Spin-polarized scanning tunneling microscopy using optically pumped GaAs tips

We have developed micro-fabricated GaAs tips for application to spin-polarized scanning tunneling microscopy (SP-STM). In the case of SP-STM measurements using the GaAs tip and a magnetic sample, the tunneling current slightly changes by switching between right and left circularly polarized light pumping, i.e. the different current component includes a spin-dependent signal of the sample surface. However, this difference of the tunneling current is easy to fluctuate and frequently depends on a topographic component. In this study, the polarized light modulation method and the tunneling current detection method are improved. As a result, the spin-dependent tunneling spectra can be detected reproducibly, and the topography-dependent signal is also suppressed successfully in the SP-STM imaging.