Critical role of magnetic moments on lattice dynamics in YBa${}_{2}$Cu${}_{3}$O${}_{6}$

TL;DR

This study uses an advanced density functional to accurately model the lattice dynamics and magnetic interactions in YBa₂Cu₃O₆, revealing significant magnetoelastic coupling that impacts phonon behavior relevant to high-temperature superconductivity.

Contribution

It provides the first accurate first-principles description of combined electronic, magnetic, and lattice degrees of freedom in YBa₂Cu₃O₆, highlighting the importance of magnetic moments in lattice dynamics.

Findings

Reproduces experimental phonon dispersion accurately

Identifies strong magnetoelastic coupling in Cu-O bond stretching modes

Shows magnetic state improves phonon predictions over non-magnetic models

Abstract

The role of lattice dynamics in unconventional high-temperature superconductivity is still vigorously debated. Theoretical insights into this problem have long been prevented by the absence of an accurate first-principles description of the combined electronic, magnetic, and lattice degrees of freedom. Utilizing the recently constructed r$^2$SCAN density functional that stabilizes the antiferromagnetic (AFM) state of the pristine oxide YBa$_2$Cu$_3$O$_6$, we faithfully reproduce the experimental dispersion of key phonon modes. We further find significant magnetoelastic coupling in numerous high energy Cu-O bond stretching optical branches, where the AFM results improve over the soft non-magnetic phonon bands.