Anomalous band renormalization due to high energy $kink$ in the colossal thermoelectric material K$_{0.65}$RhO$_2$

TL;DR

This study reveals a high energy band renormalization in K$_{0.65}$RhO$_2$ caused by a novel high energy kink at 195 meV, linked to high frequency bosonic excitations, impacting its thermoelectric properties.

Contribution

It reports the discovery of a high energy kink at 195 meV in K$_{0.65}$RhO$_2$, indicating an anomalous band renormalization due to high frequency bosonic excitations.

Findings

Observation of a high energy kink at 195 meV.

Momentum-dependent electronic correlations.

Implications for colossal thermoelectric power.

Abstract

We report on low-energy electronic structure and electronic correlations of K$_{0.65}$RhO$_2$, studied using high-resolution angle-resolved photoemission spectroscopy (ARPES) technique and density functional theory (DFT) calculations. We observe a highly correlated hole pocket on the Fermi surface. We further notice that the correlations are momentum dependent. Most importantly, two $kinks$ at binding energies of 75 meV and 195 meV have been observed from the band dispersion in the vicinity of the Fermi level. While the low energy $kink$ at 75 meV can be understood as a result of the electron-phonon interaction, the presence of high energy $kink$ at 195 meV is totally a new discovery of this system leading to an anomalous band renormalization. Based on systematic analysis of our experimental data, we propose high frequency bosonic excitations as a plausible origin of the high energy anomaly. Further, we notice that the high energy anomaly has important implications in obtaining the colossal thermoelectric power of K$_{0.65}$RhO$_2$.