  We report the discovery of a pristine crystalline 3D carbon that is magnetic,
electrically conductive and stable under ambient conditions. This carbon
material, which has remained elusive for decades, is synthesized by using the
chemical vapor deposition (CVD) technique with a particular organic molecular
precursor 3,3-dimethyl-1-butene (C6H12). An exhaustive computational search of
the potential energy surface reveals its unique sp2-sp3 hybrid bonding
topology. Synergistic studies involving a large number of experimental
techniques and multi-scale first-principles calculations reveal the origin of
its novel properties due to the special arrangement of sp2 carbon atoms in
lattice. The discovery of this U-carbon, named such because of its unusual
structure and properties, can open a new chapter in carbon science.
