Superconducting Single-Layer T-Graphene and Novel Synthesis Routes

Single-layer superconductors are ideal materials for fabricating superconducting nano devices. However, up to date, very few single-layer elemental superconductors have been predicted and especially no one has been successfully synthesized yet. Here, using crystal structure search techniques and ab initio calculations, we predict that a single-layer planar carbon sheet with 4- and 8-membered rings called T-graphene is a new intrinsic elemental superconductor with superconducting critical temperature (T_\rm c) up to around 20.8 K. More importantly, we propose a synthesis route to obtain such a single-layer T-graphene, that is, a T-graphene potassium intercalation compound (C_4K with P4/mmm symmetry) is firstly synthesized at high pressure (>11.5 GPa) and then quenched to ambient condition; and finally, the single-layer T-graphene can be either exfoliated using the electrochemical method from the bulk C_4K, or peeled off from bulk T-graphite C_4, where C_4 can be obtained from C_4K by evaporating the K atoms. Interestingly, we find that the calculated T_\rm c of C_4K is about 30.4 K at 0 GPa, which sets a new record for layered carbon-based superconductors. The present findings add a new class of carbon-based superconductors. In particular, once the single-layer T-graphene is synthesized, it can pave the way for fabricating superconducting devices together with other 2D materials using the layer-by-layer growth techniques.