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Electronic States of Molecular Compounds, (DI-DCNQI)2M, (M=Li,Ag,Cu), and Doped System, (DMe-DCNQI)2Li1-xCux
https://ir.soken.ac.jp/records/290
https://ir.soken.ac.jp/records/290ad14d4e8-fd9b-472d-9b7a-2e1dad51ec3a
| 名前 / ファイル | ライセンス | アクション |
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要旨・審査要旨 / Abstract, Screening Result (393.4 kB)
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本文 / Thesis (7.3 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||||
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| 公開日 | 2010-02-22 | |||||||
| タイトル | ||||||||
| タイトル | Electronic States of Molecular Compounds, (DI-DCNQI)2M, (M=Li,Ag,Cu), and Doped System, (DMe-DCNQI)2Li1-xCux | |||||||
| タイトル | ||||||||
| タイトル | Electronic States of Molecular Compounds, (DI-DCNQI)2M, (M=Li,Ag,Cu), and Doped System, (DMe-DCNQI)2Li1-xCux | |||||||
| 言語 | en | |||||||
| 言語 | ||||||||
| 言語 | eng | |||||||
| 資源タイプ | ||||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||||
| 資源タイプ | thesis | |||||||
| 著者名 |
開, 康一
× 開, 康一
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| フリガナ |
ヒラキ, コウイチ
× ヒラキ, コウイチ
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| 著者 |
HIRAKI, Ko-ichi
× HIRAKI, Ko-ichi
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| 学位授与機関 | ||||||||
| 学位授与機関名 | 総合研究大学院大学 | |||||||
| 学位名 | ||||||||
| 学位名 | 博士（理学） | |||||||
| 学位記番号 | ||||||||
| 内容記述タイプ | Other | |||||||
| 内容記述 | 総研大甲第260号 | |||||||
| 研究科 | ||||||||
| 値 | 数物科学研究科 | |||||||
| 専攻 | ||||||||
| 値 | 08 機能分子科学専攻 | |||||||
| 学位授与年月日 | ||||||||
| 学位授与年月日 | 1997-03-24 | |||||||
| 学位授与年度 | ||||||||
| 値 | 1996 | |||||||
| 要旨 | ||||||||
| 内容記述タイプ | Other | |||||||
| 内容記述 | The Molecular compounds, (DMe-DCNQI) 2M, where DMe-DCNQI is 2, 5-dimethyl-dicyanoquinonediimine and M is Li, Ag or Cu, attract a variety of physical interests. DMe-DCNQI is a planer molecule as shown in Fig. 1(a). This is an organic π acceptor molecule, which are uniformly stacked along the crystallographical c axis, forming one dimensional (1D) columns in the compounds. The metallic ions, M, are coordinated tetrahedrally by CN groups of DMe-DCNQI molecules. The complexes with M are all isostructual with the space group, I 4 1/a, irrespectively of the M(Li, Ag, Cu). (DMe-DCNQI)2Cu(DMe-Cu) remains metallic down to low temperatures in spite of the low dimensional structure. The 3d orbitals of Cu ions hybridize with LUMO (the Lowest Unoccupied Molecular Orbitals) of DMe-DCNQI and play a role of interconnecting the 1D π band. The valence of the Cu ions are around 4/3(Cu1+Cu2+〓2:1) and the filling of 1D π band turns out to be about 1/3. On the other hand, the compound with monovalent Li/Ag (DMe-Li/DMe-Ag) has the same crystal symmetry as the DMe-Cu. The electrons of Li/Ag does not contribute to the conduction band. Therefore it behaves as a 1D electronic system with a quarter filled π band. The DMe-Li/DMe-Ag is metallic in high temperature region, while it undergoes a non-magnetic(spin-) Peierls transition with freezing of 2kF charge density wave(CDW). DI-DCNQI molecule is shown in Fig. 1(b), where methyl group in DMe-DCNQI is replaced by iodine. Recently, the electronic state of Cu salt of DI-DCNQI, DI-Cu, has been reported. The possibility of the high correlation effect of DI-Cu was suggested by the measurements of resistivity, spin susceptibility and band calculation. This peculiarities in DI-Cu is attributed to degree of hybridization and intra/inter-column transfer integrals different from those of DMe-DCNQI system. In the present study, the novel electronic states of DCNQI-M system have been searched for by 1) substituting Me by I, and 2) controlling the filling of the 1D π band of DMe-DCNQI columns through the Cu doping to the DMe-Li. The Cu doping is expected to cause some change in filling of the band and generate 3D nature through hybridization of the Cu 3d orbitals with the π band. The electronic states were investigated by the resistivity, ρ, spin susceptibility, χ and 1H- and 13C-NMR measurements. The cyano carbons in the DCNQI molecules are enriched by 13C isotope for NMR. 1. Electronic state of (DI-DCNQI)2M (DI-DCNQI)2Ag DI-Ag is insulating below room temperature with a charge gap of ～490K, which was obtained by the temperature dependence of ρ. The χ follows a