Multiple quantum oscillation frequencies in $\mathrm{YBa_{2}Cu_{3}O_{6+\delta}}$ and bilayer splitting

TL;DR

This paper models quantum oscillation frequencies in underdoped YBa2Cu3O6+δ, linking them to bilayer splitting and Fermi surface reconstruction, and finds experimental consistency with a renormalized bilayer splitting that varies with doping.

Contribution

It introduces a model connecting quantum oscillations to bilayer splitting and density wave order, highlighting the renormalization of bilayer splitting from band structure predictions.

Findings

Quantum oscillations arise from Landau levels of reconstructed Fermi surface.

Bilayer splitting is significantly renormalized from band structure calculations.

Frequency splitting likely increases with doping, but may be affected by diminishing density wave order.

Abstract

Experiments have revealed multiple quantum oscillation frequencies in underdoped high temperature superconductor $\mathrm{YBa_{2}Cu_{3}O_{6+\delta}}$, corresponding to approximately 10% doping, which contain $\mathrm{CuO}$ bilayers in the unit cell. These unit cells are further coupled along the c-axis by a tunneling matrix element. A model of the energy dispersion that has its roots in the previously determined electronic structure, combined with two-fold commensurate density waves, reveals multiple electron and hole pockets. To the extent that quasiparticles of the reconstructed Fermi surface have finite residues, however small, the formation of Landau levels are the cause of these oscillations and the bilayer splitting and warping of the electronic dispersion along the direction perpendicular to the CuO-planes are firm consequences. We explore this possibility in detail and find overall consistency with experiments. An important conclusion is that bilayer splitting is severely renormalized from the value obtained from band structure calculations. It would be extremely interesting to perform these experiments for higher values of doping. We roughly expect the splitting of the frequencies to increase with doping, but the full picture may be more complex because the density wave order parameter is also expected to decrease with doping, vanishing around the middle of the superconducting dome.