Phonon-assisted Casimir interactions: the case of piezoelectric materials

The strong coupling between electromagnetic field and lattice oscillation in piezoelectric materials gives rise to phonon polariton excitations. The coupling between such quasiparticles and the electromagnetic field opens up new directions to modulate the ubiquitous Casimir force. Here by utilizing the generalized Born-Huang hydrodynamics model, three types of phonons in piezoelectrics are studied: longitudinal optical phonon, transverse optical phonon and interface phonon polariton [1]. As a result of the coupling between these phonons and the electromagnetic field, the electromagnetic and elastic boundary conditions result in a complex set of Fresnel reflection matrices which prevents the utilization of the standard Lifshitz approach for calculating Casimir forces in the imaginary frequency domain. Our calculations are based on an approach within real frequency and finite temperatures [2], through which various regimes of the Casimir interactions are examined. Our study shows that piezoelectrics emerge as a set of materials where the ubiquitous Casimir force can be controlled via phonon properties for the first time.

[1] B. K. Ridley, Phys. Rev. B 49, 17253 (1994).

[2] V. B. Svetovoy, Phys. Rev. A 76, 062102 (2007)