Neutral-Ionic Phase Transition in Organic Crystals and Thin Films

有机晶体和薄膜中的中性离子相变

• 批准号: 62460026
• 负责人: KOSHIHARA Shin-ya
• 金额: $ 4.29万
• 依托单位: University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1987
• 资助国家: 日本
• 起止时间: 1987 至 1988
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-62460026/
• 关键词: neutral-ionic(NI) phase transition; organic charge-transfer(CT) compound; negative resistance effect; charged soliton; NI domain wall; photo-induced effect; 負性抵抗特性; 光誘起スペクトル; 中性-イオン性転移; 負性抵抗スイッチング現象; NIドメイン壁; 光励起; 非線形誘電応答; 中性ーイオン性転移; 電荷移動錯体

The neutral-ionic (NI) phase transition in organic mixed-stack charge-transfer (CT) coupounds, that is the valence change from the neutral DA to ionic DA stack, has been investigated with particular emphaisis on its dynamical aspect. First, the anomalous charge-transport properties associated with the NI transition have been revealed, which are, for example, expontial increase of conductivity with hydrostatic pressure and strong nonlinear field-dependence followed by the negative resistance effect. The latter effect leads to the current switching phenomena with the temperature-dependent hysteresis loop, when an appropriate load resister is connected in series to the sample. These effects are considered to be correlated with the dynamics of low-energy excitations, such as charged solitons and NI domain walls, characteristic of the coumpound near the N-I phase boundary. Dynamical response was further pursued by measurements of frequency-dependent dielectric constant as well as photo-induced reflectance change near the NI phase transition temperature. The relaxation time of dielectric constant show the thermally activated behaviour with well-defined activation enrgy, which nearly coincides with that for charge transport. The dielectric constant, which is very large (>10^4) for the low dc field, show the strong nonlinearity at temperatures near the NI phase transition. These results indicate that the confined NI domain wall-pairs are responsible for such an anomalous dielectric respnse and the dissociation of these charged pair play an important role in nonlinear transport. The large photo-induced signal could be detected in the I phase where the DA stacks are dimerized due to the spin-lattice interaction. The trasient response and photoinduced spectral change can be interpreted in terms of the photo-injection of NI domain walls into the dimerized ionic DA stack.

有机混合堆栈电荷转移（CT）政变中的中性离子（Ni）相变（即从中性DA到离子DA堆栈的价变化）已在其动力学方面进行了特定的透明度。首先，已经揭示了与Ni转变相关的异常电荷转移特性，例如，这些特性是通过静水压力和强型非线性场依赖性的电导率的地端增加，然后是负电阻效应。当将适当的载荷响应器串联连接到样品时，后一种效应带来了与温度依赖性磁滞回路的当前开关现象。这些作用被认为与低能激发的动力学相关，例如带电的孤子和Ni结构域壁，这是N-I相边界附近COUMPOUND的特征。通过测量频率依赖性介电常数以及在Ni相变温度附近的反射率变化来进一步追求动力响应。介电常数的松弛时间显示了具有明确定义的激活ENRGY的热激活行为，这几乎与电荷运输相吻合。对于低直流场的介电常数非常大（> 10^4），显示了Ni相变的温度下的强非线性。这些结果表明，受限制的Ni结构域壁对负责这种异常的介电作用，而这些带电对的对分离在非线性转运中起着重要作用。在I相中，由于自旋晶格相互作用而二聚二聚体可以检测到大型光诱导的信号。可以用将Ni域壁注射到二聚体离子DA堆栈的照片上来解释带有光诱导的光谱变化。

项目成果

K.Takaoka;Y.Kaneko;H.Okamoto;Y.Tokura;T.Koda;T.Mitani;G.Saito: Phys.Rev.B. 36. 3884-3887 (1987)

K.Takaoka；Y.Kaneko；H.Okamoto；Y.Tokura；T.Koda；T.Mitani；G.Saito：Phys.Rev.B。

H.Okamoto;T.Komatsu;Y.Iwasa;T.Koda;Y.Tokura;S.Koshihara;T.Mitani;G.Saito: Synthetic Metals. 27. B189-B196 (1988)

H.Okamoto；T.Komatsu；Y.Iwasa；T.Koda；Y.Tokura；S.Koshihara；T.Mitani；G.Saito：合成金属。

Y,Iwasa;T.Koda;S.Koshihara;Y.Tokura;N.Iwasawa;G.Saito: Phys.Rev.B.

Y，Iwasa；T.Koda；S.Koshihara；Y.Tokura；N.Iwasawa；G.Saito：Phys.Rev.B。

H.Okamoto;T.Koda;Y.Tokura;T.Mitani;G.Saito: Phys.RevB,.

H.Okamoto；T.Koda；Y.Tokura；T.Mitani；G.Saito：Phys.RevB，。

T.Mitani;Y.Kaneko;S.Tanuma;Y.Tokura;T.Koda;G.Saito: Phys.Rev.B. 35. 427-429 (1987)

T.Mitani；Y.Kaneko；S.Tanuma；Y.Tokura；T.Koda；G.Saito：Phys.Rev.B。