Development of high-frequency-compatible scanning tunneling microscope and application to the electronic phase separation in strongly correlated electron systems

高频兼容扫描隧道显微镜的研制及其在强相关电子系统电子相分离中的应用

基本信息

批准号：
14350040
负责人：
HANAGURI Tetsuo
金额：
$ 6.78万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

In this study, we aimed to study the electronic phase separations, which are expected in strongly-correlated-electron systems. The strongly-correlated-electron systems are based on so-called Mott insulators and show many novel phenomena such as high-temperature superconductivity. The study of electronic phase separations demands an experimental technique with nano-scale spatial resolution. Therefore, we used scanning tunneling microscopy/spectroscopy (STM/STS). Also, we tried to develop a new technique, alternating-current STM, to study less conducting samples.The tendency to the electronic phase separation should be strongest around the metal-to-Mott-insulator transition (Mott transition). There are two types of Mott transitions, namely, filling-controlled and bandwidth-controlled Mott transitions. We performed low temperature STM/STS on Ca_<2-x>Na_xCuO_2Cl_2 and Ni(S, Se)_2 which are filling- and bandwidth-controlled systems, respectively. We found that there is marked nano-scale electronic inhomogeneity around the filling-control Mott transition. The apparently "metallic" region increases with increasing doping. This result suggests that the metal-insulator transition in the filling-controlled system is related to the percolation. On the contrary, electronic states of the bandwidth-controlled system are relatively uniform even near the Mott transition. In Ca_<2-x>Na_xCuO_2Cl_2, which is one of the high-temperature superconductors, we found a periodic modulation of the electronic states with a checkerboard-like pattern in a so-called pseudogap phase.As to the alternating-current STM, though we have not completed the construction, we designed a prototype of the high-frequency-compatible STM which can be equipped with semi-rigid coaxial cables. We believe that this new STM will work in near future.

在这项研究中，我们旨在研究电子相分离，这些分离是在强相关的电子系统中预期的。强相关的电子系统基于所谓的莫特绝缘子，并显示了许多新型现象，例如高温超导性。对电子相分离的研究需要使用纳米级空间分辨率的实验技术。因此，我们使用了扫描隧道显微镜/光谱法（STM/STS）。另外，我们试图开发一种新技术，交替流动的STM，以较少研究样品。电子相分离的趋势应在金属到莫特 - 莫特 - 摩托粉碎机过渡（Mott Transition）周围最强。莫特（Mott）过渡有两种类型，即填充控制和带宽控制的莫特过渡。我们在CA__ <2-X>上进行了低温STM/STS，分别是填充和带宽控制系统的Na_xcuo_2cl_2和Ni（s，se）_2。我们发现，在填充控制莫特过渡周围存在明显的纳米级电子不均匀性。显然“金属”区域随着掺杂的增加而增加。该结果表明，填充控制系统中的金属 - 绝缘体过渡与渗透有关。相反，带宽控制系统的电子状态甚至在莫特过渡附近相对均匀。 In Ca_<2-x>Na_xCuO_2Cl_2, which is one of the high-temperature superconductors, we found a periodic modulation of the electronic states with a checkerboard-like pattern in a so-called pseudogap phase.As to the alternating-current STM, though we have not completed the construction, we designed a prototype of the high-frequency-compatible STM which can be equipped with半刚性同轴电缆。我们认为，这个新的STM将在不久的将来起作用。