Chirality-induced spin selectivity without intrinsic spin-orbit coupling: Role of current-induced molecular orbital moment

The microscopic origin of the chirality-induced spin selectivity (CISS) in helical molecules remains an open question. Recent experiments suggest that a significant contribution to CISS arises from the molecule itself, which is disregarded in existing interfacial or scattering based theories. Here we present an alternative theory of CISS to address this molecular contribution. The mechanism is based on the circulation of charge current in molecular loops that generates a molecular orbital moment (MOM). The direction of the MOM is governed by the gauge field arising from the structural distortion of the molecule and is associated with the handedness of the molecule. Such a MOM can produce finite CISS magnetoresistance and magnetochiral conductance asymmetries that are even in bias voltage, without violating the Onsager-Casimir reciprocity relations. Depending on the Fermi level and bias voltage, the MOM can be controlled externally, which can result in additional crossings of the enantiomer $I-V$ curves. Finally we explain the origin of the electrical magnetochiral anisotropy within the same framework, which establishes its generic applicability.