Discovery of 2D Anisotropic Dirac Cones.

2D anisotropic Dirac cones are observed in χ borophene, a monolayer boron sheet, using high-resolution angle-resolved photoemission spectroscopy. The Dirac cones are centered at the X and X' points. The data also reveal that the hybridization between borophene and Ag(111) is very weak, which explains the preservation of the Dirac cones. As χ borophene has been predicated to be a superconductor, the results may stimulate further research interest in the novel physics of borophene, such as the interplay between Cooper pairs and the massless Dirac fermions.