Search for Topological Properties of Correlated Electron Systems SmB\(_{6}\)-YbB\(_{6}\)-CeB\(_{6}\) and CeBi/CeSb

Abstract

Three-dimensional topological insulators (3D TIs) have been experimentally discovered seven years ago, and since then over one hundred materials have been identified as such\(^{[1]}\). The advantage of studying 3D TIs is the ability for their existence at room temperature and no magnetic fields, allowing for both the study of electronic transport and other properties of their surface states via pointcontact spectroscopy (PCS) and the analysis of their band structure via angleresolved photoemission spectroscopy (ARPES). The spin-ARPES technique, allowing probing new topological order in solids, has recently been used to discover new 3D topological orders, among which is the topological Kondo insulator (TKI), where the topological surface states are in a so-called Kondo gap, not the Bloch gap, as in 3D TIs. The Kondo insulators are found in rare-earth based materials with f-electron degrees of freedom. In the past few years, the samarium hexaboride (SmB\(_{6}\)) compound was predicted to be a possible TKI, and the search is on for more compounds exhibiting Kondo insulation. One such compound, cerium hexaboride (CeB\(_{6}\)), has recently attracted interest\(^{[2]}\) due to its several transitions at very low temperatures and intense ferromagnetic fluctuations at low energy, despite being characterized as an antiferromagnetic metal. In parallel, exploring the properties of cerium pnictogen (CeX) compounds would offer an interpretation of a related (cerium-based) strongly correlated-electron system in terms of any potential degeneracy and hybridization detected. My work will focus on investigating the properties and electronic structure of CeB\(_{6}\) in the context of the "family" of hexaborides SmB\(_{6}\)-YbB\(_{6}\)-CeB\(_{6}\)-BaB\(_{6}\), and relate it to the properties detected for CeX compounds. I will describe the photon energy dependent dispersion relationships and corresponding temperature dependence in (1) the hexaborides leading up to CeB\(_{6}\) and (2) the monopnictide CeBi/CeSb pair, measured via ARPES, followed by first-principles calculations and theoretical validation. Other methods, such as crystal growth of an earlier topological insulator and its characterization via ARPES and X-ray diffraction, are an additional part of my analysis and constitute a prototype study that was necessary to embark on this research.