Optically trapped exciton-polariton condensates in a perovskite microcavity

TL;DR

Realizing room-temperature, optically trapped exciton-polariton condensates in robust perovskite materials addresses the need for scalable, nonlinear light sources. The authors fabricate CsPbBr$_{3}$ microwire microcavities embedded in distributed Bragg reflectors and employ a ring-shaped nonresonant pump to create an optically induced trap, yielding a polariton potential $V(r) ∝ n_X(r)$ that confines condensates into high-order angular states up to $l=19$ on the 2V branch. The condensates switch between whispering-gallery like petal modes and ripple Hermite-Gaussian states as trap width and pump power are varied, with spatial profiles well described by a 2D harmonic confinement model: $ ho(oldsymbol{r}) = |\,oldsymbol{ abla}|ψ_{-l} + ψ_l|^2$ and $ψ_l(oldsymbol{r},oldsymbol{φ}) = rac{eta}{\\sqrt{2 \\pi l!}} e^{i l φ} (β r)^l e^{-β^2 r^2/2}$. This work demonstrates room-temperature, reconfigurable, structured light generation and points toward applications in nonlinear photonics, optical switching, and potential polariton-based quantum simulators.

Abstract

We demonstrate room temperature optical trapping and generation of high-order angular harmonics in exciton-polariton condensates in a monocrystalline CsPbBr$_3$ perovskite-filled microcavity. Using an annular nonresonant excitation profile focused onto the perovskite, we observed power-driven switching between different transverse modes of the optically induced trap. We explore the interplay between the perovskite crystal dimensions and the optical trap diameter that allows the condensate to transition from whispering gallery-like petal shapes to extended ripple states. Our results underline the feasibility in creating high-order quantum states in perovskite polariton condensates for reconfigurable and structured room temperature nonlinear lasing.

Figures (6)

• Figure 1: Sample preparation process. a Dripping the prepared solution in PDMS template of predefined diameter and height prepared on the 6.5 pairs of SiO$_{2}$/TiO$_{2}$ DBRs' substrate. b Monocrystalline CsPbBr$_3$ microwire growth by microfluidic-assisted crystallization. c The low-temperature PECVD technique covering with 10.5 pairs of Si$_{3}$N$_{4}$/SiO$_{2}$ DBRs to obtain microcavity confinement with a photon stopband centered at 535 nm.
• Figure 2: Experiment preparation and principal measurments. a A scheme of the experimental setup composed of beamsplitter (BS), objective (O), mirrors (M), lenses (L) and Fourier lenses (FL). The inset illustrates schematically the optical trap and the sample. Panel b shows the prepared annular laser beam profile focused on the sample and panel c the corresponding luminescence below threshold. The dashed circular lines help to demonstrate, as a guide-to-the-eyes, that the hot exciton reservoir is created within the pump profile. Panel d shows the angle resolved PL of the system below threshold, revealing two pairs of H-V (red and green curve) split polariton branches. The dashed lines are parabolic fits to the data using Eqs. \ref{['polaritondisspertion']}. The data is presented in respect to the $\sin \theta$ (where $\theta$ is the angle at which the photoluminescence signal was collected in the experiment and $k=E \sin \theta / hc$, where $E$ is the polariton energy). Panel e demonstrates the power-dependent integrated emission intensity (red curve, arrow to the left Y-axis) and corresponding blueshift of the condensate emission line (blue curve, arrow to the right Y-axis) in units of condensation threshold power $P_\text{th}$.
• Figure 3: Optically trapped polariton condensate harmonics of varying angular momentum $l$. All results are resolved in V-polarization and pumped $\approx10\%$ above condensation threshold. The pump is centered on the microwire which is much broader. Panels a-d show the experiment, and e-h show corresponding theoretical profiles from \ref{['eq.rho']}. Condensates petals formed by ring-shaped exciton reservoirs of the spatial distribution described by \ref{['realringpotential']} with radius $R = 3.5$$\mu$m and different thickness parameters $\sigma$ for each panel, i.e. a: $\sigma \approx 1.5$$\mu m$, b: $\sigma = 1.3$$\mu$m; c: $\sigma = 0.9$$\mu$m; d: $\sigma = 0.6$$\mu$m.
• Figure 4: Panel (a) shows the emission at threshold for a configuration in which the trap (blue dots) is larger than the wire diameter (black dashed lines). The bright emission around $x = -2.5 \,\mu\text{m}$ is attributed to a sample defect. Panel (b) depicts the emission above (20%) threshold, and panel (c) presents real-space spectra acquired under the same conditions as in (b), with the locations indicated by black lines. The eight trapped nodes of the condensate in panel (a) are associated with modes in the spectrum that are symmetrically distributed in the dispersion [see panel 4(c)] in the vicinity of energies $2.278 \,\text{eV}$ and $2.268 \,\text{eV}$, whereas the remaining observed modes, which are asymmetrically distributed around $2.304 \,\text{eV}$ and $2.264 \,\text{eV}$, are related to condensation at the defect visible in panel (a) at $x = -2.5 \,\mu\text{m}$ and $y = 1.5 \,\mu\text{m}$. Panel (d) shows a cross section through two states visible around $2.278 \,\text{eV}$.
• Figure 5: Tunability of mode number by pump power. Panels a and b shows real space images of trapped condensate at 1.1 and 1.4 P$_{th}$ using an asymmetric trap profile as indicated with blue dashed circle, respectively, c and d are cross-sections of a and b at $y = 0$ as indicated by dashed lines. Panel e show power-scan of the ripples number and black dotted lines are to guide the eye. The angle-resolved spectra of the condensates for pumping powers as in a and b are visible on f and g. Condensate ripples formed by ring-shape exciton reservoir described by \ref{['realringpotential']} with parameters: $R = 3.5$$\mu$m, $\sigma = 1.5$$\mu$m