Missing Quasiparticles and the Chemical Potential Puzzle in the Doping Evolution of the Cuprate Superconductors

TL;DR

This study uses advanced photoemission techniques to investigate the evolution of electronic structure and chemical potential in doped cuprate superconductors, revealing failures of conventional quasiparticle theory and proposing a new model for quasiparticle growth.

Contribution

It introduces a model where quasiparticles are negligible at half filling and grow with doping, unifying dispersion, Fermi wavevector, and chemical potential behavior.

Findings

Failure of conventional quasiparticle theory in cuprates

Chemical potential shifts within the Mott gap

Quasiparticles grow with doping from negligible to significant

Abstract

The evolution of Ca$_{2-x}$Na$_{x}$CuO$_{2}$Cl$_{2}$ from Mott insulator to superconductor was studied using angle-resolved photoemission spectroscopy. By measuring both the excitations near the Fermi energy as well as non-bonding states, we tracked the doping dependence of the electronic structure and the chemical potential with unprecedented precision. Our work reveals failures in the conventional quasiparticle theory, including the broad lineshapes of the insulator and the apparently paradoxical shift of the chemical potential within the Mott gap. To resolve this, we develop a model where the quasiparticle is vanishingly small at half filling and grows upon doping, allowing us to unify properties such as the dispersion and Fermi wavevector with the behavior of the chemical potential.