The Role of Compound Electronic Structure in Ce-Valence Instabilities

The transition metals are the largest and most chemically diverse group of the periodic table. This has naturally lead transition metal compounds to a prominent position in the study of rare earth valence instabilities—a field where chemical flexibility and diversity are crucial to exploring the instability.1–4 Indeed, experience has shown that differing host electronic structure can alter the often subtle balance between magnetism, spin fluctuations, charge fluctuations and superconductivity in systems near to a valence instability.1–4 In this paper we explore the Ce valence instability in several very broad classes of transition metal compounds. We have several objectives in doing so. First, we wish to illustrate how rare earth valence state determination via L3 x-ray absorption spectroscopy can help draw together materials “tricks of the trade” into a more coherent picture of the underlying valence instability—electronic structure coupling. Second, these L3-valence measurements and their electronic structure tends can be used to efficiently identify new materials in the most interesting portion of the instability6. Finally, we wish to advance the notion that the 4f levels of an unstable valence atom can serve as a marker in the electronic structure of its host material. Moreover, that reading of this marker (via L3-valence determination for example) can in turn be thought of as a probe of the host electronic structure.