Title: Relative merits of Phononics vs. Plasmonics: the energy balance approach,
Abstract: The common feature of various plasmonic schemes is their ability to confine
optical fields of surface plasmon polaritons (SPPs) into sub-wavelength volumes
and thus achieve a large enhancement of linear and nonlinear optical
properties. This ability, however, is severely limited by the large ohmic loss
inherent to even the best of metals. However, in the mid and far infrared
ranges of the spectrum there exists a viable alternative to metals, polar
dielectrics and semiconductors in which dielectric permittivity (the real part)
turns negative in the Reststrahlen region. This feature engenders the so-called
surface phonon polaritons (SPhPs) capable of confining the field in a way akin
to their plasmonic analogues, the SPPs. Since the damping rate of polar phonons
is substantially less than that of free electrons, it is not unreasonable to
expect that phononic devices may outperform their plasmonic counterparts. Yet a
more rigorous analysis of the comparative merits of phononics and plasmonics
reveals a more nuanced answer, namely that while phononic schemes do exhibit
narrower resonances and can achieve a very high degree of energy concentration,
most of the energy is contained in the form of lattice vibrations so that
enhancement of the electric field, and hence the Purcell factor, is rather
small compared to what can be achieved with metal nanoantennas. Still, the
sheer narrowness of phononic resonances is expected to make phononics viable in
applications where frequency selectivity is important.