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

金属络合盐（DMe-DCNQI）_2Cu在微细压力下表现出可重入的金属绝缘体转变。DCNQIπ电子与Cu三维电子在费米能级附近的混合产生了三维费米面，抑制了低维不稳定性。我们进行了甲基的氘化，其大小可以控制电子维数并调节可重入的M-I跃迁。实验研究了DCNQI-Cu体系的金属-绝缘体-金属重入跃迁机理。采用热松弛法（0.5<T<40K）、绝热脉冲法（20<T<100K）和差热分析法（DTA）对不同化学压力下的样品进行比热和潜热的测量。根据实验结果，我们确定了金属相和绝缘相的吉布斯自由能差，并成功地绘制了与实验结果相当吻合的相图。我们得出结论，自由电子（金属相）向自旋为1/2的局域电子（绝缘相）的自由能变化是驱动该体系异常相变的必要条件。阐明了格系的贡献。在该体系中，我们发现氘化甲基的取向自由给氘化（DMe-DCNQI）_2Cu体系带来了两种异常比热。在含一个氘原子（CH_2D）的甲基体系中，发现了肖特基型比热。在含CHD_2的体系中，我们观察到的峰不是肖特基型的。为了找出这些异常的成因和机理，我们对ch_2d和CHD_2组成的混合晶体进行了热研究。我们明确了DCNQI-Cu体系中chd2分子沿c轴的构象顺序。

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.