Insulator-Metal Transition and Elastic anomalies of ET organic conductors.

ET 有机导体的绝缘体-金属转变和弹性异常。

• 批准号: 13640344
• 负责人: YOSHIZAWA Masahito
• 金额: $ 2.24万
• 依托单位: Iwate Universtiy
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640344/
• 关键词: organic conductor; layered manganite; filled skutterudite compound; ultrasonic measurements; elastic constant; superconductivity; metal-insulator transition; giant magnetoresistance

The purpose of this project is to investigate the origin of Insulator-to-Metal (IM) crossover in BEDT-TTF (ET) organic conductors by means of ultrasonic measurements. Through this project, we developed a new ultrasonic apparatus with GM-type cryocooler, which enables us to measure sound velocity, ultrasonic attenuation and resistivity automatically in the temperature range between 5 K and room temperature. In this project, we have performed the investigations on IM transition of manganites and skutterudite compounds as relating materials, together with ET organic conductors. The results are summarized as follows.(1) Elastic anomalies of k-(ET)_2Cu[N(CN)_2]Br We measured longitudinal elastic sonstants C_<11> and C_<33> of κ-(ET)_2Cu[N(CN)_2]Br, which shows the IM cross over behavior at around 100K. Both C_<11> and C_<44> show remarkable elastic softening at around 40 K. These anomalies are not affected by the application of the magnetic field. It has been predicted by the theory that th … More is IM behavior is related to the superconductivity of this system. The superconductivity is much affected by the magnetic field. These results suggest weak correlation between IM crossover behavior and superconductivity. We have investigated the coupling between vortices and elastic strain.(2) Elastic anomalies associated with Insulator-Metal transition in Manganites We have investigate layered Manganite La_<2-2%>Sr_<1+2%>Mn_2O_7 as a function of Sr concentration. We focused our attention on the 3d electronic state of Mn, when we change hole concentration. We have estimated it by using band width, crystalline electric field scheme and overlap integral, which are evaluated based on a suitable model. In addition, we have carried out the elastic constant measurements of (La_<1-Z>Pr_Z)_<1.2>Sr_<1.8>Mn_2O_7. This system shows Insulator-to-metal transition at 4.2 K in the magnetic field of 7 T. We found that the longitudinal elastic constant s***s a remarkable softening acoompanied with IM transition, and shows a hardening in higher fields. This behavior is quite different from ET system. These systematic investigation on various systems is expected to give important information on the origin of IM transition of ET system.(3) Elastic anomalies in Filled skutterudite compounds Filled skutterudite compounds, which are described by ReTr_4X_<12> (Re : Rare earth element, Tr : Transition metal, X : Pnictgen) have been investigated by ultrasonic methods. The elastic constants of LaFe_4P_<12>, PrFe_4P_<12>, NdFe_4P_<12>, LaRu_4Sb_<12>, CeRu_4Sb_<12> and PrRu_4Sb_<12> have been measured, so far. The elastic softening of (C_<11>-C_<12>)/2 has been found in PrFe_4P_<12>. This confirms that the 4f ground state of this system is G_3. The peculiar field dependence of the elastic constant clearly shows the evidence of quadrupolar Kondo effect, ant that this effect is much affected by the magnetic field. Less

