Imaging of Gate-Controlled Suppression of Superconductivity by Scanning Nitrogen-Vacancy Magnetometry

Scanning nitrogen-vacancy microscopy (SNVM) has emerged as a unique tool for investigating nanoscale magnetism with high sensitivity and sub-50-nm spatial resolution. While mostly applied at room temperature, the SNVM can be extended to the cryogenic regime down to millikelvin (mK) temperatures, allowing for the study of superconducting systems. Using mK-SNVM, we characterize gate-controlled suppression of superconductivity (GCS) in gated Nb islands by spatially imaging the Meissner screening. We demonstrate micrometer-scale suppression of superconductivity in the Nb island in proximity to the gate contact and correlate the size of the quenched area with experimental parameters such as the power dissipated at the gate and the sample temperature. The project demonstrates the GCS effect without relying on transport measurements for the first time and yields insights into the microscopic mechanisms of the effect.