In
physics, polaritons/pəˈlærɪtɒnz,poʊ-/[1] are
quasiparticles resulting from strong coupling of
electromagnetic waves with an electric or magnetic
dipole-carrying excitation.[example needed] They are an expression of the common
quantum phenomenon known as
level repulsion, also known as the
avoided crossing principle. Polaritons describe the crossing of the
dispersion of light with any interacting
resonance. To this extent polaritons can also be thought of as the new
normal modes of a given material or structure arising from the strong coupling of the bare modes, which are the photon and the dipolar oscillation. The polariton is a
bosonic quasiparticle, and should not be confused with the
polaron (a
fermionic quasiparticle), which is an electron plus an attached
phonon cloud.
Whenever the polariton picture is valid (i.e., when the weak coupling limit is an invalid approximation), the model of photons propagating freely in crystals is insufficient. A major feature of polaritons is a strong dependency of the propagation speed of light through the crystal on the
frequency of the photon. For exciton-polaritons, a wealth of experimental results on various aspects have been gained in the case of
copper(I) oxide.
History
Oscillations in ionized gases were observed by
Lewi Tonks and
Irving Langmuir in 1929.[2] Polaritons were first considered theoretically by
Kirill Borisovich Tolpygo.[3][4] They were termed light-excitons in Soviet scientific literature. That name was suggested by
Solomon Isaakovich Pekar, but the term polariton, proposed by
John Hopfield, was adopted. Coupled states of electromagnetic waves and phonons in ionic crystals and their dispersion relation, now known as phonon polaritons, were obtained by Tolpygo in 1950[3][4] and, independently, by
Huang Kun in 1951.[5][6] Collective interactions were published by
David Pines and
David Bohm in 1952, and
plasmons were described in silver by
Herbert Fröhlich and H. Pelzer in 1955. R.H Ritchie predicted surface plasmons in 1957, then Ritchie and H.B. Eldridge published experiments and predictions of emitted photons from irradiated metal foils in 1962. Otto first published on surface plasmon-polaritons in 1968.[7]
Room-temperature superfluidity of polaritons was observed[8] in 2016 by Giovanni Lerario et al., at
CNR NANOTEC Institute of Nanotechnology, using an organic microcavity supporting stable
Frenkel exciton-polaritons at room temperature. In February 2018, scientists reported the discovery of a new three-photon form of
light, which may involve polaritons, that could be useful in the development of
quantum computers.[9][10]
Types
A polariton is the result of the combination of a
photon with a polar excitation in a material. The following are types of polaritons:
^
abTolpygo, K.B. (1950). "Physical properties of a rock salt lattice made up of deformable ions". Zhurnal Eksperimentalnoi I Teoreticheskoi Fiziki (J. Exp. Theor. Phys.). 20 (6): 497–509, in Russian.
^
abK.B. Tolpygo, "Physical properties of a rock salt lattice made up of deformable ions", Zh. Eks.Teor. Fiz. vol. 20, No. 6, pp. 497–509 (1950), English translation: Ukrainian Journal of Physics, vol. 53, special issue (2008);
"Archived copy"(PDF). Archived from
the original(PDF) on 2015-12-08. Retrieved 2015-10-15.{{
cite web}}: CS1 maint: archived copy as title (
link)