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Observation of nanometer-spaced modulated structure causing Large Seebeck coefficient of the Tl compound: Angle-resolved photoemission study

观察导致 Tl 化合物大塞贝克系数的纳米间隔调制结构：角分辨光电研究

基本信息

批准号：
18560014
负责人：
MIMURA Kojiro
金额：
$ 1.82万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

TllnSe_2 with quasi one-dimensional chain structure has attracted much interest because of the structural low-dimensionality, and the interesting electric and thermoelectric properties. Recently, the Seebeck coefficient of TlInSe_2 has then been found to be positive only at temperatures below 473 K, reaching very high values of more than 10^6μV/K below 413 K. It has been pointed out that above record-breaking thermoelectric power may result from the formation of an incommensurate (IC) superlattice phase in TlInSe_2. However, the existence of IC-phase in TlInSe_2 has not been experimentally verified yet, either by the analyses of the electronic structure or by the extended X-ray or neutron scattering examination. In this work, we have studied TlInSe_2 by means of angle-resolved photoemission spectroscopy (ARPES) at 280 and 50K in order to possibly find the imprints of IC-phase in the electronic band structure.The obtained energy bands and the calculated band structure were found to agree well in main futures. The band structure shows quite strong dispersion in the direction perpendicular to the chains and indicates that in fact the one-dimensional electronic features of TlInSe_2 are masked by the strong interchain interactions. The whole spectral features shift rigidly toward lower binding energies with decreasing temperature. The energy gap splitting, furthermore, has been clearly observed in the experimental electronic bands along both directions. A detailed analysis using both experimental and theoretical data was performed and the obtained results were evident of the presence of the IC-phase linked to a certain point on the A-line of the Brillouin zone of TlInSe_2. A self-consistent picture of the phase transition in TlInSe_2 was drawn after discussion using available data for this material. According to this picture, TlInSe_2 at 50K is already a commensurate (C) material while the IC-C phase transition occurs between 280 and 50K.

具有准一维链结构的TllnSe_2由于其结构低维性和有趣的电学和热电性质而引起了人们的广泛关注。最近，发现TlInSe_2的塞贝克系数仅在低于473 K时为正，在低于413 K时达到10^6μV/K以上的很高值。指出上述破纪录的热电功率可能是由于在TlInSe_2中形成了一个不相称的（IC）超晶格相。然而，无论是电子结构分析，还是扩展的x射线或中子散射检查，都尚未证实TlInSe_2中ic相的存在。本文利用角分辨光谱学（ARPES）在280和50K下对TlInSe_2进行了研究，以期在电子带结构中找到ic相的印迹。所得能带与计算能带结构在主要期货中吻合较好。条带结构在垂直于链的方向上表现出较强的色散，表明TlInSe_2的一维电子特性实际上被强链间相互作用所掩盖。随着温度的降低，整个光谱特征刚性地向低结合能方向移动。此外，在两个方向的实验电子带中都清楚地观察到能隙分裂。利用实验和理论数据进行了详细的分析，得到的结果表明，在TlInSe_2的布里渊区A线上存在与某一点相连的ic相。通过对TlInSe_2材料现有数据的讨论，得出了一幅自洽的相变图。从图中可以看出，TlInSe_2在50K时已经是一种相称的(C)材料，而IC-C相变发生在280 ~ 50K之间。