Sputtered Mo-Re SQUID-on-Tip for High-Field Magnetic and Thermal Nanoimaging

Scanning nanoscale superconducting quantum interference devices (SQUIDs) have attracted attention as highly sensitive microscopic magnetic and thermal characterization tools of quantum and topological states of matter and devices. We present here a technique of collimated differential-pressure magnetron sputtering for the versatile self-aligned fabrication of SQUID-on-tip (SOT), which cannot be produced by conventional sputtering methods due to their diffusive, rather than the required directional point source, deposition. The technique provides access to a broad range of high H_c2 superconducting materials, alloys and possibly even high-Tc superconductors. This advancement is crucial for expanding the ranges of operating temperatures and magnetic fields essential of SOTs for the study of magnetic phenomena and dissipation mechanisms in a wide variety of quantum systems, unconventional superconductors, and topological materials. As a first example, we have fabricated Mo-Re SOTs with sub-50-nm diameter, that operates up to an unprecedentedly high magnetic field of 5 T with spin sensitivity better than 1.2 μ0/Hz1/2 up to 3 T at 4.2 K, and thermal sensitivity better than 4 μK/Hz1/2 up to 5 T—about five times higher than any previous report [1].

[1] K. Bagani et al., arXiv:1908.09305