2016 Fiscal Year Annual Research Report
２次元物質ゲルマネンの実デバイス環境下における電子状態・輸送特性の理論研究
| Project/Area Number |
16J10944
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| Research Institution | The University of Tokyo |
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Principal Investigator |
NI ZEYUAN 東京大学, 大学院工学系研究科(工学部), 特別研究員(DC2)
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| Project Period (FY) |
2016-04-22 – 2018-03-31
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| Keywords | 2D material / substrate / topological insulator / DFT |
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| Outline of Annual Research Achievements |
Suitable substrates are necessary to protect the Dirac cone and even the topological states of germanene and stanene. Previously, we have found that group-III monochalcogenides MX can serve as suitable 2D substrates for germanene. (Phys. Chem. Chem. Phys., 17, 19039 (2015)) Further work is done in the following two directions as written in my research proposal:
1.Broad investigation of the interaction between germanene/stanene and other 2D materials is done by using data mining and DFT. We use data mining to filter out suitable 2D substrates from more than 185,000 entries in database. Then we find that germanene and stanene can preserve Diacr-cone and open a band gap on suitable substrates. The topological state of germanene and stanene are also affected by the substrates.
2.Deeper investigation of the physics in the interaction between germanene/stanene and substrate is done by using model analysis. In order to explain the different behavior of germanene and stanene on substrates, a low-energy tight binding (TB) hamiltonian of free-standing germanene under external field is used and fitted to DFT results obtained previously. Interestingly, we have found that the effect of suitable substrates can be described as a pseudoelectric field (just like electric field). Furthermore, the linear relationship between the effective mass and band gap in germanene can also be well explained.
The above work has been submitted to Physical Review B and is undergoing peer review.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The two main purpose of the last year have been well accomplished: (1) Find more suitable substrates for germanene, and even expanded to stanene; (2) Explain physically the behavior of germanene and stanene on those substrates. The results are gathered and submitted to Physical Review B. We expect our research to provide important information for experimentalists to fabricate high performance germanene and stanene devices for potential microelectronics applications.
Moreover, our study about 2D materials is extending to other novel 2D materials, like WTe2. WTe2 has many exotic properties, like large non-saturating magnetoresistance and type-II Weyl-cone. Nevertheless, its surface relaxation and thin-layer behaviors are yet to be investigated. We will seek cooperation with experimentalists.
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| Strategy for Future Research Activity |
First, germanene and stanene shall be protected by capping layers in practice. With the suitable layered substrates found previously, we can now study the behavior of germanene and stanene sandwiched between those 2D layers by using density functional theory (DFT). The combined effect of two capping layers can further tune the electronic and topological structure of germanene and stanene, which may lead to the model of practical germanene/stanene devices like field effect transistors.
Second, we will cooperate with experimental group to try to reveal the exotic property of WTe2. The surface relaxation of WTe2 will be investigated by using low-energy electron diffraction and cross-validated by DFT simulations. The impact of surface relaxation on its properties will also be revealed by DFT.
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