Scanning SQUID microscopy in a cryogen-free dilution refrigerator.

Area of Science:

• Condensed Matter Physics
• Quantum Sensing
• Cryogenic Engineering

Background:

• Superconducting Quantum Interference Devices (SQUIDs) are highly sensitive magnetometers.
• Achieving millikelvin temperatures is crucial for studying quantum phenomena.
• Cryogen-free systems offer advantages in accessibility and operational simplicity.

Purpose of the Study:

• To develop and demonstrate a scanning SQUID microscope capable of operation at millikelvin temperatures in a cryogen-free environment.
• To achieve micrometer-scale magnetic imaging resolution.
• To enable simultaneous measurement of static magnetic fields, magnetic susceptibility, and current-induced magnetic fields.

Main Methods:

• Integration of a scanning SQUID microscope into a cryogen-free dilution refrigerator.
• Rigid mounting of the microscope to the mixing chamber for optimal thermal anchoring.
• Implementation of vibration isolation techniques and a rigid microscope housing.
• Operation within a superconducting vector magnet.
• Simultaneous acquisition of multiple magnetic field signals.

Main Results:

• Successful operation of the SQUID microscope at a base temperature of at least 30 mK.
• Achieved micrometer resolution imaging over a 150 µm range with stable base temperature.
• Demonstrated simultaneous imaging of static magnetic fields, magnetic susceptibility, and current-induced fields.
• Minimized relative vibrations between the SQUID sensor and the sample.

Conclusions:

• The developed cryogen-free scanning SQUID microscope provides a versatile platform for high-resolution magnetic imaging at millikelvin temperatures.
• The system enables detailed characterization of superconducting devices and quantum materials.
• This technology advances the study of nanoscale magnetic phenomena in accessible cryogenic conditions.