Control of Chirality, Spin, and Orbitals in Semiconductor-Based Chiral Molecular Devices*

Chirality-induced spin selectivity (CISS) is a phenomenon in which structural chirality can lead to different conductivities for electrons with opposite spins.[1] This intriguing effect has significant implications on the intricate interplay between structural chirality, electronic spin, and orbitals.

To obtain a comprehensive understanding of the underlying physical mechanisms of CISS and to demonstrate its potential device functionality, we have developed a robust device platform of chiral molecular junctions constructed on epitaxial magnetic and nonmagnetic semiconductors. Our approach involves the fabrication of normal metal/chiral molecules/semiconductor junctions and electrical measurements of the spin-valve effect [2,3] and Hanle effect [4]. The device design effectively addresses the issue of electrical shorting, thus enabling a systematic exploration of the physical origins of CISS as follows:

1. Our results provide definitive evidence for both nonlinear- and linear-response components in the bias-current dependences of the CISS spin-valve magnetoconductance;[2]

2. Through direct comparisons of chiral molecular spin valves utilizing Au and Al electrodes, our experiments demonstrate the essential roles of the spin-orbit coupling of the electrodes.[3] The result supports the theory that chiral molecules act as orbital polarizers, rather than spin filters;[5] and

3. CISS-induced Hanle effect is observed in junctions with conventional n-GaAs.[4] The Hanle amplitude displays distinctive scaling behavior with temperature and bias current. It highlights the potential for a novel scheme of semiconductor spintronics free of magnetic materials.

Our experiments have generated critical insights into the underlying physics of CISS and provided guidelines for its practical applications. In addition, our work emphasizes the need for clearer understanding of the key concepts of spin polarization in transport studies of CISS.[6]