New metallic carbon: Three dimensionally carbon allotropes comprising ultrathin diamond nanostripes

Metallic carbon has received long-standing attentions for its fascinating applications in superconductivity, electronic devices and high-performance anode materials. Here we design two types of metallic carbon phases, namely O-type and T-type carbon, using self-assembling diamond nanostripes as building block and CC bond as linkers. These O-type and T-type allotropes are energetically more favorable than most previously identified three-dimensional (3D) metallic carbon allotropies, while their stability is confirmed by a series of first-principles calculations. Excitingly, these all-carbon crystals not only exhibit ultrahigh Fermi velocity and anisotropic electrical conductivity, but also belong to superhard materials with good mechanical properties. By simulating the X-ray diffraction patterns, we propose that O-type and T-type carbon would be one of the unidentified carbon phases observed in recent detonation experiments or shock-compression of tetracyanoethylene (TCE) powder. The good electrical conductivity, high mechanical strength, tunable electronic properties might find applications in electromechanical systems and nanoelectronic devices.