Inner-shell spectroscopy study on strongly correlated electron systems at 50-Tesla high magnetic fields

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Experimental techniques for the inner-shell magneto-spectroscopy using synchrotron X-rays and pulsed high magnetic fields in the, range of 50 T were developed. We studied rare-earth based strongly correlated materials such as YbInCu_4 and EuNi_2(Si_<1-X>,Ge_X)_2. These materials show significant valence fluctuation at low temperature. Interplay between conduction electrons and localized electrons in matter has been attracting considerable attention because it is one of the most important issues to understand exotic phenomena such as high-T_c superconductivity and the heavy fermions in the so-called strongly correlated electron systems. Valence fluctuation in rare-earth intermetallics is an interesting phenomenon for investigation of the interplay between the conduction electrons and localized f-electrons. The valence states of the rare-earth ions such as Yb and Eu are directly determined in high fields for the first time. As the next step, the experiment of the X-ray magnetic circular dichroism has been performed. The characteristic features due to the significant hybridization in the matter were observed at the spectra in high magnetic fields. These findings are useful for deeper understanding of interplay between conduction and localized electrons.