1997 Fiscal Year Final Research Report Summary
Study of 3-Dimensional Peierls Semiconductors and Soft Excitons
| Project/Area Number |
07454059
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | UNIVERSITY OF TSUKUBA |
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Principal Investigator |
UWE Hiromoto University of Tsukuba, Inst.of Applied Physics, Professor, 物理工学系, 教授 (10132979)
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| Project Period (FY) |
1995 – 1997
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| Keywords | Peierls transition / Metal-Semiconductor trasition / optical absorption / exciton / BaBiO_3 / Ba_<1-X>K_XBiO_3 / BaBi_<1-X>Pb_XO_3 |
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| Research Abstract |
1. We have found indirect-gap excitons in mid-infrared spectra of BaBiO_3 with principal quantum number 1 and the above. From the analysis of the spectra, the indirect band-gap energy is found to equal twice of the activation energy of the electric conductivity.
2. In BPB, with increasing Pb content, the band-gap energy is found to increase once and then decrease. This is because the band widths of Bi^<3+> and Bi^<5+> decrease but that of Pb Bi^<4+> increases with the bottom energy below that of Bi^<6+> band above a certain content of Pb.
3. In BKB, the band gap energy is found to decrease with K content to cross zero at x=O.28 with semiconductor-metal transition. In a semiconducting BKB, a mid-infrared optical window between optical phonon band and electronic band edge is found to be closed below a structural phase transition temperature because of decrease of the band-gap energy.
4. The excitation energy of excitons in BaBiO_3 is found to be ca lOOOcm Bi^<-1>. In BKB or BPB, there is a possibility of thermally excited excitons with narrow band gap energy. However, we have found increasing refractivity in mid infrared spectral region with increasing Pb content in BPB.This indicates non-decreasing excitation energy of excitons in narrowed gap BPB.
5. In BaBiO_3, we have found bilinear coupling between excitons and optical phonons. Integrated optical conductivity of optical phonons is found to decrease with increasing temperature. On the other hand, the exciton absorption intensity increases. This shows coupled vibration between optical phonons and excitons.
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