本项目的目的是通过超声测量来研究BEDT-TTF(ET)有机导体中绝缘体-金属(IM)交叉的来源。通过本项目，我们研制了一种新型的带有GM型制冷机的超声仪，使我们能够在5K到室温的温度范围内自动测量声速、超声衰减和电阻率。在本项目中，我们以锰氧化物和方锰矿化合物为相关材料，与Et有机导体一起进行了IM相变的研究。结果如下：(1)k-(Et)_2Cu[N(CN)_2]BR的弹性反常我们测量了κ-(Et)_2Cu[N(CN)_2]BR的纵向弹性应力C_&lt；11&gt；和C_&lt；33&gt；，它们在100K左右表现出IM交叉行为。在40K左右，C&lt；11&gt；和C&lt；44&gt；都表现出明显的弹性软化，这些异常不受外加磁场的影响。理论上已经预测到…更重要的是，IM行为与该体系的超导电性有关。超导电性受磁场的影响很大。这些结果表明IM交叉行为与超导电性之间的相关性很弱。(2)与绝缘体-金属转变有关的弹性反常我们研究了层状锰氧化物La_&lt；2-2%&gt；sr_&lt；1+2%&gt；Mn_2O_7随锶浓度的变化。当我们改变空穴浓度时，我们将注意力集中在了Mn的3D电子态上。我们用带宽、晶态电场方案和重叠积分对其进行了估算，并根据合适的模型进行了估算。此外，我们还对(La_&lt；1-Z&gt；Pr_Z)_&lt；1.2&gt；Sr_&lt；1.8&gt；Mn_2O_7.的弹性常数进行了测量。在7T的磁场下，该系统在4.2K时发生了绝缘体到金属的相变。我们发现纵向弹性常数S*S伴随着IM相变出现了显著的软化，并且在高场下表现出硬化。这一行为与ET系统有很大不同。这些对不同体系的系统研究有望为Et体系IM相变的起源提供重要的信息。(3)用超声方法研究了RETr_4X_&lt；12&gt；(Re：稀土元素，Tr：过渡金属，X：PNictgen)填充的Skutterudite化合物中的弹性反常现象。到目前为止，已测定了LaFe_4P_(12)、PrFe_4P_(12)、NdFe_4P_(12)、LaRu_4Sb_(12)、CeU_4Sb_(12)和PrRu_4Sb_(12)的弹性常数。在PrFe_4p&lt；12&gt；中发现了(C_&lt；11&gt；-C_&lt；12&gt；)/2的弹性软化。这证实了该体系的4f基态为G_3。弹性常数的奇异场依赖性清楚地表明了四极近藤效应的证据，并且这一效应受磁场的影响很大。较少

项目成果

Y. Nakanishi et al.: "Elastic properties of Nd Fe_4P_<12>"Physica B. 312-313. 827-828 (2002)

Y. Nakanishi 等：“Nd Fe_4P_<12> 的弹性特性”Physica B. 312-313。

M.Matsukawa et al.: "Anisotropic phonon conduction and lattice distortions in colossal-magnetoresistance bilayer manganite (La_<1-z>Prz)_<1.2>Sr_<1.8>Mn_2O_7 (z=0,0.2,0.4 and 0.6) single crystals"Pfys. Rev. B. 67. 104433-1-104433-6 (2003)

M.Matsukawa 等人：“巨型磁阻双层锰矿 (La_<1-z>Prz)_<1.2>Sr_<1.8>Mn_2O_7 (z=0,0.2,0.4 和 0.6) 单层中的各向异性声子传导和晶格畸变

Y.Nakanishi: "Elastic constants of PrFe_4p_<12>in the magnetic field"Phys. Rev. B. 63. 184429 (2001)

Y.Nakanishi：“PrFe_4p_<12>在磁场中的弹性常数”Phys。

T.Simizu, N.Yoshimoto, Y.Nakanishi, M.Nakamura, M.Yoshizawa: "Elastic anomalies of κ-(ET)_2Cu [N(CN)_2]Br associated with the insulator-to-metal crossover"Acta Physica Polonica B. 34. 795-798 (2003)

T.Simizu、N.Yoshimoto、Y.Nakanishi、M.Nakamura、M.Yoshizawa：“与绝缘体与金属交叉相关的 κ-(ET)_2Cu [N(CN)_2]Br 的弹性异常”物理学报波洛尼卡 B.34.795-798 (2003)

M. Matsukawa et al.: "Anisotropic phonon conduction and lattice distortions in colossal-magnetoresistance bilayer manganite (La_<1-Z>Prz)_<1.2>Sr_<1.8>Mn_2O_7 (z=0, 0.2, 0.4 and 0.6) single crystals"Pfys. Rev. B. 67. 104433 (2003)

M. Matsukawa 等人：“巨磁阻双层锰矿 (La_<1-Z>Prz)_<1.2>Sr_<1.8>Mn_2O_7 (z=0、0.2、0.4 和 0.6) 单层中的各向异性声子传导和晶格畸变