Discovery of 2D Anisotropic Dirac Cones

Abstract

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.

2D Boron Sheets: Structure, Growth, and Electronic and Thermal Transport Properties

“…Dirac cones are predicted to exist in β 12 , χ 3 and fully hydrogenated δ 6 borophene (borophane) sheets. The Angle‐resolved photoemission spectroscopy (APRES) confirms the existence of gapless Dirac cones in the β 12 and χ 3 sheets of borophene on Ag(111) . Besides, the strong electron–phonon coupling resulted in phonon‐mediated superconductivity …”

“…Besides β 12 phase of borophene on Ag(111) surface, χ 3 phase is another 2D boron sheet that can be obtained on Ag(111), which has unique morphology and large area. Similar to the investigations on β 12 sheet, Feng et al also performed the ARPES measurements and first‐principle calculations to explore the electronic structures of χ 3 phase of borophene on Ag(111) . The Dirac‐cone‐like band structures are also found in the BZ of χ 3 sheet.…”

“…The borophene on substrate may also present semimetal band structures . Besides, Dirac cones may exist in borophene even it is placed on metal substrate, like β 12 ‐sheet on the Ag(111) surface …”

“…However, two pioneering groups parallelly synthesized 2D boron sheets on Ag(111), and indicated the metallic behavior of borophene with different atomic structures by scanning tunneling spectroscopy (STS) . Particularly, the extraordinary electronic structures such as Dirac cones have been found in 2D boron sheet on Ag(111) surface, i.e., the β 12 and χ 3 phases of borophene . Because of the supporting by Ag (111) surface, β 12 and χ 3 are different from the free‐standing lowest‐energy structure (α 1 /β 1 , or pmmn/pmmm).…”

“…Following the successful growth of 2D boron sheet on Ag(111) with high quality and large area through the evaporation of boron atoms to substrate with accurate substrate temperature, a series of comprehensive studies on the borophene with β 12 and χ 3 phases were performed by Feng et al First, based on tight‐binding and DFT calculations, they found the β 12 sheet can be decomposed into two triangular sublattices . The similar situation as the honeycomb lattice indicates that the Dirac cones should be found in the Brillouin zone (BZ) of β 12 sheet.…”