Loss of nodal quasiparticle integrity in underdoped YBa2Cu3O6+x

TL;DR

This study investigates the evolution of quasiparticle integrity in underdoped YBa2Cu3O6+x using ARPES, revealing a loss of nodal quasiparticle weight at low doping levels, indicating a departure from Fermi liquid behavior and a crossover to Mott physics.

Contribution

The paper provides the first direct measurement of quasiparticle weight Z across a wide doping range in YBCO, demonstrating its vanishing at low doping and supporting a transition to Mott physics.

Findings

Quasiparticle weight Z follows mean-field predictions in overdoped samples.

Nodal quasiparticle weight Z_N vanishes below p~0.10-0.15.

Results suggest a rapid crossover to Mott physics in underdoped cuprates.

Abstract

Arguably the most intriguing aspect of the physics of cuprates is the close proximity between the record high-Tc superconductivity (HTSC) and the antiferromagnetic charge-transfer insulating state driven by Mott-like electron correlations. These are responsible for the intimate connection between high and low-energy scale physics, and their key role in the mechanism of HTSC was conjectured very early on. More recently, the detection of quantum oscillations in high-magnetic field experiments on YBa2Cu3O6+x (YBCO) has suggested the existence of a Fermi surface of well-defined quasiparticles in underdoped cuprates, lending support to the alternative proposal that HTSC might emerge from a Fermi liquid across the whole cuprate phase diagram. Discriminating between these orthogonal scenarios hinges on the quantitative determination of the elusive quasiparticle weight Z, over a wide range of hole-doping p. By means of angle-resolved photoemission spectroscopy (ARPES) on in situ doped YBCO, and following the evolution of bilayer band-splitting, we show that the overdoped metal electronic structure (0.25<p<0.37) is in remarkable agreement with density functional theory and the Z=2p/(p+1) mean-field prediction. Below p~0.10-0.15, we observe the vanishing of the nodal quasiparticle weight Z_N; this marks a clear departure from Fermi liquid behaviour and -- consistent with dynamical mean-field theory -- is even a more rapid crossover to the Mott physics than expected for the doped resonating valence bond (RVB) spin liquid.