31 research outputs found
Optical nonlinearity goes ultrafast in 2D semiconductor-based nanocavities
: Hybrid systems of silver nanodisks strongly coupled to monolayer tungsten-disulfide (WS2) show giant room-temperature nonlinearity due to their deeply sub-wavelength localized nature, resulting in ultrafast modifications of nonlinear absorption in a solid-state system
Ultrafast flow of interacting organic polaritons
The strong-coupling of an excitonic transition with an electromagnetic mode
results in composite quasi-particles called exciton-polaritons, which have been
shown to combine the best properties of their bare components in semiconductor
microcavities. However, the physics and applications of polariton flows in
organic materials and at room temperature are still unexplored because of the
poor photon confinement in such structures. Here we demonstrate that polaritons
formed by the hybridization of organic excitons with a Bloch Surface Wave are
able to propagate for hundreds of microns showing remarkable third-order
nonlinear interactions upon high injection density. These findings pave the way
for the studies of organic nonlinear light-matter fluxes and for a
technological promising route of dissipation-less on-chip polariton devices
working at room temperature.Comment: Improved version with polariton-polariton interactions. 13 pages, 4
figures, supporting 6 pages, 6 figure
The enhancement of excitonic emission crossing Saha equilibrium in trap passivated CH3NH3PbBr3 perovskite
Metal-halide semiconductor perovskites have received great attention for the development of stable and efficient light emitting diodes and lasers, since they combine high charge carrier mobility and light emission spectral-purity with low-cost fabrication methods. Nevertheless, the role of excitons, free carries and trap states in perovskite light emission properties is still unclear due to their interdependence. In this paper we selectively manage trapping and light emission mechanisms by a reversible laser-assisted trap-passivation process performed on a CH3NH3PbBr3 perovskite layer, coupled to the inner modes of a high-quality micro-cavity, which only affects the radiative recombination. We show that photoluminescence is dominated by exciton radiative decay process and that trap states passivation increases the exciton gemination rate by reducing coulombic scattering of free electrons due to the ionized impurities. This picture provides a more general description than the model based on trap states-free Saha thermodynamic equilibrium between photo-generated species. The interdependence of free carries, trap states and excitons in the light emission properties of CH3NH3PbBr3 perovskite thin films and their relationship to device performance is a subject of debate. Here, the authors investigate the role of non-radiative recombination and demonstrate that the photoluminescence is dominated by exciton radiative decay processes
Hyperspectral microscopy of two-dimensional semiconductors
Here we present an interferometric wide field hyperspectral microscope based on a common-path birefringent interferometer with translating wedges, to measure photoluminescence emission from two-dimensional semiconductors. We show diffraction-limited hyperspectral photoluminescence microscopy from two-dimensional materials across millimeter areas, proving that our hyperspectral microscope is a compact, stable and fast tool to characterize the optical properties and the morphology of 2D materials across ultralarge areas
Strong Coupling of Coherent Phonons to Excitons in Semiconducting Monolayer MoTe
The coupling of the electron system to lattice vibrations and their
time-dependent control and detection provides unique insight into the
non-equilibrium physics of semiconductors. Here, we investigate the ultrafast
transient response of semiconducting monolayer 2-MoTe encapsulated with
BN using broadband optical pump-probe microscopy. The sub-40-fs pump pulse
triggers extremely intense and long-lived coherent oscillations in the spectral
region of the A' and B' exciton resonances, up to 20% of the maximum
transient signal, due to the displacive excitation of the out-of-plane
phonon. Ab-initio calculations reveal a dramatic rearrangement of the optical
absorption of monolayer MoTe induced by an out-of-plane stretching and
compression of the crystal lattice, consistent with an -type
oscillation. Our results highlight the extreme sensitivity of the optical
properties of monolayer TMDs to small structural modifications and their
manipulation with light.Comment: 27 pages, 4 figures, supporting informatio