Silicene is a 2-D hexagonal honeycomb material with a single layer Silicon (Fig.1). On the one hand, similar honeycomb lattice structures as Graphene let it share most of the marvelous physical properties of graphene, especially the gapless Dirac fermions at the Brillouin-zone corner. On the other hand, it is the low buckled geometry that makes Silicene have some remarkable properties which Graphene doesn’t have.

Recently, the group of Prof. Yugui Yao makes some influential researches on Silicene. The existence of the Quantum spin Hall effect (QSHE) was first proposed by Kane and Mele in graphene, where SOC opens a band gap at the Dirac points. The subsequent work of Prof. Yao, however, showed that the SOC is rather weak and QSHE in graphene can occur only at unrealistically low temperature（0.01mK）. 【Phys. Rev. B 75, 041401(R) (2007)，cited 368 times】. QSHE in HgTe quantum wells and other systems have more or less serious limitations such as toxicity, difficulty in processing, and incompatibility with current silicon-based electronic technology. To find a better way，in 2011，the group of Prof. Yugui Yao predicted that QSHE could be achieved at 18K in Silicene and other systems such as Germanene and Stanene at room temperature.【Phys. Rev. Lett. 107, 076802 (2011)，cited 619 times；Phys. Rev. B 84, 195430 (2011)，cited 305 times】. Silicene is compatible with recent industry of silicon-based microelectronics, whereas other QSHE systems aren’t. Hence silicene has broad application prospects.

Fig 1 The lattice geometry of low-buckled silicene. (a),(b) The lattice geometry from the side view and top view,respectively. Note that the A sublattice (red or gray) and B sublattice (yellow or light gray) are not coplanar. (c) Definition of the angle θ as between the Si-Si bond and the z direction normal to the plane. (d) The relativistic band structure of low-buckled silicene. Inset: Zoom of the energy dispersion near the K point and the gap induced by SOC.

The theory works, the group made, interest a lot of international experimental groups including some great labs in France, Japan and China who try their best to grow Silicene and hope to find QSHE. Recently, based on their previous works, Prof. Yao and assistant Prof. C.-C. Liu in school of Physics, BIT cooperated with Prof. Kehui Wu and Sheng Meng made some researches on crystal structure and electronic properties of Silicene, and find some intriguing results. According to the extension growth of silicene on Ag surface, √3x√3 phase superstructure of Silicene was found on Ag(111). Its probably structure shown in Fig.2 was determined combining with DFT calculation. This work proved the existence of Dirac Fermion and became the basis of next research of novel quantum effects, which was published on Phys. Rev. Lett. 109, 056804 (2012).

Besides, with further theoretical calculation combining with experiments, at appropriate temperature and coverage, thin films of single layer or more layers of Silicene can be grown (Nano Lett. 12, 3507 (2012)). The properties of bilayer Silicene have been studied by Group of Prof. Yao and their collaborators, and they predicted that d+id' chiral superconductivity could be realized in this system. And with suitable strains in this system, high temperature superconductivity can be achieved (Phys. Rev. Lett. 111, 066804 (2013)). If it can be proved by experiment, a new century of modern silicon industry would come. It’s worth noticing that recent experiments showed that Silicene may be a superconductor【Appl. Phys. Lett. 102, 081602 (2013)】.

These researches were supported by grants from the National Science Foundation of China and the Ministry of Science and Technology of China.

Fig. 2 (a),(b) The top view and side view of the lattice geometry of the low-buckled silicene structure (AB) and √3x√3 superstructure (AB-A), respectively. Note that in the √3x√3 superstructure a Si atom with planar coordinate (2√3x2√3)is pulled downward. The red (black), yellow (light gray), and green (dark gray) balls represent the A, B, and -A Si atoms, respectively. (c) The structural phase transition diagram of silicene depending on the lattice constants of √3x√3 superstructure. (d) A larger schematic model illuminating the honeycomb structure of √3x√3 reconstructed silicene.

References

1. Cheng-Cheng Liu, WanXiang Feng and Yugui Yao, Phys.Rev. Lett. 107, 076802 (2011).

2. Cheng-Cheng Liu, Hua Jiang and Yugui Yao, Phys. Rev. B 84, 10195430 (2011).

3. L. Chen, Cheng-Cheng Liu, B. Feng, X. He, P. Cheng, Z. Ding, S. Meng, Yugui Yao*, K. Wu*, Phys. Rev. Lett., 109, 056804 (2012)

4. B. Feng, Z. Ding, S. Meng, Yugui Yao, X. He, P. Cheng, L. Chen, and K. Wu, Nano Lett. 12, 3507 (2012).

5. Feng Liu, Cheng-Cheng Liu, Kehui Wu, Fan Yang, Yugui Yao，Phys. Rev. Lett., 111, 066804 (2013).

Release date:2015-10-27