Excitation protocols for non-linear phononics in bismuth and antimony

TL;DR

This paper investigates the optical control of coherent phonons in bismuth and antimony, revealing the impact of anharmonicity on phonon manipulation and proposing a new linearization protocol for enhanced control in non-linear phononics.

Contribution

It introduces a linearization protocol to extend phonon control techniques to anharmonic, broken-symmetry materials, supported by a first-principles based theoretical framework.

Findings

Phonons with strong optomechanical coupling exhibit high anharmonicity.

Anharmonicity causes light-induced phonon softening, affecting standard protocols.

The proposed linearization protocol improves control at high displacement amplitudes.

Abstract

We study the optical generation and control of coherent phonons in elemental bismuth (Bi) and antimony (Sb) using a classical equation of motion informed by first-principles calculations of the potential energy surface and the frequency-dependent macroscopic dielectric function along the zone-centered optical phonons coordinates. Using this approach, we demonstrate that phonons with the largest optomechanical couplings, also have the strongest degree of anharmonicity among the zone-centered modes, a result of the broken symmetry structural ground state of Bi and Sb. We show how this anharmonicity, explaining the light-induced phonon softening observed in experiments, prevents the application of standard phonon-amplification and annihilation protocols. We introduce a simple linearization protocol that extends the use of such protocols to the case of anharmonic phonons in broken symmetry materials, and demonstrate its efficiency at high displacement amplitudes. Our formalism and results provide a path for improving optical control in non-linear phononics.