Electric field-dependent phonon spectrum and heat conduction in ferroelectrics

This article shows experimentally that an external electric field affects the velocity of the longitudinal acoustic phonons (vLA), thermal conductivity (kappa), and diffusivity (D) in a bulk lead zirconium titanate-based ferroelectric. Phonon conduction dominates kappa, and the observations are due to changes in the phonon dispersion, not in the phonon scattering. This gives insight into the nature of the thermal fluctuations in ferroelectrics, namely, phonons labeled ferrons that carry heat and polarization. It also opens the way for phonon-based electrically driven all-solid-state heat switches, an enabling technology for solid-state heat engines. A quantitative theoret-ical model combining piezoelectric strain and phonon anharmonicity explains the field dependence of vLA, kappa, and D without any adjustable parameters, thus connecting thermodynamic equilibrium properties with trans-port properties. The effect is four times larger than previously reported effects, which were ascribed to field -dependent scattering of phonons.

Automated summary

This article experimentally demonstrates that an external electric field has an impact on the velocity of longitudinal acoustic phonons, thermal conductivity, and diffusivity in a bulk lead zirconium titanate-based ferroelectric. The changes observed are due to alterations in the phonon dispersion, not phonon scattering. This finding provides insights into the nature of thermal fluctuations in ferroelectrics and opens up possibilities for phonon-based all-solid-state heat switches, which are crucial for solid-state heat engines. A quantitative theoretical model combining piezoelectric strain and phonon anharmonicity explains the field dependence of these properties without any adjustable parameters, bridging the gap between thermodynamic equilibrium and transport properties. This effect is four times larger than previously reported effects attributed to field-dependent phonon scattering.