Angle-dependence of quantum oscillations in YBa2Cu3O6.59 shows free spin behaviour of quasiparticles

TL;DR

This study uses a genetic algorithm to analyze quantum oscillations in YBa2Cu3O6.59, revealing that quasiparticles behave as nearly free spins and providing insights into the Fermi surface and spin-related phenomena in cuprates.

Contribution

It introduces a genetic algorithm approach to model quantum oscillations, identifying Zeeman splitting effects and quasiparticle spin behavior in cuprate superconductors.

Findings

Quasiparticles behave as nearly free spins.

Fermi surface modeled as two small quasi-2D cylinders.

Zeeman splitting observed, indicating spin behavior.

Abstract

Measurements of quantum oscillations in the cuprate superconductors afford a new opportunity to assess the extent to which the electronic properties of these materials yield to a description rooted in Fermi liquid theory. However, such an analysis is hampered by the small number of oscillatory periods observed. Here we employ a genetic algorithm to globally model the field, angular, and temperature dependence of the quantum oscillations observed in the resistivity of YBa2Cu3O6.59. This approach successfully fits an entire data set to a Fermi surface comprised of two small, quasi-2-dimensional cylinders. A key feature of the data is the first identification of the effect of Zeeman splitting, which separates spin-up and spin-down contributions, indicating that the quasiparticles in the cuprates behave as nearly free spins, constraining the source of the Fermi surface reconstruction to something other than a conventional spin density wave with moments parallel to the CuO2 planes.