Research of quantum phase transitions under high magnetic field using synchrotron x-rays

在这个研究项目中，我们应用了利用同步加速器X射线的显微技术，如X射线吸收光谱，在低温和高磁场下发生的量子相变，以揭示量子临界状态下的序参数和电子态。在Ce基重费米子化合物中，我们详细测量了Ce的价态随磁场的变化，揭示了磁场是如何抑制4f电子巡游的。在Yb基重费米子化合物中，发现YbAgCu 4中的价态跃迁引起变磁跃迁，并且迄今为止报道的YbRh 2Si 2中的电子异常并不伴随着电子结构的大的变化，例如费米表面重构。

In this research project, we applied microscopic techniques that utilize synchrotron x-rays, such as x-ray absorption spectroscopy, to quantum phase transitions that occur at low temperatures and in high magnetic fields in order to reveal the order parameters and the electronic states in the quantum critical regime. In Ce-based heavy Fermion compounds, we measured the Ce valence as a function of magnetic field in detail and revealed how itinerancy of the 4f electrons is suppressed by magnetic field. In Yb-based heavy Fermion compounds, it was found that a valence transition gives rise to the metamagnetic transition in YbAgCu4 and that the electronic anomalies reported so far in YbRh2Si2 are not accompanied by a large change in electronic structure, such as Fermi surface reconstruction.