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1.
Nano Lett ; 20(3): 1676-1685, 2020 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-31995388

RESUMO

Exciton polaritons (EPs) are partial-light partial-matter quasiparticles in semiconductors demonstrating striking quantum phenomena such as Bose-Einstein condensation and single-photon nonlinearity. In these phenomena, the governing process is the EP relaxation into the ground states upon excitation, where various mechanisms are extensively investigated with thermodynamic limits. However, the relaxation process becomes drastically different and could significantly advance the understanding of EP dynamics for these quantum phenomena, when excited states of EPs are involved. Here, for the first time, we observe nonlinear optical responses at the EP excited states in a monolayer tungsten disulfide (WS2) microcavity, including dark excited states and dynamically metastable upper polariton bands. The nonlinear optics leads to unique emissions of ground states with prominent valley degree of freedom (DOF) via an anomalous relaxation process, which is applicable to a wide range of semiconductors from monolayer transition metal dichalcogenides (TMDs) to emerging halide perovskites. This work promises possible approaches to challenging experiments such as valley polariton condensation. Moreover, it also constructs a valley-dependent solid-state three-level system for terahertz photonics and stimulated Raman adiabatic passage.

2.
Proc Natl Acad Sci U S A ; 116(41): 20274-20279, 2019 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-31548414

RESUMO

The condensation of half-light half-matter exciton polaritons in semiconductor optical cavities is a striking example of macroscopic quantum coherence in a solid-state platform. Quantum coherence is possible only when there are strong interactions between the exciton polaritons provided by their excitonic constituents. Rydberg excitons with high principal value exhibit strong dipole-dipole interactions in cold atoms. However, polaritons with the excitonic constituent that is an excited state, namely Rydberg exciton polaritons (REPs), have not yet been experimentally observed. Here, we observe the formation of REPs in a single crystal CsPbBr3 perovskite cavity without any external fields. These polaritons exhibit strong nonlinear behavior that leads to a coherent polariton condensate with a prominent blue shift. Furthermore, the REPs in CsPbBr3 are highly anisotropic and have a large extinction ratio, arising from the perovskite's orthorhombic crystal structure. Our observation not only sheds light on the importance of many-body physics in coherent polariton systems involving higher-order excited states, but also paves the way for exploring these coherent interactions for solid-state quantum optical information processing.

3.
Proc Natl Acad Sci U S A ; 114(38): 10017-10022, 2017 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-28874560

RESUMO

Two-dimensional molecular aggregate (2DMA), a thin sheet of strongly interacting dipole molecules self-assembled at close distance on an ordered lattice, is a fascinating fluorescent material. It is distinctively different from the conventional (single or colloidal) dye molecules and quantum dots. In this paper, we verify that when a 2DMA is placed at a nanometric distance from a metallic substrate, the strong and coherent interaction between the dipoles inside the 2DMA dominates its fluorescent decay at a picosecond timescale. Our streak-camera lifetime measurement and interacting lattice-dipole calculation reveal that the metal-mediated dipole-dipole interaction shortens the fluorescent lifetime to about one-half and increases the energy dissipation rate by 10 times that expected from the noninteracting single-dipole picture. Our finding can enrich our understanding of nanoscale energy transfer in molecular excitonic systems and may designate a unique direction for developing fast and efficient optoelectronic devices.

4.
Phys Rev Lett ; 119(2): 027403, 2017 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-28753353

RESUMO

Monolayer transition metal dichalcogenides (TMD) with confined 2D Wannier-Mott excitons are intriguing for the fundamental study of strong light-matter interactions and the exploration of exciton polaritons at high temperatures. However, the research of 2D exciton polaritons has been hindered because the polaritons in these atomically thin semiconductors discovered so far can hardly support strong nonlinear interactions and quantum coherence due to uncontrollable polariton dynamics and weakened coherent coupling. In this work, we demonstrate, for the first time, a precisely controlled hybrid composition with angular dependence and dispersion-correlated polariton emission by tuning the polariton dispersion in TMD over a broad temperature range of 110-230 K in a single cavity. This tamed polariton emission is achieved by the realization of robust coherent exciton-photon coupling in monolayer tungsten disulphide (WS_{2}) with large splitting-to-linewidth ratios (>3.3). The unprecedented ability to manipulate the dispersion and correlated properties of TMD exciton polaritons at will offers new possibilities to explore important quantum phenomena such as inversionless lasing, Bose-Einstein condensation, and superfluidity.

5.
Nano Lett ; 16(3): 2004-10, 2016 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-26840127

RESUMO

Lasing in solution-processed nanomaterials has gained significant interest because of the potential for low-cost integrated photonic devices. Still, a key challenge is to utilize a comprehensive knowledge of the system's spectral and temporal dynamics to design low-threshold lasing devices. Here, we demonstrate intrinsic lasing (without external cavity) at low-threshold in an ultrathin film of coupled, highly crystalline nanospheres with overall thickness on the order of ∼λ/4. The cavity-free geometry consists of ∼35 nm zinc oxide nanospheres that collectively localize the in-plane emissive light fields while minimizing scattering losses, resulting in excitonic lasing with fluence thresholds at least an order of magnitude lower than previous UV-blue random and quantum-dot lasers (<75 µJ/cm(2)). Fluence-dependent effects, as quantified by subpicosecond transient spectroscopy, highlight the role of phonon-mediated processes in excitonic lasing. Subpicosecond evolution of distinct lasing modes, together with three-dimensional electromagnetic simulations, indicate a random lasing process, which is in violation of the commonly cited criteria of strong scattering from individual nanostructures and an optically thick sample. Subsequently, an electron-hole plasma mechanism is observed with increased fluence. These results suggest that coupled nanostructures with high crystallinity, fabricated by low-cost solution-processing methods, can function as viable building blocks for high-performance optoelectronics devices.


Assuntos
Nanosferas/química , Óxido de Zinco/química , Elétrons , Lasers , Luz , Nanosferas/ultraestrutura , Fônons , Temperatura Ambiente
6.
Phys Rev Lett ; 112(7): 076401, 2014 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-24579619

RESUMO

Hybrid organic-inorganic polaritons are formed by the simultaneous strong coupling of two degenerate excitons and a microcavity photon at room temperature. Wannier-Mott and Frenkel excitons in spatially separated ZnO and 3,4,7,8-napthalene tetracarboxylic dianhydride (NTCDA) layers, respectively, placed in a single Fabry-Perot microcavity contribute to the interaction with the cavity. A Rabi splitting of (322±8) meV between the upper and middle branches of the three branch polariton energy-momentum dispersion is observed. This is compared to only (224±22) meV and (218±8) meV Rabi splittings for NTCDA-only and ZnO-only reference cavities, respectively, and indicates that the excitonic component of the polariton is a Frenkel-Wannier-Mott hybrid. Unlike previous reports of hybrid polaritons, the mixing of the organic and inorganic eigenstates occurs independently of angle due to their energetic degeneracy, and can be tailored by adjusting the optical field distribution within the cavity.

7.
Opt Express ; 21(18): 20620-5, 2013 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-24103934

RESUMO

We report the formation of microcavity polaritons in a dielectric microcavity embedded with solution processed ZnO nanoparticles. Evidence of strong coupling between the excitons and cavity photons is demonstrated via anticrossing in the dispersion of the polariton states. At low temperatures (<150K), multiple polariton states arising due to coupling between different excitonic states and the cavity mode is observed. Rabi splitting of ~90 meV is shown to persist even at room temperature in the ZnO - dielectric microcavity.

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