Dirac Cones and Nodal Line in Borophene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Two-dimensional single-layer boron (borophene) exhibits unique electronic properties.
• The β12 polymorph of borophene on Ag(111) hosts Dirac fermions, but their origin is unclear.
• Borophene shares similarities with graphene as a pseudoalloy on a triangular lattice.

Purpose of the Study:

• To investigate the origin of Dirac fermions in freestanding and Ag(111)-supported β12 borophene.
• To understand the topological properties of β12 borophene.
• To correlate theoretical findings with experimental observations.

Main Methods:

• First-principles calculations were employed.
• Electronic band structures were analyzed for freestanding and supported β12 borophene.
• Topological properties and electronic states were examined.

Main Results:

• Freestanding β12 borophene exhibits two Dirac cones and a topologically nontrivial Dirac nodal line with edge states.
• On Ag(111), Dirac cones in β12 borophene become gapped.
• The topologically protected nodal line remains intact on Ag(111), aligning with experimental Dirac-like electronic states.

Conclusions:

• The study elucidates the origin of Dirac fermions in β12 borophene.
• Topologically nontrivial states near the Fermi level are present in borophene.
• These findings are significant for fundamental research and potential applications of borophene.