High-energy kink in high-temperature superconductors

TL;DR

This paper reveals a high-energy kink at around 350 meV in cuprate superconductors, suggesting a more complex electron interaction mechanism than previously thought, which could impact understanding of high-temperature superconductivity.

Contribution

The study identifies a significant high-energy renormalization feature in cuprates, expanding the understanding of electron interactions beyond the well-studied low-energy kink.

Findings

Majority of electron dispersion renormalization occurs at ~350 meV

Low-energy kink at ~50 meV is only a small part of the total effect

High-energy kink presents new challenges for superconductivity theories

Abstract

In conventional metals, electron-phonon coupling, or the phonon-mediated interaction between electrons, has long been known to be the pairing interaction responsible for the superconductivity. The strength of this interaction essentially determines the superconducting transition temperature TC. One manifestation of electron-phonon coupling is a mass renormalization of the electronic dispersion at the energy scale associated with the phonons. This renormalization is directly observable in photoemission experiments. In contrast, there remains little consensus on the pairing mechanism in cuprate high temperature superconductors. The recent observation of similar renormalization effects in cuprates has raised the hope that the mechanism of high temperature superconductivity may finally be resolved. The focus has been on the low energy renormalization and associated "kink" in the dispersion at around 50 meV. However at that energy scale, there are multiple candidates including phonon branches, structure in the spin-fluctuation spectrum, and the superconducting gap itself, making the unique identification of the excitation responsible for the kink difficult. Here we show that the low-energy renormalization at ~50 meV is only a small component of the total renormalization, the majority of which occurs at an order of magnitude higher energy (~350 meV). This high energy kink poses a new challenge for the physics of the cuprates. Its role in superconductivity and relation to the low-energy kink remains to be determined.