Quantum oscillations in a bilayer with broken mirror symmetry: a minimal model for YBa$_2$Cu$_3$O$_{6 + \delta}$

TL;DR

This paper models quantum oscillations in bilayer cuprates, showing that broken mirror symmetry and renormalized interlayer tunneling explain experimental observations in YBCO.

Contribution

It introduces a minimal bilayer model with broken mirror symmetry that reproduces key features of quantum oscillations in YBCO, highlighting the role of magnetic breakdown and quasiparticle renormalization.

Findings

Reproduces oscillation frequency patterns observed in YBCO.

Shows magnetic breakdown depends on broken mirror symmetry.

Suggests quasiparticle weight is less than 1/20.

Abstract

Using an exact numerical solution and semiclassical analysis, we investigate quantum oscillations (QOs) in a model of a bilayer system with an anisotropic (elliptical) electron pocket in each plane. Key features of QO experiments in the high temperature superconducting cuprate YBCO can be reproduced by such a model, in particular the pattern of oscillation frequencies (which reflect "magnetic breakdown" between the two pockets) and the polar and azimuthal angular dependence of the oscillation amplitudes. However, the requisite magnetic breakdown is possible only under the assumption that the horizontal mirror plane symmetry is spontaneously broken and that the bilayer tunneling, $t_\perp$, is substantially renormalized from its `bare' value. Under the assumption that $t_\perp= \tilde{Z}t_\perp^{(0)}$, where $\tilde{Z}$ is a measure of the quasiparticle weight, this suggests that $\tilde{Z} \lesssim 1/20$. Detailed comparisons with new YBa$_2$Cu$_3$O$_{6.58}$ QO data, taken over a very broad range of magnetic field, confirm specific predictions made by the breakdown scenario.