Curie-Wei β law in high temperature region and forms a broad peak around 35K. At higher temperatures above 20OK, 13C-NMR spectra are single lines because all of 13C sites are crystallographically equivalent. Below 200K, however, the spectra get split into two lines with different shifts and width. Since the shift is proportional to the local electron density of LUMO at the 13C site. This line separation in the paramagnetic state indicates disproportionation of electron density. This result is an evidence of 4kF CDW with the two fold charge modulation along the c axis. It is emphasized that the CDW in this system is the charge modulation type rather than the lattice modulation type, which is widely observed in many organic systems with quarter filled band. The 4kF CDW leads a quarter filling in electronic band to a half filling. Thus, the insulating state of DI-Ag is understood as Mott insulator by the large Coulomb repulsion, U. At 5.5 K, 1H-NMR relaxation rate, 1T1-1, forms a peak anomaly and the spectral width abruptly become broadened as shown in Fig. 2. These evidence an antiferromagnetic ordering of the spins at this temperature. The ground state of the Ag salt of DI-DCNQI is antiferromagnetic. The DI-Ag is considered as a nearly pure π electron system like the DMe-Ag. The magnetism of the DI-Ag is sharp contrast to the non magnetic groundstate in the DMe-Ag. The DI-Ag is the first case in the DCNQI-M system that them electrons are responsible for antiferromagnetic ground state. The difference of the ground states between the two systems are attributable to the difference of the dimensionality of the electronic states. In fact, from estimation of the transfer integral by the band calculation, the DI-system is known to be more three-dimensional than the DMe-system. (DI-DCNQI)2Cu The DI-Cu remains metallic down to low temperatures as DMe-Cu does. There is no sign of 4kv CDW in NMR spectra, which remains single line in whole temperature range. In Fig. 3, the spectral shift of 13C- and 1H-NMR, 13K(square)and 1K(circle) from the line position of neutral DI-DCNQI molecule is shown in comparison with χ (cross). Both of 13K and 1K form broad peaks like χ. However, it should be noted that the peak temperature of 1K is lower than that of χ while the peak temperature of 13K is slightly higher than that. The overall temperature dependence of χ is in between the two profiles. Since K probes the local spin susceptibility, this fact is considered as a microscopic evidence that the electronic structure consists of several bands with different characters, which is believed to come from hybridization of the π and d orbitals, 1H-NMR detects the electrons of π-band preferentially, while 13C-NMR at the cyano group coordinated to the Cu ions can probe the d-electrons through the off-site core polarization as well as the π electrons. 2. Carrier Doping to (DMe-DCNQI)2Li From the resistivity measurements of several alloy systems with different Cu contents, it was found that the systems up to x～30% undergo the metal-insulator transition at low temperatures while the systems with x>50% are metallic in the whole temperature range investigated. Figure 4 shows the temperature dependence of χ for typical alloy systems. A systematic change of behavior with the doping content is observed. The 13C (in the cyano group) nuclear spin-lattice relaxation rate, 13T1-1, is shown in Fig. 5. For x<30%, one can see abrupt decrease of (13T1T)-1, which is associated with the spin-Peierls transition. The transition temperature slightly shifts with increasing x. For the Cu-rich systems with x>50%, (13T1T)-1 does not exhibit any anomaly but converges into about 0.03 sec-1K-1 in the low-temperature limit. They show positive temperature dependence which have a clear correlation with the doping content. This is an indication that the doping causes some change in the electronic states, particularly in excitation spectrum visualized in higher temperature region. |
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| 値 | 有 | |||||||
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| 内容記述タイプ | Other | |||||||
| 内容記述 | application/pdf | |||||||
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| 出版タイプ | AM | |||||||
| 出版タイプResource | http://purl.org/coar/version/c_ab4af688f83e57aa | |||||||
