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Colloidal lead halide perovskite (LHP) nanocrystals are of interest as photoluminescent quantum dots (QDs) whose properties depend on the size and shape. They are normally synthesized on subsecond time scales through hard-to-control ionic metathesis reactions. We report a room-temperature synthesis of monodisperse, isolable spheroidal APbBr3 QDs (A=Cs, formamidinium, methylammonium) that are size-tunable from 3 to over 13 nanometers. The kinetics of both nucleation and growth are temporally separated and drastically slowed down by the intricate equilibrium between the precursor (PbBr2) and the A[PbBr3] solute, with the latter serving as a monomer. QDs of all these compositions exhibit up to four excitonic transitions in their linear absorption spectra, and we demonstrate that the size-dependent confinement energy for all transitions is independent of the A-site cation.
A condensed-matter platform for analog simulation of complex two-dimensional molecular bonding configurations, based on optically trapped exciton-polariton condensates is proposed. The stable occupation of polariton condensates in the excited states of their optically configurable potential traps permits emulation of excited atomic orbitals. A classical mean-field model describing the dissipative coupling mechanism between p-orbital condensates is derived, identifying lowest-threshold condensation solutions as a function of trap parameters corresponding to bound and antibound π and σ bonding configurations, similar to those in quantum chemistry.
Attaining pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging. The past 20 years have seen the development of several solid-state quantum emitters, but most of them require highly sophisticated techniques (e.g., ultrahigh vacuum growth methods and cryostats for low-temperature operation). The system complexity may be significantly reduced by employing quantum emitters capable of working at room temperature. Here, we present a systematic study across ∼170 photostable single CsPbX3 (X: Br and I) colloidal quantum dots (QDs) of different sizes and compositions, unveiling that increasing quantum confinement is an effective strategy for maximizing single-photon purity due to the suppressed biexciton quantum yield. Leveraging the latter, we achieve 98% single-photon purity (g(2)(0) as low as 2%) from a cavity-free, nonresonantly excited single 6.6 nm CsPbI3 QDs, showcasing the great potential of CsPbX3 QDs as room-temperature highly pure single-photon sources for quantum technologies.
Semiconductor quantum dots have long been considered artificial atoms, but despite the overarching analogies in the strong energy-level quantization and the single-photon emission capability, their emission spectrum is far broader than typical atomic emission lines. Here, by using ab-initio molecular dynamics for simulating exciton-surface-phonon interactions in structurally dynamic CsPbBr3 quantum dots, followed by single quantum dot optical spectroscopy, we demonstrate that emission line-broadening in these quantum dots is primarily governed by the coupling of excitons to low-energy surface phonons. Mild adjustments of the surface chemical composition allow for attaining much smaller emission linewidths of 35−65 meV (vs. initial values of 70–120 meV), which are on par with the best values known for structurally rigid, colloidal II-VI quantum dots (20−60 meV). Ultra-narrow emission at room-temperature is desired for conventional light-emitting devices and paramount for emerging quantum light sources.
