Near-Field Radiative Energy Transfer Between Two Spheres

Radiative energy transfer between closely spaced bodies is known to be significantly larger than that predicted by classical radiative transfer because of tunneling due to evanescent waves. Polar materials like silicon carbide and silica can support surface phonon polaritons due to resonances in the dielectric function of such materials. This leads to an enhanced density of states of electromagnetic surface modes near the surface compared to vacuum and leads to a pronounced increase in energy transfer near the resonance region. Experimental measurements between half-planes of polar materials can be very challenging because of the difficulty in measuring the gap as well as the parallelism between the surfaces. Theoretical investigation of near-field energy transfer on the other hand, is generally restricted to that between two parallel half-planes because of the complications involved in analyzing other configurations such as sphere-sphere or sphere-plane. Sphere-sphere or sphere-plane configurations beyond the dipole approximation have not been attempted. In this work, we analyze numerically the radiative energy transfer between two adjacent non-overlapping spheres.