Superconductivity Above 100 K Predicted in Carbon-Cage Network.

To explore carbide superconductors with higher transition temperature, two novel carbon structures of cage-network are designed and their superconductivity is studied by doping metals. MC6 and MC10 are respectively identified as C24 and C32 cage-network structures. This study finds that both carbon structures drive strong electron-phonon interaction and can exhibit superconductivity above liquid nitrogen temperature. Importantly, the superconducting transition temperatures above 100 K are predicted to be achieved in C24 -cage-network systems doped by Na, Mg, Al, In, and Tl at ambient pressure, which is far higher than those in graphite, fullerene, and other carbides. Meanwhile, the superconductivity of cage-network carbides is also found to be sensitive to the electronegativity and concentration of dopant M. The result indicates that the higher transition temperatures can be obtained by optimizing the carbon-cage-network structures and the doping conditions. The study suggests that the carbon-cage-network structure is a direction to explore high-temperature superconducting carbides.

Metallization and superconductivity in methane doped by beryllium at low pressure.

As one of the simplest hydrocarbons, methane (CH4) has great potential in the research of superconductors. However, the metallization of CH4 has been an issue for a long time. Here, we report the structure, metallization, and superconductivity of CH4 doped by Be at low pressures, based on first-principles calculations. The result shows that the thermodynamically stable BeCH4 with P1[combining macron] space-group can transform into a metal at ambient pressure. This ternary hydride BeCH4 exhibits a superconductivity of ∼6 K below 25.6 GPa. Interestingly, the superconducting critical temperature of BeCH4 can reach ∼30 K at 80 GPa in the form of an a-P1 space-group phase. The charge transfer from Be to CH4 molecules plays an important role in the superconductivity. Our results present a novel way to realize the metallization of methane at relative pressures and indicate that the doped methane is a potential candidate for seeking high temperature and low pressure superconductivity.