Theory of Doping chiral materials for switching chirality and spin polarization

Switching of chirality has been realized in chiral molecules, enabling applications as controllable units for spin selectivity and optical circular polarization. We turn our focus from chirality in molecules to chirality in solid crystals. The challenge is that all chiral units in the crystal need to be switched simultaneously. To do so we utilize carrier doping in crystals as a tool for controlling properties of the non-chiral segments which should equally affect all chiral units in transforming the chiral phase while switching chirality units in the crystal. We study via DFT doping theory the possibility of controlling all chiral units in a chiral solid. The test system is a wide-gap window material chiral SiO₂. The effect on the barrier was tested by monitoring the activation barrier between the two chiral modes vs doping. We found that doping carriers puts the total energy of the high-symmetry non-chiral intermediate phase lower in energy than the two chiral phases. We determined the carrier doping magnitude to overcome the chiral-achiral-transition barrier. The advantage of this finding is that we reveal the tunability of carrier doping to switch chiral-achiral transition in a real compound. Furthermore, we find significant linear Dresselhaus parameter of more than 300 meVÅ in the first valence band near the Brillouin zone center in undoped chiral SiO₂, producing Zeeman-like spin textures. Carrier doping can also tune this unique spin texture.