Doping-dependent nodal Fermi velocity in Bi-2212 revealed by high-resolution ARPES

TL;DR

This study uses high-resolution laser ARPES to investigate how the nodal Fermi velocity in Bi-2212 varies with doping, revealing a doping-dependent low-energy kink and non-universal velocity behavior.

Contribution

It provides the first systematic doping-dependent analysis of the low-energy kink in Bi-2212, showing its robustness and impact on nodal velocity, challenging previous assumptions.

Findings

Nodal Fermi velocity decreases with underdoping.

The low-energy kink is ubiquitous across doping levels.

Discrepancies with thermal conductivity measurements are addressed.

Abstract

The improved resolution of laser-based angle-resolved photoemission spectroscopy (ARPES) allows reliable access to fine structures in the spectrum. We present a systematic, doping-dependent study of a recently discovered low-energy kink in the nodal dispersion of Bi2Sr2CaCu2O8+d (Bi-2212), which demonstrates the ubiquity and robustness of this kink in underdoped Bi-2212. The renormalization of the nodal velocity due to this kink becomes stronger with underdoping, revealing that the nodal Fermi velocity is non-universal, in contrast to assumed phenomenology. This is used together with laser-ARPES measurements of the gap velocity, v2, to resolve discrepancies with thermal conductivity measurements.