High Spin Resolution Scanning Tunneling Spectroscopy Using Superconducting Tip

We demonstrate spin-polarized scanning tunneling spectroscopy (SP-STS) with high spin resolution, achieved using two types of superconducting tips : a conventional superconducting tip and a Yu-Shiba-Rusinov (YSR) tip, which is created by decorating a single magnetic atom at the apex of a superconducting tip. Owing to their nearly full spin polarization of the density of states, both tips enable quantitative and highly sensitive measurements of the spin polarization of the sample. These techniques provide powerful means for probing emergent quantum phenomena that demand ultrahigh spin sensitivity, including the spin polarization of Majorana zero modes around vortex cores in topological superconductors.