Gupta Sunny, Kutana Alex, Yakobson Boris I
Department of Materials Science and Nanoengineering , Rice University , Houston , Texas 77005 , United States.
J Phys Chem Lett. 2018 Jun 7;9(11):2757-2762. doi: 10.1021/acs.jpclett.8b00640. Epub 2018 May 11.
Two-dimensional single-layer boron (borophene) has emerged as a new material with several intriguing properties. Recently, the β polymorph of borophene was grown on Ag(111), and observed to host Dirac fermions. Similar to graphene, β borophene can be described as atom-vacancy pseudoalloy on a closed-packed triangular lattice; however, unlike graphene, the origin of its Dirac fermions is yet unclear. Here, using first-principles calculations, we probe the origin of Dirac fermions in freestanding and Ag(111)-supported β borophene. The freestanding β sheet hosts two Dirac cones and a topologically nontrivial Dirac nodal line with interesting Dirac-like edge states. On Ag(111), the Dirac cones develop a gap, whereas the topologically protected nodal line remains intact, and its position in the Brillouin zone matches that of the Dirac-like electronic states seen in the experiment. The presence of nontrivial topological states near the Fermi level in borophene makes its electronic properties important for both fundamental and applied research.
二维单层硼（硼烯）已成为一种具有多种有趣特性的新材料。最近，硼烯的β多晶型物在Ag(111)上生长，并观察到其包含狄拉克费米子。与石墨烯类似，β硼烯可被描述为密排三角晶格上的原子空位伪合金；然而，与石墨烯不同的是，其狄拉克费米子的起源尚不清楚。在此，我们使用第一性原理计算来探究独立的和Ag(111)支撑的β硼烯中狄拉克费米子的起源。独立的β片层包含两个狄拉克锥和一条具有有趣的类狄拉克边缘态的拓扑非平凡狄拉克节线。在Ag(111)上，狄拉克锥出现能隙，而拓扑保护的节线保持完整，并且其在布里渊区中的位置与实验中观察到的类狄拉克电子态的位置相匹配。硼烯中费米能级附近存在非平凡拓扑态，这使得其电子特性对基础研究和应用研究都很重要。
