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Acoustic Phonon Properties of (BEDT-TTF) -based organic superconductors

(BEDT-TTF)基有机超导体的声学声子特性

基本信息

批准号：
08454087
负责人：
YOSHIZAWA Masahito
金额：
$ 4.54万
依托单位：
Iwate University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08454087/
关键词：
organic superconductor organic conductor superconductivity vortex state ultrasonic measurements single crystal growth thermal conductivity thin films MBE

项目摘要

1.Vortex state in kappa- (BEDT-TTF) _2Cu (NCS) _2The vortex state of the organic superconductor kappa- (BEDT-TTF) _2Cu (NCS) _2 been investigated by ultrasonic measurements. The field dependence in the longitudinal sound velocity shows a remarkable dip. The amount to the dip is proportional to cosrheta, where rheta is the angle between the propagation direction of the sound and the magnetic field. The sound velocity anomaly is interpreted by the thermal fluctuation of the Josephson coupling between the superconducting layrs. Such anomaly is caused by a large Gruneisen parameter of this salt.2.Elastic anomaly at the superconducting transition in beta- (BEDT-TTF) _2I_3It has been known that beta- (BEDT-TTF) _2I_3 shows the second superconducting transition by low-temperature annealing. The origin of two types of superconductivity in this salt has not been made clear, so far. In this research project, we could observe the sound velocity anomalies at 2 K before annealing and at 6 K after annealing. The sound velocity anomalies could be interpreted in the frame of the thermodynamic relation.3.Large single crystal growth of organic superconductorsThe mechanism of crystal growth of (BEDT-TTF) _2I_3 has been investigated by the equilibrium analysis of polymorphic behavior in monochlorobenzene. Our study clearly indicates that (BEDT-TTF) _2I_3 crystals are decomposed to neutral BEDT-TTF and I_2 in the solvent, and that they are in the equilibrium state. It was found that alpha- (BEDT-TTF) _2I_3 is stabler that beta-salt at room temperature. However, beta-salt becomes stabler than alpha-salt at lower temperatures. This fact makes us to control tha polymorph of this salt by the solubility and the growth temperature. We could successfully grow large single crystals of alpha- (BEDT-TTF) _2I_3, beta- (BEDT-TTF) _2I_3, kappa- (BEDT-TTF) _2Cu (NCS) _2 and kappa- (BEDT-TTF) _2Cu [N (CN) _2] Br.

1.kappa- (BEDT-TTF) _2Cu (NCS) _2中的涡旋态通过超声波测量研究了有机超导体kappa- (BEDT-TTF) _2Cu (NCS) _2的涡旋态。纵向声速的场依赖性显示出显着的下降。倾角的大小与 cosrheta 成正比，其中 rheta 是声音传播方向与磁场之间的角度。声速异常是通过超导层之间约瑟夫森耦合的热波动来解释的。这种异常是由该盐的格鲁尼森参数较大引起的。2.β-(BEDT-TTF)_2I_3超导转变处的弹性异常已知β-(BEDT-TTF)_2I_3通过低温退火表现出第二次超导转变。迄今为止，这种盐中两种超导性的起源尚未明确。在本研究项目中，我们可以观察到退火前2K和退火后6K处的声速异常。声速异常可以在热力学关系的框架下解释。3.有机超导体大单晶生长通过一氯苯中多晶型行为的平衡分析研究了(BEDT-TTF)_2I_3晶体生长的机理。我们的研究清楚地表明(BEDT-TTF)_2I_3晶体在溶剂中分解为中性BEDT-TTF和I_2，并且它们处于平衡状态。结果发现，α-(BEDT-TTF)_2I_3 在室温下比 β-盐更稳定。然而，在较低温度下，β-盐比α-盐更稳定。这一事实使我们能够通过溶解度和生长温度来控制该盐的多晶型物。我们可以成功生长α-(BEDT-TTF)_2I_3、β-(BEDT-TTF)_2I_3、kappa-(BEDT-TTF)_2Cu(NCS)_2和kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br的大单晶。