Kinks in the dispersion of strongly correlated electrons

TL;DR

This paper introduces a new purely electronic mechanism causing kinks in the electron dispersion of strongly correlated metals, revealing insights into many-body interactions and challenging existing interpretations of ARPES data.

Contribution

It identifies a novel electronic origin of dispersion kinks in strongly correlated materials, linking their position to Fermi-liquid parameters and uncorrelated band structures.

Findings

Kinks are caused by a purely electronic mechanism in strongly correlated metals.

The position of kinks relates to Fermi-liquid renormalization factors.

ARPES outside the Fermi-liquid regime can reveal new information about correlations.

Abstract

The properties of condensed matter are determined by single-particle and collective excitations and their interactions. These quantum-mechanical excitations are characterized by an energy E and a momentum \hbar k which are related through their dispersion E_k. The coupling of two excitations may lead to abrupt changes (kinks) in the slope of the dispersion. Such kinks thus carry important information about interactions in a many-body system. For example, kinks detected at 40-70 meV below the Fermi level in the electronic dispersion of high-temperature superconductors are taken as evidence for phonon or spin-fluctuation based pairing mechanisms. Kinks in the electronic dispersion at binding energies ranging from 30 to 800 meV are also found in various other metals posing questions about their origins. Here we report a novel, purely electronic mechanism yielding kinks in the electron dispersions. It applies to strongly correlated metals whose spectral function shows well separated Hubbard subbands and central peak as, for example, in transition metal-oxides. The position of the kinks and the energy range of validity of Fermi-liquid (FL) theory is determined solely by the FL renormalization factor and the bare, uncorrelated band structure. Angle-resolved photoemission spectroscopy (ARPES) experiments at binding energies outside the FL regime can thus provide new, previously unexpected information about strongly correlated electronic systems.