Terahertz-induced Berry curvature control of spin-selective transport in chiral DNA molecules.

CONTEXT: Chirality-induced spin selectivity (CISS) represents a remarkable quantum phenomenon whereby electron transmission through chiral molecules, such as DNA, becomes intrinsically spin-polarized even in the absence of magnetic fields. Despite extensive experimental verification of static CISS effects, achieving dynamic control over spin polarization remains an open challenge. Terahertz (THz) radiation offers a promising route to externally modulate molecular electronic structure on sub-picosecond timescales. In this study, we develop a theoretical model that unifies THz-driven Floquet dynamics with the spin-orbit coupling inherent to chiral DNA, thereby introducing the concept of Floquet-CISS, a light-induced regime of topologically controlled spin transport in biological helices.

METHOD: An effective low-energy Hamiltonian incorporating kinetic motion along the DNA helix, spin-orbit coupling, and the interaction with circularly polarized THz fields was formulated and solved using Floquet theory. The resulting quasi-energy spectra, Berry curvature, and spin polarization were numerically evaluated using plane-wave expansion and LAPACK-based diagonalization. The simulations reveal that THz fields dynamically reshape the Berry curvature, induce tunable spin-split Floquet bands, and produce helicity-dependent spin polarization exceeding 60%. These effects arise entirely from light-matter coupling without magnetic components, establishing DNA as a bio-topological spin filter capable of ultrafast, reversible spin control. The Floquet-CISS mechanism provides a theoretical blueprint for THz-programmable molecular spintronics and paves the way toward optically reconfigurable bio-quantum devices.