Long-Range Mid-Infrared Energy Transfer Mediated by Hyperbolic Phonon Polaritons.

We provide a framework to theoretically describe long-range energy transfer in single and twisted two-dimensional hyperbolic slabs. We demonstrate that phonon polaritons, quantum superpositions of photons and lattice vibrations in polar dielectrics, can mediate and enhance energy transfer at ranges far exceeding those of conventional mid-infrared (MIR) platforms and with extreme directionality. This is because the dipole-dipole interaction potential energy diverges along the asymptotes of the real-space hyperbolic opening angle. Our findings allow us to extend classical and quantum interactions between dipoles, typically strictly confined to the near-field, beyond several free-space MIR wavelengths. We use α-MoO3 as a representative material, but this mechanism could be extended to other anisotropic media beyond the MIR.