Abstract：

The study of delafossite metals ABO₂ has recently attracted much attention in that they exhibit fruitful interesting properties, including the highly 2D transport properties and extremely long electron mean free path observed within the noble metal layers of PtCoO₂ and PdCoO₂ [1], making ballistic electron transport in the μm scale realizable. In this talk, I will discuss the results of my scanning tunneling microscopy (STM) studies of two different delafossite materials: PdCoO₂ and PdCrO₂.

First, I will report on a spectroscopic imaging study of the two-dimensional electron gas at the cobaltate surface of PdCoO₂, a correlated oxide system exhibiting giant Rashba-like spin-splitting [2]. Our data reveals a complex quasiparticle interference pattern which, in particular, comprises a rounded-hexagon shaped, hole-like scattering band that disperses with averaged effective masses of ~ -13.0 m_e and ~ -11.1 m_e along the Γ-Κ and Γ-Μ directions, respectively. Through comparison with the results of our tight binding calculations, we demonstrated that the scattering is well described by the pure spin-selection rules, instead of the spin-orbit selection results obeyed by conventional Rashba systems.

Then, I will report on STM findings on the Pd surface layer of PdCrO₂, a frustrated antiferromagnetic metal that exhibits (√3×√3)R120∘ AFM order throughout the Cr lattice. On the Pd surface layer, we observed a non-periodic tiling phase, whose formation was interpreted as due to surface-polarity-driven reconstruction. Its STM appearance and other properties will be discussed in detail.

[1] A. P. Mackenzie, Rep. Prog. Phys. 80, 032501 (2017)

[2] V. Sunko et al., Nature 549, 492-496 (2017)