On the break in the single-particle energy dispersions and the `universal' nodal Fermi velocity in the high-temperature copper-oxide superconductors

TL;DR

This paper analyzes angle-resolved photoemission data revealing a universal Fermi velocity in high-temperature cuprate superconductors and discusses the implications of observed dispersion breaks and velocity discontinuities.

Contribution

It provides a rigorous analysis of experimental data showing a universal nodal Fermi velocity and a sudden change at a characteristic wavevector in cuprates.

Findings

Fermi velocities are nearly the same across different compounds and doping levels.

A sudden change in Fermi velocity occurs at a specific wavevector k_*.

The change in Fermi velocity is most pronounced in underdoped samples.

Abstract

Recent data from angle-resolved photoemission experiments published by Zhou et al. [Nature, Vol. 423, 398 (2003)] concerning a number of hole-doped copper-oxide-based high-temperature superconductors reveal that in the nodal directions of the underlying square Brillouin zones (i.e. the directions along which the d-wave superconducting gap is vanishing) the Fermi velocities for some finite range of k inside the Fermi sea and away from the nodal Fermi wavevector k_F are to within an experimental uncertainty of approximately 20% the same both in all the compounds investigated and over a wide range of doping concentrations and that, in line with earlier experimental observations, at some characteristic wavevector k_* away from k_F the Fermi velocities undergo a sudden change, with this change (roughly speaking, a finite discontinuity) being the greatest (smallest) in the case of underdoped (overdoped) compounds. In this paper we present a rigorous analysis concerning the implications of these observations. [Short abstract]