Layer-resolved many-electron interactions in delafossite PdCoO2 from standing-wave photoemission spectroscopy

Inna Vishik,Seongshik Oh,Juhan Matthias Kahk,Qiyang Lu,William C. Chueh,Gaurab Rimal,Johannes Lischner,Matthew Brahlek,Slavomir Nemsak,Henrique Martins

doi:10.1038/s42005-021-00643-y

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 VB 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.

Highlights

When a three-dimensional material is constructed by stacking different two-dimensional layers into an ordered structure, new and unique physical properties can emerge
In conjunction with advanced many-body calculations, we provide a comprehensive understanding of the electronic structure of PdCoO2
The natural anisotropy of delafossite materials, which originates from the stacking of metallic Pd layers and Mott-insulating CoO2 layers, drastically affects the electron–electron as well as electron–plasmon interactions in this material

Summary

Introduction

When a three-dimensional material is constructed by stacking different two-dimensional layers into an ordered structure, new and unique physical properties can emerge. While most materials fall into one or the other category, it is intriguing to consider what will happen when the two regimes coexist side-by-side in the same crystal structure Delafossite oxides, such as PdCoO2 or PtCoO21,2, have recently emerged as a versatile platform for studying exotic quantum phenomena[3]. These materials can be viewed as heterostructures composed of metallic layers consisting of triangularly coordinated metal atoms (such as Pd or Pt) separated by Mott insulating layers of edge-sharing CoO6 octahedra[4] and are ideal candidates for studying the interplay of weakly and strongly correlated electrons. They suggested that Pd 5s and 4dz[2] orbitals hybridize and that the resulting (5s + 4dz2)

Methods

Results

Conclusion