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

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。

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.