On Local Sensing of Spin Hall Effect in Tungsten Films by Using STM-Based Measurements

The spin Hall effect (SHE) in tungsten films has been experimentally studied by using STM-based measurements. These measurements have been performed by using tungsten and iron-coated tungsten tips. In the case of tungsten tips, it has been observed that the current flow through the tungsten film results in an appreciable asymmetry in the tunneling current with respect to the change in the polarity of the tunneling voltage. It is reasoned that the cause of this asymmetry is the accumulation of spin polarized electrons on the tungsten film surface due to the spin Hall effect. This asymmetry is not affected by the change of the direction of the bias current through the film. However, in the case of iron-coated tungsten tips, it has been observed that a change in the direction of the bias current does lead to an additional asymmetry in the tunneling current. It is thus experimentally demonstrated that this asymmetry is caused by the SHE and spin-dependent density of the states of the iron-coated tips.