Optical spin injection in graphane and fluorographene

Abstract

We theoretically investigate the optical spin-injection response in different stoichiometric configurations of graphane and fluorographene using density functional theory. Our goal is to determine which configuration yields the strongest degree of spin polarization. The results show that the fluorographene zigzag configuration yields the best degree of spin polarization response (${\cal DSP}^{\mathrm{z}}$), with 98\% spin polarized electrons at the band edge and over a wide range of excitation photon energies. In contrast, other graphane and fluorographene configurations achieve a ${\cal DSP}^{\mathrm{z}}$ of roughly 83--100\%, but only within a limited photon-excitation energy range. In structures with low spin-orbit coupling, the degree of spin polarization is close to 100\% over a wide range of photon energies. For higher spin-orbit coupling, this strong response appears, but only in a narrow photon energy region. Additionally, under the band-resolved decomposition scheme, the contributions of different band-to-band transitions to the ${\cal DSP}^{\mathrm{z}}$ spectrum are identified by summing only the selected valence and conduction bands. Our findings show that almost the entire ${\cal DSP}^{\mathrm{z}}$ spectrum of the fluorographene zigzag configuration comes from transitions that involve only the top valence band, which is a mixture of C--p and F--p states.