Spontaneous spin selectivity in chiral molecules at the interface
Chirality-induced spin selectivity (CISS) has been extensively studied over the past two decades. While current-induced spin polarization in chiral molecules is widely recognized as the fundamental principle of the CISS, only a few studies have been reported on bias-current-free CISS, where there is no bias electric current in chiral molecules. Recent studies on the chirality-induced exchange bias and current-in-plane magnetoresistance (CIP-MR) effects using chiral molecule/ferromagnet bilayer systems indicate that chiral molecules at the interface possess thermally driven broken-time-reversal symmetry, which induces bias-current-free CISS, i.e. a spontaneous effective magnetic field in the system. In this paper, we briefly review CISS-related phenomena in terms of the symmetry and discuss the mechanism of bias-current-free CISS. We also discuss the possibility of the linear magnetoelectric effect of chiral molecules, which arises from the spin polarization at the edges of molecules with metallic contacts, and its potential impact on the observed CISS phenomena.