Theories of Chiral-Induced Spin Selectivity: A Pedagogical Overview.

The chiral-induced spin selectivity (CISS) effect refers to electron transport through chiral (often organic) molecules becoming spin-polarized, without external magnetic fields. While widely observed experimentally, a comprehensive theoretical understanding of the CISS effect remains to be developed. This review provides an accessible perspective on the effect and a summary of emerging CISS theories. We begin with fundamental concepts involving spin-orbit coupling, symmetries, and quantum transport. Then, we review key theoretical approaches, including scattering-based, tight-binding, vibration-assisted transport, strong-correlation, and chiral phonon models for CISS, while addressing crucial related aspects associated with hopping/tunneling mechanisms, angular momentum conservation, and experimental probes of CISS. Beyond molecular-scale processes, we explore CISS-related phenomena in solids, including the Rashba-Edelstein effect and electrical magnetochiral anisotropy. By bridging molecular and solid-state perspectives, we aim to lower the barrier of entry for theoretical researchers interested in this exciting topic.