Lead-halide perovskite APbX3 (A=Cs or organic cation; X=Cl, Br, I) quantum dots (QDs) are subject of intense research due to their exceptional properties as both classical 1 and quantum light sources. Here, we report a comprehensive investigation of the room temperature single QD optical properties. The results reveal the origin of the QD homogeneous PL linewidths, and the peculiar size-dependent exciton photoluminescence line broadening and the exciton and multi-excitons recombination dynamics. Experimental results are corroborated by ab-initio molecular dynamics. Such findings guide the further design of robust single photon sources operating at room temperature.En savoir plus
A new synthetic method for colloidal perovskite nanocrystals has been designed, which offers slow thermodynamic control instead of conventional kinetic growth. The reaction time is increased up to 30 minutes while a wide size range of nanoparticles, some even reaching the strong confinement regime, is obtained with high level control of size and shape. The synthesized quantum dots (QDs) turn out to have a spheroidal shape on average with remarkably well-separated higher absorption peaks. For the first time, this allows for a direct comparison between theory and experimental data related to the transitions beyond the lowest absorption line. Using empirical modelling with second-order many body perturbation theory, we are able to predict the energy positions as well as the oscillator strength of not only the lowest 1s-1s exciton but also of the higher excitonic transitions. The calculated values are in fair agreement with the experimental data. Besides, by taking into consideration the spherical and cuboidal confining potentials, our theory offers an explanation for the well-defined higher transitions in the spheroidal QDs compared to cuboidal ones obtaining from more standard synthetic approaches. The accuracy of the theoretical methods will be also critically discussed.En savoir plus
Lead-halide perovskite APbX3 (A=Cs or organic cation; X=Cl, Br, I) quantum dots (QDs) are subject of intense research due to their exceptional properties as both classical 1 and quantum light sources. Here we present perovskite-type (ABO3) binary nanocrystal superlattices, created via the shape-directed co-assembly of steric-stabilized, highly luminescent cubic CsPbBr 3 nanocrystals (which occupy the B and/or O lattice sites), assembled in combination with spherical Fe 3O4 or NaGdF4 nanocrystals (A sites). These ABO3 superlattices, as well as the binary NaCl and AlB 2 superlattice structures that we demonstrated, exhibit a high degree of orientational ordering of the CsPbBr 3 nanocubes which preserve their high oscillator strength and long exciton coherence time in the assembly. Such superlattices exhibit superfluorescence—a collective emission that results in a burst of photons with ultrafast radiative decay (22 picoseconds) that could be tailored, by structural engineering of the nanoparticle assembly, for use in ultrabright (quantum) light sources. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures.En savoir plus
Perovskite nanocrystals (NCs) are among the most fashionable names nowadays in the field of colloidal synthesis owing to their superior photoluminescence quantum yield and blinking-free properties, which make them promising materials for both classical and quantum light sources. Their brightness and sub-nanosecond radiative decay originates from the inherent correlation effects. The many-body Coulomb interaction has generally been studied for semiconductor quantum dots. Perovskites, as a consequence of the unique properties of their dielectric functions, possess enhanced Coulomb interaction between the charge carriers. This leads to large binding energies of multi-exciton systems such as trion and biexciton in these NCs or the sizable splitting in the fine structure of single exciton states. Considering each NC as an artificial atom under the envelope function approximation, this problem of correlation effects can be approached at first by using second-order many-body techniques. This offers an elegant and efficient method that provides qualitative results for the trion and biexciton binding energies. In going beyond the second-order description, configuration interaction can be employed to include the correlation energies between the various charge carriers in a more holistic manner.En savoir plus
Multicomponent Bose–Einstein condensates, quantum Hall systems, and chiral magnetic materials display twists and knots in the continuous symmetries of their order parameters known as skyrmions. Originally discovered as solutions to the nonlinear sigma model in quantum field theory, these vectorial excitations are quantified by a topological winding number dictating their interactions and global properties of the host system. Here, we report the experimental observation of a stable individual second-order meron and antimeron appearing in an electromagnetic field. We realize these complex textures by confining light into a liquid-crystal-filled cavity that, through its anisotropic refractive index, provides an adjustable artificial photonic gauge field that couples the cavity photon motion to its polarization, resulting in the formation of these fundamental vectorial vortex states of light. Our observations could help bring topologically robust room-temperature optical vector textures into the field of photonic information processing and storage.
We investigate a photonic device consisting of two coupled optical cavities possessing Rashba-Dresselhaus spin-orbit coupling, TE-TM splitting, and linear polarization splitting that opens a tunable energy gap at the diabolic points of the photon dispersion; giving rise to an actively addressable local Berry curvature. The proposed architecture stems from recent advancements in the design of artificial photonic gauge fields in liquid crystal cavities [K. Rechcinska et al., Science 366, 727 (2019)]. Our study opens perspectives for topological photonics, room-temperature spinoptronics, and studies on the quantum geometrical structure of photonic bands in extreme settings.