On the dynamical stability of copper-doped lead apatite

TL;DR

This study demonstrates that copper-doped lead apatite structures are dynamically stable at room temperature, resolving previous theoretical instability claims and aligning with experimental observations.

Contribution

The paper shows that anharmonic phonon interactions stabilize copper-doped lead apatite structures, reconciling theory with experimental stability reports.

Findings

Both parent and copper-doped structures are dynamically stable at room temperature.

Anharmonic phonon interactions are crucial for stabilizing certain phases.

Stability depends on volume and correlation strength, offering control over phase exploration.

Abstract

The recent claim of room temperature superconductivity in a copper-doped lead apatite compound, called LK-99, has sparked remarkable interest and controversy. Subsequent experiments have largely failed to reproduce the claimed superconductivity, while theoretical works have identified multiple key features including strong electronic correlation, structural instabilities, and dopability constraints. A puzzling claim of several recent theoretical studies is that both parent and copper-doped lead apatite structures are dynamically unstable at the harmonic level, questioning decades of experimental reports of the parent compound structures and the recently proposed copper-doped structures. In this work, we demonstrate that both parent and copper-doped lead apatite structures are dynamically stable at room temperature. Anharmonic phonon-phonon interactions play a key role in stabilizing some copper-doped phases, while most phases are largely stable even at the harmonic level. We also show that dynamical stability depends on both volume and correlation strength, suggesting controllable ways of exploring the copper-doped lead apatite structural phase diagram. Our results fully reconcile the theoretical description of the structures of both parent and copper-doped lead apatite with experiment.