Abstract
Superconducting quantum interference devices (SQUIDs) are currently used as magnetic flux detectors with ultra-high sensitivity for various applications such as medical diagnostics and magnetic material microstructure analysis. Single-crystalline superconducting boron-doped diamond is an excellent candidate for fabricating high-performance SQUIDs because of its robustness and high transition temperature, critical current density, and critical field. Here, we propose a fabrication process for a single-crystalline boron-doped diamond Josephson junction with regrowth-induced step edge structure and demonstrate the first operation of a single-crystalline boron-doped diamond SQUID above 2 K. We demonstrate that the step angle is a significant parameter for forming the Josephson junction and that the step angle can be controlled by adjusting the microwave plasma-enhanced chemical vapour deposition conditions of the regrowth layer. The fabricated junction exhibits superconductor–weak superconductor–superconductor-type behaviour without hysteresis and a high critical current density of 5800 A/cm2.
Highlights
Superconducting quantum interference devices (SQUIDs) are currently used as magnetic flux detectors with ultra-high sensitivity for various applications such as medical diagnostics and magnetic material microstructure analysis
The offset second transition temperature of 3.4 K means that the operating temperature of the Josephson junction was below 3.4 K; we evaluated the Josephson properties below 3.4 K, as described below
This structure is suitable for forming an superconductor–weak superconductor–superconductor (S–S′–S)-type non-hysteretic Josephson junction with a high critical current density using single-crystalline diamond
Summary
Superconducting quantum interference devices (SQUIDs) are currently used as magnetic flux detectors with ultra-high sensitivity for various applications such as medical diagnostics and magnetic material microstructure analysis. Single-crystalline superconducting boron-doped diamond is an excellent candidate for fabricating high-performance SQUIDs because of its robustness and high transition temperature, critical current density, and critical field. Boron-doped diamond shows potential for fabricating high-performance superconducting devices such as SQUIDs and mechanical resonators[14] because of its excellent characteristics and processability described below. In addition to the above excellent characteristics, diamond exhibits strong tolerance to oxidation, heating, and physical scratches, and its microfabrication using oxygen plasma etching or selective epitaxial growth is easy[23,26] These characteristics suggest the suitability of superconducting diamond for various device applications such as scanning SQUID microscope and strong coupled hybrid quantum systems[27,28,29] composed of nitrogen-vacancy centres[30] and superconducting circuits. We fabricated a single-crystalline boron-doped diamond Josephson junction with a regrowth step-edge structure. The details of the fabrication process and the properties are provided
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