Condensed Matter/Materials & Biological Physics Seminar with Joshua Caldwell on Polaritonic Media

The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. In the infrared, this requires compression of the wavelength to length scales well below that of the free-space values.  While traditional dielectric materials do not exhibit indices of refraction high enough in non-dispersive media to realize such compression, the implementation of polaritons, quasi-particles comprised of oscillating charges and photons, enable such opportunities. Two predominant forms of polaritons, the plasmon and phonon polariton, which are derived from light coupled with free carriers or polar optic phonons, respectively, are broadly applied in the mid- to long-wave infrared. However, the short scattering lifetimes of free-carriers results in high losses and broad linewidths for the former, while the fast dispersion and narrow band of operation for the latter result in significant limitations for both forms.

Here we will discuss the opportunity to implement polaritonic strong coupling between different media in an effort to dictate the polaritonic dispersion relation, and thus, the propagation and resonant properties of these materials. Further, by employing the extreme anisotropy of crystals ranging from two-dimensional materials such as hexagonal boron nitride and transition metal dichalcogenides to low-symmetry monoclinic to triclinic materials, novel optical phenomena such as hyperbolicity and shear polaritons are observed. The talk will highlight ultra-strong coupling between both forms of polaritons in the context of infrared emitters, as a means to control planar propagation using hyperbolic polaritons, and modifying thermal dissipation at ultrafast time scales.