Spin Filtering through Chiral Molecules on Semiconductors

The effect of chirality-induced spin selectivity has been observed in a host of nanostructures involving chiral molecule monolayers on noble metals.¹ However, there has been no report of similar experiments on semiconductor (SC) surfaces. Here, we report on a study of spin-selective electron transport across chiral polyalanine molecules in vertical junctions of (Ga,Mn)As/polyalanine/Au. The bottom electrode is an epitaxially strained (Ga,Mn)As film with perpendicular magnetic anisotropy. The junctions are formed in openings in a hardened PMMA layer on the (Ga,Mn)As defined by electron beam lithography. The native oxide on the exposed (Ga,Mn)As is removed by ion milling, followed immediately by polyalanine monolayer self-assembly in a solution. The top Cr/Au electrodes are thermally evaporated under liquid nitrogen cooling. The (Ga,Mn)As acts as a spin analyzer: Sweeping the perpendicular magnetic field at low temperatures, sharp jumps in the junction resistance are observed at the coercive fields, indicating spin filtering of electrons from the Au electrode by the polyalanine monolayer. The result implies a potential approach to realize spin injection and detection on SCs without using any magnetic material.

¹ R. Naaman and D.H. Waldeck, Annu. Rev. Phys. Chem. 66, 263 (2015).