Double-Cavity Modulation of Exciton Polaritons in CsPbBr₃ Microwire

Abstract

The lead halide perovskite has become a promising candidate for the study of exciton polaritons due to their excellent optical properties. Here, both experimental and simulated results confirm the existence of two kinds of Fabry−Peŕot microcavities in a single CsPbBr 3 microwire with an isosceles right triangle cross section, and we experimentally demonstrate that confined photons in a straight and a folded Fabry−Peŕot microcavity are strongly coupled with excitons to form exciton polaritons. Furthermore, we reveal the polarization characteristic and double-cavity modulation of exciton polaritons emission by polarization-resolved fluorescence spectroscopy. Our results not only prove that the modulation of exciton polaritons emission can occur in this simple double-cavity system but also provide a possibility to develop related polariton devices.

Single-Mode Surface-Emitting Polariton Lasing with Switchable Polarization in a CsPbBr3 Microwire Folded Fabry–Pérot Cavity

“…Similarly, the same conclusion was obtained in the other CsPbBr 3 microwire with W ∼ 2.8 and 5.3 μm (Supporting Information, Figure S4). The E – k ⊥ dispersion relationship of polaritons is obtained by using the dielectric function model, as shown in Figure d (Supporting Notes of the Supporting Information, the E – k ⊥ dispersion of polaritons). ,,, The Rabi splitting energy ( ℏ Ω) of the U-cavity polaritons is about 60 meV higher than that of the V-cavity polaritons, which may be related to the oscillator strength and the mode volume (Supporting Information, Figure S5). − …”

“…From the RE spectra in Figure S7, it can be similarly concluded that the ΔE increases gradually with the decrease of the W. Figure 2c,d shows the linear relationship between ΔE and 1/W at the dashed lines in Figure 2a,b, respectively, which demonstrates that resonators are created along the light propagation channels shown as the arrows in Figure 1a,b. According to the group refractive index 27,32 n g = hc/(2LΔE), where L is the effective length of the resonator (i.e., the W or the S). When the energy falls from 2.330 to 2.270 eV, the n g of the V-cavity reduces from 7.4 to 4.3, and the n g of the U-cavity decreases from 10.3 to 7.7.…”

“…When the resonant route is fixed, the n g at each energy is independent of the W, similar to the fact that Rabi splitting is relatively insensitive to cavity length in this cavity size range. 27,43,44 The difference of the n g between U-cavity and V-cavity can be affected by the crystal anisotropy and the effective mode volume. 36,45−47 Therefore, both the E− k ⊥ dispersion relation and the slow-light effect prove the existence of two folded F−P microcavity exciton polaritons.…”

“…In addition, the strong coupling between light and matter (i.e., exciton polaritons) is indicated by the unequal spacings of cavity modes shown in the spectra. 23,24,27 Unequal spacings of cavity modes in the PL (or 2nd-PL) spectra are observed both in the U-cavity and the V-cavity. However, the ratio of the mode spacing (the shaded area in Figure 1c) between the two cavities is not strictly proportional to the cavity length ratio (i.e., W U-cavity /S V-cavity ∼ √2), which indicates that the coupling strength of excitons and photons in the two microcavities is different.…”

“…Exciton polaritons are bosonic quasiparticles generated through the strong coupling of confined photons and excitons within a microcavity. − Exciton–polariton lasers with a lower threshold have been extensively investigated in recent years because they are not limited by particle population inversion like conventional lasers. − All-inorganic lead halide perovskites (CsPbX 3 , X = Cl, Br, I) are promising materials for polariton lasing devices owing to their large exciton binding energy, high oscillation strength, large absorption coefficient, high quantum efficiency, and easy-to-band gap engineering. Notably, many of these materials possess natural micro/nanostructures that facilitate resonant cavity conditions for polariton laser generation, − offering a novel avenue toward the compactness and integrability of polaritonic devices. However, there are few works about single-mode polariton lasers with switchable output and surface-emitting in such natural microcavities.…”