Study of valence fluctuation, quantum critical phenomena, and superconductivity in heavy fermion systems

在稀土化合物中，f电子具有局域性质，但有趣的物理性质是通过f和传导电子之间的杂化实现的，这是由于RKKY相互作用和近藤效应之间的相互作用而被理解的。本文用共振X射线发射光谱（RXES）研究了量子临界点附近的电子结构。我们还使用了光电子能谱补充在环境压力。在RXES研究中，我们通过施加压力来控制近藤温度。我们发现了方钴矿Yb_xFe_4Sb_2中Yb价态<12>随温度变化的反常现象。

In rare-earth compounds f electrons have local nature, but interesting physical properties are realized via hybridization between f and conduction electrons, which has been understood due to the interplay between the RKKY interaction and the Kondo effect. Here we have studied the electronic structure around quantum critical point by using resonant x-ray emission spectroscopy (RXES). We also used photoelectron spectroscopy complementarily at ambient pressure. In the RXES studies we control the Kondo temperature by applying pressure. We newly found anomales in Yb valence of skutterudite Yb_xFe_4Sb_<12> in the temperature dependence.