Progress Toward Low Temperature Spin Hall STM Measurements

The Spin-Hall effect has been observed¹ in room-temperature polycrystalline tungsten films through scanning tunneling microscope (STM) measurements with both tungsten and iron-coated tungsten tips. When a lateral current is passed through the film, spin-polarized electrons accumulate on the surface which creates an asymmetry in the tunneling current with respect to the polarity of the sample bias. Furthermore, the use of an iron-coated tip results in an additional asymmetry which depends on the direction of the lateral current flow. We seek to extend these observations to topological insulators such as Bi2Se3 and PbSnTe under cryogenic conditions. We have implemented a new sample holder design for our low-temperature (4 K) STM, and are in the process of upgrading our system to operate at 1 K. This opens the door to performing dI/dV spectroscopy on spin-polarized topological materials as well as measuring atomic-scale lateral variations in the spin current.

[1] Xie, Ting & Dreyer, Michael & Bowen, D. & Hinkel, D. & Butera, R.E. & Krafft, Charles & Mayergoyz, Isaak. (2017). On local sensing of Spin Hall effect in tungsten film by using STM-type tunneling. 1-1. 10.1109/INTMAG.2017.8007778.