Metal-Insulator Transition and lattice vibrationon (DMe-DCNQI)_2Cu

(DMe-DCNQI)_2Cu 上的金属-绝缘体转变和晶格振动

• 批准号: 11440118
• 负责人: NISHIO Yutaka
• 金额: $ 6.14万
• 依托单位: Toho University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11440118/
• 关键词: Deuteration; Metal-Insulator Transition; Thermal property; Schottky Specific Heat; Organic Conductor; Tunneling Rotation; Lattice vibration; 有機導体; 金属-絶縁体; CDW; Mott転移; 秩序-無秩序転移; 有機伝導体; 分子内振動

Metal complex salts (DMe-DCNQI)_2Cu exhibits a reentrant metal-insulator transition under delicate pressure. The mixing of DCNQIπ electron and Cu 3d electron located near Fermi level generates 3dFermi face and suppresses low dimensional instability. We carried out adeuteration of methyl group, a size of which can control the electronic dimensionality and tune the reentrant M-I transition.We have experimentally studied the mechanism of reentrant metal-insulator-metal transition of DCNQI-Cu system using this deuterated system. Measurements of specific heat and latent heat were carried out by thermal relaxation (0.5<T<40K), adiabatic pulse (20<T<100K) and Differential Thermal Analysis (DTA) methods on samples under various chemical pressures. From the experimental results, we determined the Gibbs free energy difference between metallic and insulating phases and succeeded to draw the phase diagram that reproduces the experimental result quite well. We conclude that the free energy change of free electrons (metallic phase) to localized electrons with spin 1/2 (insulating phase) is essential to drive the anomalous phase transition in this system. Contribution of lattice system is also clarified.In this deuterated system, we have discovered that an orientation freedom in a deuterated methyl group brings two kinds of anomalous specific heat todeuterated (DMe-DCNQI)_2Cu system. In system containing methyl groups with one deuterium atom (CH_2D), we found Schottky type of specific heat. In system with CHD_2, we observed peaks not of Schottky type. To find out an origin and mechanism of these anomalies, we carried out the thermal study of the mixed crystals composed ofCH_2D and CHD_2. We clarified the conformational ordering of CHD_2 molecular along c axis in the DCNQI-Cu system.

金属络合物盐（DMe-DCNQI）_2Cu在微压下表现出金属-绝缘体的凹型转变。DCNQIπ电子与Cu 3d电子在费米能级附近的混合产生3d费米面，抑制了低维不稳定性.我们对DCNQI-Cu体系进行了氘代甲基的研究，利用氘代甲基的大小可以控制DCNQI-Cu体系的电子维数，并对DCNQI-Cu体系的金属-绝缘体-金属的重入跃迁机制进行了实验研究。用热弛豫法（0.5<T<40 K）、绝热脉冲法（20<T<100 K）和差热分析法（DTA）对不同化学压强下的样品进行了比热和潜热的测量。根据实验结果，我们确定了金属相和绝缘相之间的吉布斯自由能差，并成功地绘制了相图，很好地再现了实验结果。我们的结论是，自由电子（金属相）的自由能变化的本地化电子自旋1/2（绝缘相）是必不可少的驱动在这个系统中的异常相变。在这个氘代体系中，我们发现氘代甲基的取向自由给氘代（DMe-DCNQI）_2Cu体系带来了两种反常比热。在含甲基和一个氘原子（CH_2D）的体系中，发现了Schottky型比热。在CHD_2体系中，我们观察到了非肖特基型的峰。为了探讨这些异常的成因和机制，我们对CH_2D和CHD_2的混晶进行了热研究。阐明了CHD_2分子在DCNQI-Cu体系中沿沿着c轴的构象顺序。

项目成果

H. Mori, T. Okano, S. Tanaka, M. Tamura, Y.Nishio, K. Kajita and T. Mori: "Discontinuous Change of MetalInaulator Transition in the Alloyed q-system : θ-(BEDT-TTF)_2(Rb_<1-x>, Cs_x)Zn(SCN)_4"J. Phys. Soc. Jpn. 69. 1751 (2000)

H. Mori、T. Okano、S. Tanaka、M. Tamura、Y.Nishio、K. Kajita 和 T. Mori：“合金 q 系统中 MetalInaulator 转变的不连续变化：θ-(BEDT-TTF)_2( Rb_<1-x>, Cs_x)Zn(SCN)_4"J. Phys. Soc. Jpn. 69. 1751 (2000)

N. Tajima, A.Ebina-Tajima, M. Tamura, Y. Nishio, K. Kajita: "Transport Properties of Organic Conductor α- (BEDT-TTF)_2I_3 θ-(BEDT-TTF)_2I_3 Under Hydorstatic Pressure or Uniaxial Strain"Synthetic Metals. (in press).

N. Tajima、A.Ebina-Tajima、M. Tamura、Y. Nishio、K. Kajita：“有机导体 α- (BEDT-TTF)_2I_3 θ-(BEDT-TTF)_2I_3 在静水压或单轴应变下的输运特性“合成金属。（正在出版）。

Y.Nishio: "Specific heat and metal-insulator transition of (BEDT-TTF)2MZn(SCN)4 (M=Cs,Rb)"Synthetic Metals. 103(1-3). 1907-1908 (1999)

Y.Nishio：“(BEDT-TTF)2MZn(SCN)4 (M=Cs,Rb) 的比热和金属-绝缘体转变”合成金属。

T. Ichikawa, S. Kasahara, M. Tamura, Y. Nishio and K. Kajita: "Vortex Motion in an Organic Superconductor κ-(BEDT-TTF)_2Cu(SCN)_2"Synth. Metals. 103. 1822-3 (1999)

T. Ichikawa、S. Kasahara、M. Tamura、Y. Nishio 和 K. Kajita：“有机超导体 κ-(BEDT-TTF)_2Cu(SCN)_2 中的涡流运动”合成金属。 1999）

N.Tajima: "Finding of a new organic semiconductor with an extremely narrow gap"Synthetic Metals. 103(1-3). 1958-1959 (1999)

N.Tajima：“发现一种具有极窄间隙的新型有机半导体”合成金属。