In 1951, Huang firstly proposed the concept of polariton and derived its dispersion relation by combing lattice vibration in ionic crystals with electromagnetic waves using classic electromagnetic theory, which was primarily aimed to explain light retardation effect (see Fig. 1)[1]. Hopfield et al. extended Huang’s theory to exciton−photon interaction in crystals, experimentally demonstrated Raman scattering by phonon polaritons and formally proposed the name of “polariton” from “polarization” and “photon”[2, 3]. Since then, polariton has been widely studied in fundamental and application research fields.
Figure 1. The principle of the interaction between photons and lattice vibration.
Polariton is half-matter, half-light quasi-particle that forms when the energy transfer rate between polarized particles in matter (e.g. exciton, phonon, plasmon, magneton) and photons is faster than their dissipative rate. Inheriting from the matter which is massive and controllable as well as the photon which is massless and inactive, polariton exhibits a light mass and interactive behavior, and hence creates an idea platform to explore quantum electromagnetic dynamics in solid-state matters and develop high-speed, low-loss devices.
With revolution and rapid advances in semiconductor and microfabrication technologies, exciton–polariton (EP) has aroused great attentions from worldwide scientists in particular when Bose–Einstein condensation (BEC) of EP was realized in GaAs and CdTe quantum wells under optical pump in 2000s[4, 5]. Researchers consider that the EP–BECs make photons controllable by slowing their velocity, and hence could be applicable to develop optical chips with higher computing speed and lower energy consumption in comparison to electronic devices. Considerable efforts have been made, and till so far room temperature EPs have been realized in a variety of inorganic and organic semiconductors[6−9]. Moreover, electrically-driven BECs from InGaAs and EPs from organic semiconductors compound, such as 9,10-bis(phenylethynyl)anthracene, have been achieved at room temperature[10, 11]. Very recently, photo-transistors applying EP–BECs have been established, and new concepts such as parity-time-symmetry are introduced to extend the capability of light manipulation as well as lower threshold of semiconductor lasers[12−14].
To date, on the one hand, the research in EPs of these well-established semiconductors is still blooming, and continuous efforts are devoted to push laboratory devices to industry-friendly products. The central issues include low consumption, reliability and mass fabrication, etc. On the other hand, this area grows rapidly with the emergence of new materials including two dimensional semiconductors and metallic halide perovskites, etc.[15−21]. The perovskites combine the advantages of inorganic and organic semiconductors, exhibiting high exciton oscillator strength, long-range bipolar carrier transport, high defect tolerance, easy-tuning of band gap as well as low-cost fabrication processes[22−24]. In the last few years, several groups from Singapore, China and U.S.A. have reported EPs and EP−BEC effects at room temperature as well as continuous wave pumped EP lasing from the perovskite family[15−18, 25]. Despite of structure instability, perovskite raises the possibility to develop flexible, low cost, and low energy consumption EP devices.
References
[1] Huang K. Lattice vibrations and optical waves in ionic crystals. Nature, 1951, 167, 779
[2] Henry C, Hopfield J. Raman scattering by polaritons. Phys Rev Lett, 1965, 15, 964
[3] Hopfield J. Theory of the contribution of excitons to the complex dielectric constant of crystals. Phys Rev, 1958, 112, 1555
[4] Kasprzak J, Richard M, Kundermann S, et al. Bose–Einstein condensation of exciton polaritons. Nature, 2006, 443, 409
[5] Deng H, Weihs G, Santori C, et al. Condensation of semiconductor microcavity exciton polaritons. Science, 2002, 298, 199
[6] Christopoulos S, Von Högersthal G B H, Grundy A, et al. Room-temperature polariton lasing in semiconductor microcavities. Phys Rev Lett, 2007, 98, 126405
[7] Byrnes T, Kim N Y, Yamamoto Y. Exciton–polariton condensates. Nat Phys, 2014, 10, 803
[8] Kéna-Cohen S, Forrest S. Room-temperature polariton lasing in an organic single-crystal microcavity. Nat Photon, 2010, 4, 37
[9] Plumhof J D, Stöferle T, Mai L, et al. Room-temperature Bose–Einstein condensation of cavity exciton-polaritons in a polymer. Nat Mater, 2013, 13, 247
[10] Schneider C, Rahimi-Iman A, Kim N Y, et al. An electrically pumped polariton laser. Nature, 2013, 497, 348
[11] Cui Q H, Peng Q, Luo Y, et al. Asymmetric photon transport in organic semiconductor nanowires through electrically controlled exciton diffusion. Sci Adv, 2018, 4, eaap9861
[12] Ballarini D, De Giorgi M, Cancellieri E, et al. All-optical polariton transistor. Nat Commun, 2013, 4, 1778
[13] Gao T, Eldridge P S, Liew T C H, et al. Polariton condensate transistor switch. Phys Rev B, 2012, 85, 235102
[14] Lien J Y, Chen Y N, Ishida N, et al. Multistability and condensation of exciton–polaritons below threshold. Phys Rev B, 2015, 91, 024511
[15] Evans T J, Schlaus A, Fu Y, et al. Continuous-wave lasing in cesium lead bromide perovskite nanowires. Adv Opt Mater, 2018, 6, 1700982
[16] Su R, Diederichs C, Wang J, et al. Room-temperature polariton lasing in all-inorganic perovskite nanoplatelets. Nano Lett, 2017, 17, 3982
[17] Zhang S, Shang Q, Du W, et al. Strong exciton–photon coupling in hybrid inorganic–organic perovskite micro/nanowires. Adv Opt Mater, 2018, 6, 1701032
[18] Shang Q, Zhang S, Liu Z, et al. Surface plasmon enhanced strong exciton–photon coupling in hybrid inorganic–organic perovskite nanowires. Nano Lett, 2018, 18, 3335
[19] Dufferwiel S, Schwarz S, Withers F, et al. Exciton–polaritons in van der Waals heterostructures embedded in tunable microcavities. Nat Commun, 2015, 6, 8579
[20] Lundt N, Klembt S, Cherotchenko E, et al. Room-temperature Tamm-plasmon exciton-polaritons with a WSe2 monolayer. Nat Commun, 2016, 7, 13328
[21] Low T, Chaves A, Caldwell J D, et al. Polaritons in layered two-dimensional materials. Nat Mater, 2017, 16, 182
[22] Stranks S D, Snaith H J. Metal-halide perovskites for photovoltaic and light-emitting devices. Nat Nanotech, 2015, 10, 391
[23] Sutherland B R, Sargent E H. Perovskite photonic sources. Nat Photon, 2016, 10, 295
[24] Zhang Q, Su R, Du W, et al. Advances in small perovskite-based lasers. Small Methods, 2017, 1, 1700163
[25] Fieramosca A, Polimeno L, Ardizzone V, et al. Two-dimensional hybrid perovskites sustaining strong polariton interactions at room temperature. Sci Adv, 2019, 5, eaav9967
