Thermal Study of Reentrant Metal-Insulator Transition of DCNQI-Cu System

DCNQI-Cu体系重入金属-绝缘体转变的热研究

基本信息

批准号：
07454087
负责人：
NISHIO Yutaka
金额：
$ 4.48万
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：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07454087/
关键词：
Specific Heat Latent Heat CDW AntiferroMagnetism M-I Transition Phase Transition Deuteration Methyl Rotation DCNQI エントロピー

项目摘要

Under hydrostatic pressure of effective pressure introduced by deuteration of DCNQI molecules, (DMe-DCNQI)_2Cu system exhibits the reentrant metal-insulator transition (metal-insulator-metal) accompanied by three fold lattice distortion. In this system, not only electrical properties but also magnetic properties drastically change across the transition. We have been studying the specific heat and latent heat on samples, in which "chemical pressure" can be precisely controlled by using selectively deuterated (DMe-DCNQI)_2Cu in the temperature region (0.5K<T<100K) using the thermal, pulse and DTA methods.We have succeeded in precisely determining temperature dependence of entropy of the metallic and insulator states by the these experimental results in the vicinity of the higher temperature and lower temperature M-I transitions. In the insulator phase, electrons are localized and there is no gammaT contribution to the specific heat and entropy. On the other hand, there appears the freedom of Cu^<2+> spin. This spin system undergoes the antiferromagnetic phase transition at 6.8K.The entropy due to the spin system obtained by integrating the specific heat. It grows in the temperature range of 2-20K.Above 20K the spin system becomes completely random and entropy due to this freedom take a constant value. The entropy of the spin system in the insulator phase and the latent heat at the transition gives the information of the entropy of electron system in the metallic phase. We can calculate the free-energy of the electronic system in both phases and reconstruct the mysterious and complicated phase diagram of DMe-Cu system. We clarified that the competition between these gammaT contribution in metallic phase and freedom of Cu^<2+> spins in insulator phase drives the reentrant M-I transition.

在DCNQI分子氘化引入的有效压力的静水压力下，(DMe-DCNQI)_2Cu体系表现出伴随三倍晶格畸变的重入金属-绝缘体转变（金属-绝缘体-金属）。在这个系统中，不仅电特性而且磁特性在转变过程中都会发生巨大变化。我们一直在研究样品的比热和潜热，其中使用热、脉冲在温度范围（0.5K<T<100K）内使用选择性氘化（DMe-DCNQI）_2Cu可以精确控制“化学压力”通过高温和低温M-I转变附近的这些实验结果，我们成功地精确确定了金属态和绝缘体态熵的温度依赖性。在绝缘体相中，电子被局域化，并且伽玛T对比热和熵没有贡献。另一方面，出现了Cu^<2+>自旋的自由度。该自旋系统在 6.8K 时发生反铁磁相变。通过积分比热获得自旋系统产生的熵。它在2-20K的温度范围内生长。超过20K，自旋系统变得完全随机，并且由于这种自由度，熵取恒定值。绝缘体相中自旋系统的熵和跃迁时的潜热给出了金属相中电子系统的熵的信息。我们可以计算电子系统在两个相中的自由能，并重建DMe-Cu系统神秘而复杂的相图。我们阐明了金属相中这些 gammaT 贡献与绝缘体相中 Cu^<2+> 自旋自由度之间的竞争驱动了重入 M-I 转变。