Direct observation of strong correlations near the band insulator regime of Bi misfit cobaltates

TL;DR

This study uses ARPES to explore the electronic structure of Bi misfit cobaltates, revealing strong many-body interactions and magnetic excitations near the band insulator regime, similar to Na cobaltates.

Contribution

First ARPES measurement of Fermi Surface in Bi misfit cobaltates showing similarity to Na cobaltates and identifying strong many-body effects.

Findings

Spectral weight transfer indicates stronger interactions near band insulator regime.

Lineshape of cobaltates is of the 'peak-dip-hump' type due to many-body effects.

Electronic structure similar to Na cobaltates.

Abstract

We present the first angle-resolved photoemission (ARPES) measurement of Fermi Surface in the "misfit" cobaltate [Bi2Ba2O4].[CoO2]~2. This compound contains the same triangular Co planes as Na cobaltates, but in a different 3D environment. Our data establish the similarity of their electronic structure. We propose that the peculiar lineshape of all cobaltates is of the "peak-dip-hump" type, due to strong many-body effects. We detect a progressive transfer of spectral weight from the quasiparticle feature near Ef to a broad hump in misfit phases where Ba is replaced by Sr or Ca. This indicates stronger many-body interactions in proximity of the band insulator regime, which we attribute to the presence of unusual magnetic excitations.