2003 Fiscal Year Final Research Report Summary
Development of high-frequency-compatible scanning tunneling microscope and application to the electronic phase separation in strongly correlated electron systems
| Project/Area Number |
14350040
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied physics, general
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| Research Institution | The University of Tokyo |
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Principal Investigator |
HANAGURI Tetsuo The University of Tokyo, Graduate School of Frontier Sciences, Associate Professor, 大学院・新領域創成科学研究科, 助教授 (40251326)
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| Project Period (FY) |
2002 – 2003
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| Keywords | strongly-correlated-electron system / scanning tunneling microscopy / filling-control / bandwidth-control / electronic phase separation |
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| Research Abstract |
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.
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