Comparative study of rare earth hexaborides using high resolution angle-resolved photoemission

摘要

Strong electron correlations in rare earth hexaborides can give rise to avariety of interesting phenomena like ferromagnetism, Kondo hybridization,mixed valence, superconductivity and possibly topological characteristics. Thetheoretical prediction of topological properties in SmB$_{6}$ and YbB$_{6}$,has rekindled the scientific interest in the rare earth hexaborides, andhigh-resolution ARPES has been playing a major role in the debate. Theelectronic band structure of the hexaborides contains the key to understand theorigin of the different phenomena observed, and much can be learned bycomparing the experimental data from different rare earth hexaborides. We haveperformed high-resolution ARPES on the (001) surfaces of YbB$_{6}$, CeB$_{6}$and SmB$_{6}$. On the most basic level, the data show that the differences inthe valence of the rare earth element are reflected in the experimentalelectronic band structure primarily as a rigid shift of the energy position ofthe metal 5$\textit{d}$ states with respect to the Fermi level. Although theoverall shape of the $\textit{d}$-derived Fermi surface contours remains thesame, we report differences in the dimensionality of these states between thecompounds studied. Moreover, the spectroscopic fingerprint of the 4$\textit{f}$states also reveals considerable differences that are related to theircoherence and the strength of the $\textit{d}$-$\textit{f}$ hybridization. Forthe SmB$_6$ case, we use ARPES in combination with STM imaging and electrondiffraction to reveal time dependent changes in the structural symmetry of thehighly debated SmB$_{6}$(001) surface. All in all, our study highlights thesuitability of electron spectroscopies like high-resolution ARPES to providelinks between electronic structure and function in complex and correlatedmaterials such as the rare earth hexaborides.