Pressure-Induced Electron Transitions and Physical Anomalies in Pd-Ce Alloys of the f-Electron Systems

在这项研究中，我们在KEK光子工厂的BL-7C使用传统的金刚石砧压电池（DAC）和聚焦同步加速器光束开发了荧光XANES测量方法。用该方法测量了PdCe和GaCe合金在高达10 GPa的高压下的Ce-L_<III> XANES光谱。我们证实了这些合金相中4f电子的压力诱导跃迁（Ce价的压力变化）。为了检验Ce价与异常电阻率（致密近藤效应）之间的关系，我们还进行了高压电阻率测量和高压x射线衍射实验，得到了以下结果：在GaCe合金相中，L_<III> XANES荧光光谱测得的Ce价从3.02（室温）到3.14 （9 GPa）不等。由于PdCe中的Ce价具有类似的压力依赖性，因此外部压力促进了合金相中4f^1*4f^0的电子跃迁。在GaCe合金相中，与PdCe相一样，当外加压力达到约6 GPa时，致密近藤效应得到强烈增强。当压力大于6 gpa时，效果逐渐减弱。GaCe的体积随压力或可压缩性的下降速率明显大于pdce。有一个最合适的Ce-Ce原子距离，或Ce价，为明显的致密近藤效应的外观。

In this study, we have developed the fluorescence XANES measurement method using a conventional diamond anvil pressure cell (DAC) and a focused synchrotron beam at BL-7C of the Photon Factory in KEK.By this method, Ce-L_<III> XANES spectra were measured for PdCe and GaCe alloys under various high pressures up to-10 GPa. We confirmed the pressure-induced-transition of 4f electrons (the pressurechanges of Ce valence) in these alloy phases. We also carrid out high pressure electrical resistivity measurements and high pressure X-ray diffraction experiments in order to examine the relationship between the Ce valence and the anomalous resistivity (the dense Kondo effect) , and the following results were obtained.1.The Ce valence estimated from the fluorescence L_<III> XANES spectra varies from 3.02 (at ambient pressure) to 3.14 (at 9 GPa) in GaCe alloy phases. Since the Ce valence in PdCe has the similar pressure dependence, the electron transition of 4f^1*4f^0 in alloy-phases is promoted by the external pressure.2.In the GaCe alloy phase, the dense Kondo effect is strongly enhanced by external pressure up to about 6 GPa as in the PdCe phase. The effect becomes weaker gradually with pressure above 6 GPa.3.The rate of decrease in volume with pressure, or the compressibility, of GaCe is remarkably larger than that of PdCe.4.There is a most suitable Ce-Ce atomic distance, or Ce valence, for the distinct appearance of dense Kondo effect.