Electric Field Tunable Spin-Flip Scattering in Dilute Fluorinated Bilayer Graphene

In earlier work, we showed that a dilute coverage of fluorine adatoms covalently bonded to single-layer graphene leads to intriguing and striking phenomena including metal-insulator transition, very large negative magneto-resistance and enhanced spin-flip scattering. By fluorinating only the top layer of a bilayer graphene sheet, this work investigates the possibility of tuning the spin-flip scattering rate $in$ $situ$ via a perpendicular electric field $D$. Dual HfO$_2$ gated field effect transistors of dilute fluorinated bilayer graphene (DFBG) (F:C ~ 0.03 \%) are used, in which we independently control $D$ and the carrier density $n$. The $n$-dependence of the conductance exhibits signatures of midgap state scattering. The midgap states also lead to increased conduction in the band gap of biased DFBG. Magneto-resistance measurements and weak localization analyses over a wide range of $n$, temperatures, and $D$-fields indicate the presence of spin-flip scattering, similar to what is observed in dilute fluorinated single-layer graphene. Most strikingly, the spin-flip rate can be tuned by over a factor of 2 via controlling the direction and magnitude of the $D$-field. These results demonstrate the potential of DFBG in spintronic applications.