Xiaoze Liu

Strong light–matter coupling in two-dimensional atomic crystals

Microcavity polaritons—the bosonic quasiparticles that result from strong light–matter coupling—are observed for the first time in a dielectric cavity containing a monolayer of molybdenum disulphide at room temperature.

Formation of microcavity polaritons in ZnO nanoparticles.

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.

Synthesis and Application of Monolayer Semiconductors (June 2015)

Recently, semiconducting monolayers, such as MoS2 and WSe2, have been highlighted for their spin-valley coupling, diverse band structures, bendability, and excellent optoelectronic performances. With a subnanometer thickness of atomic layers, the transition metal dichalcogenides (TMDc) atomic layers demonstrate a significant photoresponse, considerable absorption to incident sunlight and favorable transport performances, leading to applications in the electronic circuit requiring low stand-by power, diverse optoelectronic devices, and next-generation nanoelectronics. Therefore, the class of monolayer TMDc offers a burgeoning field in materials science, fundamental physics, and optoelectronics. A feasible synthetic process to realize controlled synthesis of large area and high quality of TMDc monolayers is in demands. In this review, we will introduce the progress on synthesis and applications of the TMDc atomic layers.

Excitonic Lasing in Solution-Processed Subwavelength Nanosphere Assemblies.

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 systems 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.

Control of Light-Matter Interaction in 2D Atomic Crystals Using Microcavities

The 2D materials based on the layered structures, from graphene, to transition metal dichalcogenides (TMDs), to black phosphorous and few-layer topological insulators have emerged as novel platforms for both fundamental studies and device applications. Here, we review the progress in microcavity-enhanced light-matter interaction in 2D materials. In particular, we focus our attention on the devices based on microcavities and photonic crystals embedded with graphene and TMDs. Effects observed under the weak and strong coupling regimes are discussed followed by brief overview of future directions.

Enhancing optical nonlinearity through engineered exciton coupling in organic-inorganic nanocomposites

We show enhancement in optical nonlinear absorption by engineering the coupling between excitons of 3,4,7,8-naphthalenetetracarboxylic dianhydride (NTCDA) and ZnO nanowires. Energy transfer between the excitonic systems and exciton scattering are found to be competing processes.

Room temperature formation of microcavity polaritons in ZnO nanoparticles

We demonstrate the formation of microcavity polaritons at room temperature in a dielectric microcavity embedded with ZnO nanoparticles. Stoke shift of polariton emission is shown to be dependent on the excitonic content of the polaritons.

Formation of hybrid polaritons in an organic-inorganic microcavity at room temperature

We demonstrate hybridization of organic and inorganic excitons via strong coupling to a common microcavity mode. The system consists of 3,4,7,8-napthalenetetracarboxylic dianhydride (NTCDA) and ZnO nanocrystals embedded in a dielectric microcavity held at room temperature.