Layer-Resolved Many-Electron Interactions in Delafossite PdCoO2 from Standing-Wave Photoemission Spectroscopy

TL;DR

This study combines standing-wave photoemission spectroscopy and ab initio calculations to reveal layer-specific many-electron interactions in PdCoO2, highlighting how different layers exhibit distinct electronic couplings and hybridization effects.

Contribution

It introduces a novel layer-resolved analysis of many-electron interactions in a layered material using combined experimental and computational methods.

Findings

CoO2 layers exhibit strong charge-transfer exciton interactions.

Pd layers show coupling to plasmons.

Hybridized states couple to both excitations, revealing inter-layer hybridization.

Abstract

When a three-dimensional material is constructed by stacking different two-dimensional layers into an ordered structure, new and unique physical properties can emerge. An example is the delafossite PdCoO2, which consists of alternating layers of metallic Pd and Mott-insulating CoO2 sheets. To understand the nature of the electronic coupling between the layers that gives rise to the unique properties of PdCoO2, we revealed its layer-resolved electronic structure combining standing-wave X-ray photoemission spectroscopy and ab initio many-body calculations. Experimentally, we have decomposed the measured valence band spectrum into contributions from Pd and CoO2 layers. Computationally, we find that many-body interactions in Pd and CoO2 layers are highly different. Holes in the CoO2 layer interact strongly with charge-transfer excitons in the same layer, whereas holes in the Pd layer couple to plasmons in the Pd layer. Interestingly, we find that holes in states hybridized across both layers couple to both types of excitations (charge-transfer excitons or plasmons), with the intensity of photoemission satellites being proportional to the projection of the state onto a given layer. This establishes satellites as a sensitive probe for inter-layer hybridization. These findings pave the way towards a better understanding of complex many-electron interactions in layered quantum materials.