ARPES investigations of proposed topological low carrier density Ce and Yb compounds

In the search for new strongly correlated topological materials, going beyond the initial candidate material SmB₆, a number of issues arise in the angle-resolved photoemission (ARPES) interpretations of observed Dirac-like band dispersions and two-dimensionality. In particular the example of YbB₆, a divalent small-gap semiconductor at ambient pressure, misinterpreted as a topological Kondo insulator, highlights issues of surface termination, polarity and band-bending, V-shaped non-parabolicity of band dispersions arising from small gaps, degrees of two-dimensionality, interpretation of circular dichroism, and use of theoretical band-gap correction methods. With such lessons in mind, we focus attention on three low carrier density heavy fermion systems of (i) YbPtBi, an ultra-heavy-fermion half-Heusler semimetal, (ii) CeSb and related fcc monopnictide semimetals, and (iii) CeRhSb, a Kondo insulator with predicted Mobius-type surface state dispersion. We critically assess the ARPES evidence for their proposed topological properties and highlight the tool of surface alkali-dosing to help distinguish surface state scenarios. In addition, we report progress in the understanding of their various bulk properties including CEF splittings, temperature-dependence of f-states and magnetic ground states.
In collaboration with Sooyoung Jang, J.G. Analytis, J.W. Allen, Jeongsoo Kang, B.I. Min, C.J. Kang, J.H. Shim, and Z. Fisk.