1986 Fiscal Year Final Research Report Summary
Optical Properties of One-Dimensional Charge-Density-Wave Semiconductors under High Pressures
| Project/Area Number |
60460026
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
KURODA NORITAKA The Research Institute for Iron, Steel and Other Metals, Assoc.Prof., 金属材料研究所, 助教授 (40005963)
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| Co-Investigator(Kenkyū-buntansha) |
NISHITANI Ryusuke the same as above,Assist.Prof, 金属材料研究所, 助手 (50167566)
SASAKI Yoshiro the same as above,Assist.Prof, 金属材料研究所, 助手 (90101154)
NISHINA Yuichiro The Research Institute for Iron, Steel and Other Metals,Prof, 金属材料研究所, 教授 (90005851)
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| Project Period (FY) |
1985 – 1986
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| Keywords | Halogen-bridged Mixed-Valence Plutinum Complex / Charge Density Wave / Soliton / Diamond Anvil / 顕微分光装置 |
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| Research Abstract |
We have studied the pressure dependence of the optical absorption spectrum in quasi one-dimensional halogen-bridged <Pt^(II)> - <Pt^(IV)> complexes to clarify the role of the transfer energy between <dz^2> orbitals of Pt ions in determining the Peierls gap, and to search for the excitation of kink solitons which must be born in these doubly degenerate charge density wave systems. The hydrostatic pressure is generated by the use of the diamond anvil apparatus. Since the optical transition across the Peierls gap is allowed only for the electric field directed parallel to the -X- <Pt^(II)> -X- <Pt^(IV)> -X- chain (X = Cl,Br,I), the light source must be linearly polarized. For this purpose, we have developed the technique to seal the linear polarizer into the pressure cell together with a single crystal of the sample. This technique enables us to obtain the linearly polarized absorption spectrum at pressures up to 3 GPa, despite that the radiation is strongly depolarized by the strain of t
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he diamond anvils. The fundamental absorption edge is found to shift towards lower energies with increase in the pressure, the rate being -0.2 - -0.3 eV/GPa in all the materials examined. The rate is about an order of magnitude higher than that of the indirect absorption edge in an ordinary semiconductor. It turns out from this result that the increase in the transfer energy, that is, the kinetic energy causes to decrease the Peierls gap. This fact implies that the application of pressure increases the metallicity of a one-dimensional semiconductor quite efficiently. Besides, a midgap absorption band appears upon the onset of pressure in the Pt-Cl salt. The spectral position remains near the middle of the Peierls gap at any pressure. The absorption intensity increases as an exponential function of the shift of the spectral position. It is concluded from these findings that the states responsible for the midgap absorption band are soliton excitations similar to the kinks in polyacetylene. Less
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Research Products
(10 results)
