Chirality-induced spin selectivity in chiral solids

Chirality-induced spin selectivity (CISS) has emerged as a striking phenomenon in which electron transport through chiral systems generates highly spin-polarized currents, even at room temperature and in the absence of a magnetic field or strong atomic spin-orbit coupling. While CISS has been intensively studied in molecular systems, its microscopic origin remains controversial, partly due to experimental limitations inherent to nanoscale molecules. In this review, the author focuses on CISS in chiral solids and introduces a classification into two categories based on time-reversal symmetry : CISS(I), a -even response associated with collinear current-induced spin polarization, and CISS(II), a -broken response involving antiparallel spin-pair formation under non-equilibrium conditions. The author further proposes an operational definition based on transport measurements, allowing direct comparison with experiments, including magnetoconductance studies in molecular systems. Recent experiments on chiral metals and superconductors are discussed in this framework, highlighting enhanced spin polarization, nonlocal spin transport, and symmetry conversion between structural and magnetic chirality. These results suggest that chiral solids provide a platform to bridge molecular and condensed-matter perspectives and to explore non-equilibrium spin-chirality coupling.