Chirality-induced spin selectivity due to an emergent molecular orbital moment

Abstract

The microscopic origin of chirality-induced spin selectivity (CISS), a phenomena where chiral molecules connected to a magnetic electrode show large spin-dependent conductance asymmetry even in ambient temperature, still remains an open question. Most of the existent theories are based on some sort of effective spin-orbit coupling or interfacial scattering, which do not provide satisfactory explanations for experimental observations such as the magnitude of spin polarization or the length dependence of the effect. We propose an alternative theoretical framework rooted in an intrinsic molecular contribution that shows a robust CISS effect and scales with the length of the molecule. The mechanism is based on the emergent molecular magnetic moment (MOM), which can produce experimentally observed point-symmetric I-V curves without violating the Onsager-Casimir reciprocity relation. The MOM has an intrinsic component that is governed by the chirality of the molecule and leads to finite CISS magnetoresistance and magnetochiral conductance asymmetry (MChA) that are even in bias voltage. By decomposing the MOM into its Fermi sea and Fermi surface components, we show that under strong bias, the MOM can be dominated by the Fermi surface contribution, which causes a sign change in the MChA leading to a behavior similar to that of electric magnetochiral anisotropy (eMChA). Finally, we analyze the effect of a magnetic field within the same framework, which may provide better insight into the crossover between CISS and eMChA.

arXiv comment13 pages, 12 figures, 4 appendices