Fabrication and Application of Nano-SQUID Magnetometer to Scanning Imaging of Two-Dimensional Quantum Materials

Superconducting quantum interference devices (SQUIDs) are directly sensitive to magnetic flux. Nano-fabricated SQUID chip with miniaturized superconducting circuits can be further utilized as scanning probes for imaging of materials. Scanning SQUID microscopy (SSM) combines both high spatial resolution and high magnetic field sensitivity and is especially suitable for studying low dimensional materials with small sensing volumes. Here, we briefly review the fabrication of different types of nano-SQUIDs and the recent progress of utilizing them for scanning microscopy of quantum materials. We focus on but are not limited to topological states, unconventional superconductivity and exotic magnetism with a particular interest in two-dimensional materials. The magnetometry, susceptometry and current imaging modes of the SSM coupled with the external tuning of the material by magnetic field, electrical field gating and strain reveals a multitude of information beyond the scopes of charge-sensing probes.