Spin-orbit coupling and electron correlation effects on phonon anharmonicity of KOs2O6

Spin-orbit coupling and electron correlation effects from Os 5d electrons on phonon anharmonicity of β−pyrochlore superconductor KOs2O6 are systematically studied by first-principles frozen-phonon calculations. Spin-orbit coupling eliminates double-well potential, weakens imaginary frequency and enhances lattice stability. However, the gotten T2g and A1g asymmetrical modes show that the lattice is still instable. Then, the on-site Coulomb interaction as an important factor is considered, which completes with the spin-orbit coupling and makes greater influence on the anharmonicity. Therefore, KOs2O6 is a strong spin-orbit coupling and electronic correlation superconductor, and the multiple interactions have great effects on the anharmonicity, which may play an important role to the superconductivity of KOs2O6.