Image excitons and plasmon-exciton strong coupling in two-dimensional perovskite semiconductors

We present evidence for “image biexcitons” within organic-inorganic perovskite-coated silver gratings. These composite quasiparticles are formed by the interaction between an exciton and its image in the metal mirror below, with binding energy 100 meV at room temperature. By changing the polar and azimuthal angles of the incident light, we observe strong coupling between excitons and surface plasmon polaritons on the grating, with Rabi splittings of 150 and 125 meV for the exciton and biexciton, respectively. A detailed analysis of the field polarizations and dipole orientations shows how these Rabi couplings arise from the strongly compressed field volume.

Figure 1

(a) Schematic of the 2D lead iodide perovskite structure. (b) Absorption and photoluminescence spectra of the CHPI thin film on a glass substrate at room temperature. (c) SEM image (top) and AFM profile (bottom) of the Ag grating. (d) AFM image (top) and profile (bottom) of the CHPI-coated grating. (e) Schematic cross section of the CHPI-coated Ag grating structure.

Figure 2

Specular reflectivity scans at $\varphi =0^{\circ }$: CHPI-coated Ag grating with (a) TM and (b) TE polarized light, and (c) CHPI-coated 120 nm planar Ag film with TM polarized light. The electric field orientation is shown above each scan, and the positions of the exciton modes are indicated by arrows. (d) Change in emitted energy (top) and relative decay probabilities (bottom) of an exciton with energy 2.6 eV placed distance $l$ from the Ag surface. The dashed line indicates the experimentally measured redshift. (e) Schematic mechanism for SPP-mediated emission of the image biexciton.

Figure 3

TM polarized specular reflectivity of the CHPI-coated Ag grating, $D=417$ nm. White (“photonic” grating modes) and gray dashed lines (“plasmonic” grating modes) are guides, and exciton modes are indicated by black arrows. The exciton splitting increases with $\varphi$.

Figure 4

(a) Extracted spectral mode positions for $\varphi ={90}^{\circ }$ reflection dips (open circles), and fit from the three oscillator coupling model (dashed lines). (b), (c) Time-averaged $E$-field intensity profiles ($\vec{E}·\vec{E}$), as indicated. (d), (e) Simulated reflection spectra for (d) in-plane and (e) out-of-plane exciton dipoles.