  The spin activity in macromolecules such as DNA and oligopeptides, in the
context of the Chiral Induced Spin Selectivity (CISS) has been proposed to be
due to the atomic Spin-Orbit Coupling (SOC) and the associated chiral symmetry
of the structures. This coupling, associated with carbon, nitrogen and oxygen
atoms in biological molecules, albeit small (meV), can be enhanced by the
geometry, and strong local polarization effects such as hydrogen bonding (HB).
A novel way to manipulate the spin degree of freedom is by modifying the
spectrum using a coupling to the appropriate electromagnetic radiation field.
Here we use the Floquet formalism in order to show how the half filled band
Hamiltonian for DNA, can be modulated by the radiation to produce a up to a
tenfold increase of the effective SOC once the intrinsic coupling is present.
On the other hand, the chiral model, once incorporating the orbital angular
momentum of electron motion on the helix, opens a gap for different helicity
states (helicity splitting) that chooses spin polarization according to
transport direction and chirality, without breaking time reversal symmetry. The
observed effects are feasible in physically reasonable parameter ranges for the
radiation field amplitude and frequency.
