Origin of Kinks in Energy Dispersion of Strongly Correlated Matter

TL;DR

This paper investigates the origin of low energy kinks in ARPES data of correlated materials, proposing a new extraction method and comparing two theoretical explanations to identify their distinct signatures.

Contribution

It introduces a novel, shape-insensitive protocol for extracting kink parameters and compares local bosonic mode and ECFL theories to explain the kinks.

Findings

The proposed method reliably extracts kink features from experimental data.

ECFL theory aligns with current observations of kinks in cuprates.

Distinct experimental signatures can differentiate between the two theoretical models.

Abstract

We investigate the origin of ubiquitous low energy kinks found in Angle Resolved Photoemission (ARPES) experiments in a variety of correlated matter. Such kinks are unexpected from weakly interacting electrons and hence identifying their origin should lead to fundamental insights in strongly correlated matter. We devise a protocol for extracting the kink momentum and energy from the experimental data which relies solely on the two asymptotic tangents of each dispersion curve, away from the feature itself. It is thereby insensitive to the different shapes of the kinks as seen in experiments. The body of available data is then analyzed using this method. We proceed to discuss two alternate theoretical explanations of the origin of the kinks. Some theoretical proposals invoke local Bosonic excitations (Einstein phonons or other modes with spin or charge character), located exactly at the energy of observed kinks, leading to a momentum independent self energy of the electrons. A recent alternate is the theory of extremely correlated Fermi liquids (ECFL). This theory predicts kinks in the dispersion arising from a momentum dependent self energy of correlated electrons. We present the essential results from both classes of theories, and identify experimental features that can help distinguish between the two mechanisms. The ECFL theory is found to be consistent with currently available data on kinks in the nodal direction of cuprate superconductors, but conclusive tests require higher resolution energy distribution curve data.