attributed to reflectionless tunneling.

Conclusions:

• Symmetric and asymmetric nanowire-based Josephson junctions can be successfully fabricated and exhibit characteristic superconducting properties.
• The observed phenomena, including Josephson supercurrents, subharmonic gap structures, and reflectionless tunneling, highlight the potential of these devices for fundamental studies and future applications in quantum electronics.
• The ability to switch asymmetric junctions to a single-interface configuration provides a novel pathway for controlling and probing quantum transport in hybrid superconductor-semiconductor systems.