Specific Heat Studies on Metal-Insulator Transition of Strongly Correlated Organic Systems

强关联有机体系金属-绝缘体转变的比热研究

基本信息

批准号：
07640497
负责人：
NAKAZAWA Yasuhiro
金额：
$ 1.34万
依托单位：
Okazaki National Research Institutes
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
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

项目摘要

The aim of this project is to clarify the effects of electron correlation and the nature of Metal-Insulator transition in organic system based on BEDT-TTF and similar molecules through low-temperature specific heat measurements, especially focusing on the materials which have kappa-type of crystal structure. Using the financial support of this project, the precision of the calorimeter equipped with the 3He refrigerator and the dilution refrigerator was improved to perform the experiments. In addition, we have also performed calorimetric calibration under several magnetic fields.For insulating material of kappa- (BEDT-TTF) <@D22@>D2X with X=Cu [N (CN) <@D22@>D2] CI,d<@D28@>D2Cu [N (CN) <@D22@>D2] Br, we have found that the electronic specific heat coefficients, gamma is almost zero within the deviation of(]SY.+-。[)0.1mJ/molK2, which demonstrates the existence of distinct charge gap structure around the Fermi level due to the correlation effect of electrons.In the superconducting salts of X=Cu (NCS) _2, Cu [N (CN) _2] Br, the electronic specific heat dominated by the quasi-particle excitations was observed as the quadratic temperature dependence. Under weak magnetic field below 1T,the electronic specific heat recovers rapidly with a square root dependence of magnetic field in both materials. This fact is consistently understood with the temperature dependence results in terms of the different nature of usual BCS type superconductors. The possibility of the d-wave type superconductivity coupled with the electron correlation effect is strongly suggested.

该项目的目的是通过低温比热测量，阐明基于BEDT-TTF和类似分子的有机系统中电子关联的影响和金属-绝缘体转变的性质，特别是关注具有kappa型的材料利用该项目的资金支持，提高了配备3He制冷机和稀释制冷机的量热仪的精度来进行实验，此外，我们还进行了多种磁场下的量热校准。的kappa- (BEDT-TTF) <@D22@>D2X，其中 X=Cu [N (CN) <@D22@>D2] CI,d<@D28@>D2Cu [N (CN) <@D22@>D2] Br，我们发现电子比热系数gamma在(]SY.+-.[)0.1mJ/molK2的偏差内几乎为零，这证明了明显的电荷间隙结构的存在在X=Cu(NCS)_2、Cu[N(CN)_2]Br超导盐中，观察到以准粒子激发为主的电子比热为在低于 1T 的弱磁场下，两种材料的电子比热均随磁场的平方根快速恢复，这一事实与不同温度依赖性结果一致。强烈暗示了通常 BCS 型超导体的性质与电子相关效应耦合的 d 波型超导性的可能性。