Study of surface spin-polarized electron accumulation in topological insulators using scanning tunneling microscopy

We report the results of scanning tunneling microscopy experiments using iron-coated tungsten tips and current-carrying bismuth selenide (Bi $_2$ Se $_3$ ) samples. Asymmetry in tunneling currents with respect to the change in the direction of bias currents through Bi $_2$ Se $_3$ samples has been measured. It is argued that this asymmetry is the manifestation of surface spin-polarized electron accumulation caused by the 90 $^\circ$ electron spin–momentum locking in the topologically protected surface current mode. It is demonstrated that the manifestation of surface spin-polarized electron accumulation is enhanced by tin doping of Bi $_2$ Se $_3$ samples. Furthermore, we noted the appearance of spin-dependent density of states in current-carrying Bi $_2$ Se $_3$ samples.