| Budget Amount *help |
¥10,600,000 (Direct Cost: ¥10,600,000)
Fiscal Year 2003: ¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 2002: ¥6,700,000 (Direct Cost: ¥6,700,000)
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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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