2022 Fiscal Year Annual Research Report
Simultaneous optimization of crystal and magnetic structures: Applications to topological magnetic electrides
| Project/Area Number |
22J23068
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| Allocation Type | Single-year Grants |
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| Research Institution | The University of Tokyo |
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Principal Investigator |
YU Tonghua 東京大学, 工学系研究科, 特別研究員(DC1)
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| Project Period (FY) |
2022-04-22 – 2025-03-31
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| Keywords | Electrides / Topological materials / Magnetism / Molecular crystals / Ab initio calculations |
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| Outline of Annual Research Achievements |
1. We studied the electride phase in molecular crystals. By means of first-principles calculations, we showed that nontrivial electronic topology may be realized even in quasi-zero-dimensional molecular crystals, with the aid of interstitial electrons. We explicitly demonstrated the novel properties of such topological molecular crystals, such as multiple cleavable surfaces, moderately strong response to mechanical perturbations, and high-quality thermoelectricity. This work connects electrides with molecular crystals, and highlights the active role of interstitial electrons in electronic topology.
2. We expanded the boundary of electrides to include transition metal compounds. Transition metals, like manganese, iron, cobalt, and nickel, are traditionally not considered as good cation candidates in electrides, on account of their nonstandard valence. However, we showed that the interstitial orbitals could be stabilized due to the correlation effects on transition metal 3d orbitals. We found that such transition metal electrides manifest a high work function, suggestive of their stability compared to conventional electrides. Through this study we can see the interplay between electron correlation and electride phases.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
Our research initially aimed to develop a method for ab initio optimization of magnetic structures in magnetic electrides. However, we found that this method is highly computationally demanding due to the existence of non-collinear magnetic ordering. Therefore, we adjusted our research direction and instead focused on exploring the topological and magnetic properties of electride systems.
We discovered that electrides are an exciting system to investigate through our research. We expanded the scope of electrides to include molecular crystals and found that interstitial electrons can turn these crystals into topological insulators. This novel combination of topological electrides and molecular materials produces unique and noteworthy features. We also studied magnetic electrides for correlated transition metal compounds, which has not been explored before in electride materials. Our results show that transition metal cations can stabilize excess electrons at vacancy sites, resulting in a high work function.
Although we shifted our focus, our research has yielded useful results that have been published or presented. Our findings broaden the understanding of electrides and contribute to the development of new materials with unique properties.
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| Strategy for Future Research Activity |
Our research will continue be centered on electrides and will explore more about their topological and magnetic properties. Specifically, one direction could be to investigate the potential application of topological electrides in catalysis, as previous studies have shown that both the robust topological surface states and interstitial electrons in electrides can enhance catalytic activities; their unification would be of interest. In addtion, we will address the correlation effects within interstitial electrons by utilizing state-of-the-art methods, such as dynamical mean field theory. We hope to implement electrides as a fertile arena for diverse theories and methods, and meanwhile to advance our fundamental understanding of the unique properties of electrides.
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