| CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES |
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Physical Origin of Color Changes in Lutetium Hydride under Pressure |
| Run Lv1,2, Wenqian Tu1,2, Dingfu Shao1, Yuping Sun1,3,4, and Wenjian Lu1* |
1Key Laboratory of Materials Physics, Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
2Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China
3High Magnetic Field Laboratory, Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
4Collaborative Innovation Center of Microstructures, Nanjing University, Nanjing 210093, China
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| Cite this article: |
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Run Lv, Wenqian Tu, Dingfu Shao et al 2023 Chin. Phys. Lett. 40 117401 |
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Abstract Recently, near-ambient superconductivity was claimed in nitrogen-doped lutetium hydride (LuH$_{3-\delta}$N$_{\rm{\varepsilon}})$. Unfortunately, all follow-up research still cannot find superconductivity signs in successfully synthesized lutetium dihydride (LuH$_{2}$) and N-doped LuH$_{2\pm x}$N$_{y}$. However, a similar intriguing observation was the pressure-induced color changes (from blue to pink and subsequent red). The physical understanding of its origin and the correlation between the color, crystal structure, and chemical composition of Lu–H–N is still lacking. In this work, we systematically investigated the optical properties of LuH$_{2}$ and LuH$_{3}$, and the effects of hydrogen vacancies and nitrogen doping using the first-principles calculations by considering both interband and intraband contributions. Our results demonstrate that the evolution of reflectivity peaks near blue and red light, which is driven by changes in the band gap and Fermi velocity of free electrons, resulting in the blue-to-red color change under pressure. In contrast, LuH$_{3}$ exhibits gray and no color change up to 50 GPa. Furthermore, we investigated the effects of hydrogen vacancies and nitrogen doping on its optical properties. Hydrogen vacancies can significantly decrease the pressure of blue-to-red color change in LuH$_{2}$ but do not have a noticeable effect on the color of LuH$_{3}$. The N-doped LuH$_{2}$ with the substitution of a hydrogen atom at the tetrahedral position maintains the color change when the N-doping concentration is low. As the doping level increases, this trend becomes less obvious, while other N-doped structures do not show a blue-to-red color change. Our results can clarify the origin of the experimental observed blue-to-red color change in lutetium hydride and also provide a further understanding of the potential N-doped lutetium dihydride.
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Received: 19 July 2023
Published: 13 November 2023
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| PACS: |
74.70.-b
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(Superconducting materials other than cuprates)
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78.40.-q
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(Absorption and reflection spectra: visible and ultraviolet)
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