Optical and structural studies of a two-dimensional organic Mott insulator dimethylphenazine-tetrafluorotetracyanoquinodimethane
Optical and structural studies of a two-dimensional organic Mott insulator dimethylphenazine-tetrafluorotetracyanoquinodimethane
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二维有机莫特绝缘体二甲基吩嗪-四氟四氰基醌二甲烷的光学和结构研究
DOI：
10.1103/physrevb.84.085136
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发表时间：
2011
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et al
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作者：
M.Ohkura;Y.Ishige;et al
通过光学反射光谱和X射线结构分析研究了有机电荷转移配合物MP-TCNQF（MP：5,10-二氢-5,10-二甲基吩嗪；TCNQF：2,3,5,6-四氟-7,7,8,8-四氰基醌二甲烷）的电子结构。这是一种离子化合物，具有独特的准二维（2D）晶体结构，其中MP的供体（）分子和TCNQF的受体（）分子分别沿[100]方向堆叠，and和分子也沿[111]方向交替堆叠。我们评估了室温下相邻分子之间的转移能()、沿[100]方向的相邻分子之间的转移能()以及沿[111]方向的相邻分子之间的转移能()分别为43 meV、29 meV和67 meV。这表明形成了各向异性的二维电子结构。通过将偏振反射率光谱得到的介电常数ε2的虚部光谱与分别由一维堆叠和堆叠组成的K-TCNQF的吸收光谱和MP-PF的ε2光谱进行比较，发现MP-TCNQF中的光学间隙对应于莫特间隙跃迁fromto、theto跃迁和theto跃迁或等效于位于较高处的电荷转移(CT)跃迁。能量。在结构和磁相变温度～122 K以下，通过分子和分子的位移形成自旋单线态。人们发现分子位移的模式非常独特，表明相变不能归因于类自旋 Peierls 机制。从分子位移的温度依赖性以及莫特带隙转变和 CT 转变讨论相变的性质。
Electronic structure of an organic charge-transfer complex, MP-TCNQF(MP: 5,10-dihydro-5,10-dimethylphenazine; TCNQF: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), was investigated by means of optical reflection spectroscopy and x-ray structural analyses. This is an ionic compound and has a unique quasi-two-dimensional (2D) crystal structure in which donor () molecules of MP and acceptor () molecules of TCNQFstack respectively along the [100] direction, andandmolecules also stack alternately along the [111] direction. We evaluated the transfer energy() between the neighboringmolecules,() between the neighboringmolecules along the [100] direction, and() between the neighboringandmolecules along the [111] direction to be 43 meV, 29 meV, and 67 meV at room temperature, respectively. This demonstrates that an anisotropic 2D electronic structure is formed. By comparing the spectra of the imaginary part of the dielectric constant ɛ2 obtained from the polarized reflectivity spectra with the absorption spectrum of K-TCNQFand the ɛ2 spectra of MP-PF, which are composed of 1Dstacks andstacks, respectively, it was revealed that in MP-TCNQFthe optical gap corresponds to the Mott gap transition fromto, and thetotransition and thetotransition or equivalently the charge-transfer (CT) transition located at the higher energies. Below the structural and magnetic phase transition temperature∼ 122 K, spin-singlet states are formed via displacements of bothandmolecules. The pattern of molecular displacements was found to be very unique, indicating that the phase transition cannot be attributed to a spin-Peierls-like mechanism. The nature of the phase transition is discussed from the temperature dependences of molecular displacements as well as of the Mott-gap transition and the CT transition.