Study on valence transition of rare earth compounds

为了揭示YbInCu4在~40 K时的价跃迁机理，我们利用硬X射线光电发射光谱（HAXPES）研究了Cd和Sn位于元素周期表两侧的YbXCu4（X=Cd, Sn）的电子结构，并与YbInCu4的实验结果进行了比较。结果表明，YbInCu4在Cu位点的导电带电子数最多。认为电子很容易从Cu位转移到Yb位，这与YbInCu4的价跃迁密切相关。我们注意到最近合成的近藤晶格YbNi3X9 （X=Al, Ga）与YbInCu4的高温相和低温相相似，并对这些化合物进行了HAXPES分析。通过比较，我们提出了YbInCu4的价跃迁机制是由于导电带电子转移到yb4f轨道上。

In order to reveal the mechanism of valence transition of YbInCu4 at ~40 K, we have investigated electronic structure of YbXCu4(X=Cd, Sn), where Cd and Sn are located just in both sides in the periodic table by means of hard x-ray photoemission spectroscopy (HAXPES) and compared the experimental results with those of YbInCu4. As the result, we obtained the results suggesting that the number of the conduction-band electrons at the Cu site is the greatest for YbInCu4. It is considered that electrons are easily transferred from the Cu to Yb sites, which would closely be related to the valence transition of YbInCu4. We noticed that the recently synthesized Kondo lattices YbNi3X9 (X=Al, Ga) are similar to the high- and low-temperature phases of YbInCu4 and carried out HAXPES for these compounds. From the comparison, we proposed the mechanism that the valence transition of YbInCu4 takes place due to the transfer of the conduction-band electrons to the Yb 4f orbitals.