Electronic structure of sodium tungsten bronzes NaxWO3 by high-resolution angle-resolved photoemission spectroscopy
Electronic structure of sodium tungsten bronzes NaxWO3 by high-resolution angle-resolved photoemission spectroscopy
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DOI：
10.1103/physrevb.75.155116
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发表时间：
2007-04-01
影响因子：
3.7
通讯作者：
Greenblatt, M.
中科院分区：
文献类型：
--
作者：
Raj, S.;Matsui, H.;Greenblatt, M.
利用高分辨角分辨光电子能谱（HR-ARPES）研究了钠钨青铜NaxWO 3在全x范围内的电子结构。实验测定的价带结构进行了比较，从头算能带结构计算的结果。在绝缘和金属相的NaxWO 3的HR-ARPES光谱揭示了金属-绝缘体转变（MIT）的钠钨青铜系统的起源。在绝缘的NaxWO 3中，由于Na+离子在WO 3晶格中的随机分布引起的强烈无序，近E-F态被局域化。虽然由Na掺杂引起的杂质带（能级）的存在经常被用来解释在低浓度下发现的绝缘状态，但从我们的结果中没有发现杂质带（能级）的特征。由于无序和安德森局域化效应，传导电子之间存在长程库仑相互作用，系统是绝缘的。在金属区，E-F附近的状态被填充，并且费米能级随着电子掺杂（x）的增加而刚性地向上移动。由于W5 dt（2g）带的填充，类电子费米面（FS）在Gamma（X）点的体积随Na浓度的增加而逐渐增大。发现E-F的刚性位移可以定性地描述FS的演化。
The electronic structure of sodium tungsten bronzes, NaxWO3, for full range of x is investigated by high-resolution angle-resolved photoemission spectroscopy (HR-ARPES). The experimentally determined valence-band structure has been compared with the results of ab initio band-structure calculation. The HR-ARPES spectra taken in both the insulating and metallic phase of NaxWO3 reveal the origin of metal-insulator transition (MIT) in the sodium tungsten bronze system. In the insulating NaxWO3, the near-E-F states are localized due to the strong disorder caused by the random distribution of Na+ ions in WO3 lattice. While the presence of an impurity band (level) induced by Na doping is often invoked to explain the insulating state found at low concentrations, there is no signature of impurity band (level) found from our results. Due to disorder and Anderson localization effect, there is a long-range Coulomb interaction of conduction electrons; as a result, the system is insulating. In the metallic regime, the states near E-F are populated and the Fermi level shifts upward rigidly with increasing electron doping (x). The volume of electronlike Fermi surface (FS) at the Gamma(X) point gradually increases with increasing Na concentration due to W 5dt(2g) band filling. A rigid shift of E-F is found to give a qualitatively good description of the FS evolution.