In situ transport measurements on ultrathin Bi(111) films using a magnetic tip: possible detection of current-induced spin polarization in the surface states

Abstract

We performed in situ transport measurements of ultrathin Bi(111) films grown on Si(111) surface, with a four-tip scanning tunneling microscope using metal-coated carbon nanotube (CNT) tips. When the distance between the current injection tip (nonmagnetic Pt-coated CNT tip) and voltage tip (magnetic CoFe-coated CNT tip) was smaller than 1 μ m, we found a violation of Green's reciprocity theorem which should hold with no spin transport. This was interpreted as a signal of the current-induced spin polarization (CISP) that occurs due to the Rashba spin-splitting surface-state bands of the Bi(111). The result was reasonably in accord with quantitative analyses based on the CISP theory of Rashba systems.