Bulk States in PtCoO $$_{2}$$ 2 and PdCoO $$_{2}$$ 2

Abstract

Understanding the exceptionally high conductivity of delafossite oxides, as well as the unconventional transport properties it causes, requires a good knowledge of their electronic structure. As discussed in Sect. 1.1.3, prior to the work presented here both quantum oscillation and photoemission measurements were performed on the Pd based delafossites, PdCoO 2 and PdCrO 2 [1-6], while the available PtCoO 2 crystals were too small to make such experiments feasible. In Sects. 4.1 and 4.2 of this chapter I report the first measurements of the electronic structure of PtCoO 2 , as well as new ARPES measurements on PdCoO 2 which will be used to compare the two compounds. As discussed in Sect. 2.6.5, the majority of the photoemission measurements on delafossites reveal signatures of both bulk and surface states. However, one of our cleaves from each of PtCoO 2 and PdCoO 2 showed no signs of surface states arising from either of the surface terminations. This greatly simplifies the analysis and interpretation of the bulk electronic structure, so I will concentrate on the results obtained from these two samples. The effective masses and electron counts extracted from the photoemission data will also be compared to density functional theory calculations and bulk-sensitive quantum oscillation measurements. As was already discussed in the context of the previous measurements on PdCoO 2 , the band which crosses the Fermi level in the Pd and Pt-based delafossite metals is very two dimensional. The experimental line-width is therefore simply related to the self-energy, making the delafossites candidate model systems to investigate the influence of many-body interactions on the quasiparticle dispersions. Additionally, the large bandwidth of the metallic band in principle allows for the analysis of electron-electron interactions over a large energy range of ∼1 eV. Such analysis is performed, and its limitations discussed, in Sect. 4.3.