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

• 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
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07640497/
• 关键词: Organic Superconductor; Metal-Insulator transition; Specific Heat; Hubbard Gap; 電子比熱係数; Mott絶縁体; d-波超伝導

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.

本项目的目的是通过低温比热测量来阐明基于BEDT-TTF和类似分子的有机体系中电子相关的影响和金属-绝缘体转变的本质，特别是关注具有κ型晶体结构的材料。利用本项目的资金支持，提高了配备3 He制冷机和稀释制冷机的量热仪的精度，以进行实验。对绝缘材料kappa-（BEDT-TTF）<@D22@> D2 X（X=Cu [N（CN）<@D22 @>D2] Cl，d<@D28@>D2Cu [N（CN）<@D22@>D2] Br）的电子比热系数γ在（）SY ±-的偏差范围内几乎为零。在X=Cu（NCS）_2，Cu [N（CN）_2] Br的超导盐中，由准粒子激发决定的电子比热与温度的关系为二次曲线。在低于1 T的弱磁场下，两种材料的电子比热都随磁场的平方根变化迅速恢复。这一事实是一致的理解与温度依赖性的结果，在不同的性质，通常的BCS型超导体。强有力地提出了d波型超导与电子关联效应耦合的可能性。

项目成果

Y.Nakazawa, A.Kawamoto, K.Kanoda: "Characterlzation of Low-Temperature Electronic States of Organic conductors α-(BEDT-TTF)_2MHg(SCN)_4[M=K,Rb and NH_4]" Physical Review B. 52. 12890-12894 (1995)

Y.Nakazawa、A.Kawamoto、K.Kanoda：“有机导体低温电子态的表征 α-(BEDT-TTF)_2MHg(SCN)_4[M=K、Rb 和 NH_4]”物理评论 B.52 .12890-12894 (1995)

Y.Nakazawa and K.Kanoda: "Thermodynamic Property of OrganicSuperconductor k-(BEDT-TTF)_2X [X=Cu(NCS)_2,Cu[N(CN)_2]Br]" Physica C. 282-287. 1897-1898 (1997)

Y.Nakazawa 和 K.Kanoda：“有机超导体 k-(BEDT-TTF)_2X [X=Cu(NCS)_2,Cu[N(CN)_2]Br] 的热力学性质”Physica C. 282-287。

Y.Nakazawa, A.Kawamoto and K.Kanoda: "Characterization of Low-Temperature Electronic States of Organic Conductors, alpha- (BEDT-TTF) _2MHg (SCN) _4 [M=K,Rb and NH_4]" Phys.Rev.B52. 12890-12894 (1995)

Y.Nakazawa、A.Kawamoto 和 K.Kanoda：“有机导体低温电子态的表征，α- (BEDT-TTF) _2MHg (SCN) _4 [M=K、Rb 和 NH_4]”Phys.Rev。

Y.Nakazawa and K.Kanoda: "Thermodynamic Property of Organic Superconductor kappa- (BEDT-TTF) _2X [X=Cu (NCS) _2, Cu [N (CN) _2] Br]" Physica C. 282-287. 1897-1898 (1997)

Y.Nakazawa 和 K.Kanoda：“有机超导体 kappa- (BEDT-TTF) _2X [X=Cu (NCS) _2, Cu [N (CN) _2] Br] 的热力学性质”Physica C. 282-287。

Y.Nakazawa and K.Kanoda: "Low-Temperature Specific Heat Studies on Superconductors and Mott Insulators in k-(BEDT-TTF)_2X System" Synthetic Metals. 85. 1563-1564 (1997)

Y.Nakazawa 和 K.Kanoda：“k-(BEDT-TTF)_2X 系统中超导体和莫特绝缘体的低温比热研究”合成金属。