Chen Bijuan, Tian Mingfeng, Zhang Jurong, Li Bing, Xiao Yuming, Chow Paul, Kenney-Benson Curtis, Deng Hongshan, Zhang Jianbo, Sereika Raimundas, Yin Xia, Wang Dong, Hong Xinguo, Jin Changqing, Bi Yan, Liu Hanyu, Liu Haifeng, Li Jun, Jin Ke, Wu Qiang, Chang Jun, Ding Yang, Mao Ho-Kwang
Center for High-Pressure Science and Technology Advanced Research, Beijing 100094, China.
Institute of Applied Physics and Computational Mathematics, Beijing 100088, China.
Phys Rev Lett. 2022 Jul 1;129(1):016401. doi: 10.1103/PhysRevLett.129.016401.
Valence transition could induce structural, insulator-metal, nonmagnetic-magnetic and superconducting transitions in rare-earth metals and compounds, while the underlying physics remains unclear due to the complex interaction of localized 4f electrons as well as their coupling with itinerant electrons. The valence transition in the elemental metal europium (Eu) still has remained as a matter of debate. Using resonant x-ray emission scattering and x-ray diffraction, we pressurize the states of 4f electrons in Eu and study its valence and structure transitions up to 160 GPa. We provide compelling evidence for a valence transition around 80 GPa, which coincides with a structural transition from a monoclinic (C2/c) to an orthorhombic phase (Pnma). We show that the valence transition occurs when the pressure-dependent energy gap between 4f and 5d electrons approaches the Coulomb interaction. Our discovery is critical for understanding the electrodynamics of Eu, including magnetism and high-pressure superconductivity.
价态转变能够在稀土金属及其化合物中诱发结构、绝缘体 - 金属、非磁性 - 磁性以及超导转变，然而由于局域4f电子的复杂相互作用及其与巡游电子的耦合，其背后的物理机制仍不明确。元素金属铕（Eu）中的价态转变一直是一个有争议的问题。利用共振X射线发射散射和X射线衍射，我们对铕中4f电子的状态进行加压，并研究其高达160吉帕斯卡的价态和结构转变。我们提供了令人信服的证据，证明在约80吉帕斯卡时发生了价态转变，这与从单斜（C2/c）到正交相（Pnma）的结构转变相吻合。我们表明，当4f和5d电子之间与压力相关的能隙接近库仑相互作用时，就会发生价态转变。我们的发现对于理解铕的电动力学，包括磁性和高压超导性至关重要。
