Silicene, analogous to graphene, is a one-atom-thick two-dimensional crystal of silicon which is expected to share many of the remarkable properties of graphene. The buckled honeycomb structure of silicene, along with its enhanced spin-orbit coupling, endows silicene with considerable advantages over graphene in that the spin-split states in silicene are tunable with external fields. Although the low-energy Dirac cone states lie at the heart of all novel quantum phenomena in a pristine sheet of silicene, the question of whether or not these key states can survive when silicene is grown or supported on a substrate remains hotly debated.
The high-resolution angle-resolved photoemission study on monolayer (3x3) silicene grown on Ag(111) substrate, performed by Prof. ZHOU Xingjiang’s group in the Institute of Physics, Chinese Academy of Sciences, provide key insights on this important issue. They observed a new form of Dirac cones in (3x3) silicene/Ag(111) system: the presence of six pairs of Dirac cones on the edges of the first Brillouin zone of Ag(111), other than six Dirac cones at the K points of the primary silicene(1x1) Brillouin zone that is expected for a pristine silicene.
The results show clearly that the unusual Dirac cone structure originates neither from the pristine silicene nor from the Ag(111) substrate, but from the interaction of silicene (3x3) and the Ag(111) substrate. The study provides first direct evidence on the existence of a new form of Dirac cones in silicene/Ag(111) system; it has resolved the controversy on whether Dirac cones exist in the silicene/Ag(1111) system. It also identifies the first case of a new type of Dirac Cone generated through the interaction of two different constituents. The observation of Dirac cones in silicene/Ag(111) opens a new materials platform for investigating unusual quantum phenomena and novel applications based on two-dimensional silicon systems.
This study entitled “Direct Evidence of Interaction-Induced Dirac Cones in Monolayer Silicene/Ag(111) System” was published in PNAS 113 (51)，14656-14661 （2016）.
The study was supported by the National Natural Science Foundation, the Ministry of Science and Technology of China, and the Chinese Academy of Sciences.