We demonstrate the growth, assembly, and characterization of ultrahigh quality polaritonic systems based on α-MoO3 microplates and nanoribbons. These micro- and nanostructures are bottom-up-synthesized single crystals with minimal impurities. By optimizing the growth conditions, we also realize morphology control of the α-MoO3 structures. We observe highly confined polariton modes in the individual structures by using scattering-type scanning near-field optical microscopy. These highly confined polariton modes are of fundamental and technological interest.
KEYWORDS: Quantum efficiency, Solid state electronics, Structural imaging, Quantum information, Transmission electron microscopy, Information technology, Quantum information processing, Diamond, Nanophotonics, Scanning electron microscopy
Ultrafast electrically driven light emitter is a critical component in the development of the high bandwidth free-space and on-chip optical communications. Traditional semiconductor based light sources for integration to photonic platform have therefore been heavily studied over the past decades. However, there are still challenges such as absence of monolithic on-chip light sources with high bandwidth density, large-scale integration, low-cost, small foot print, and complementary metal-oxide-semiconductor (CMOS) technology compatibility. Here, we demonstrate the first electrically driven ultrafast graphene light emitter that operate up to 10 GHz bandwidth and broadband range (400 ~ 1600 nm), which are possible due to the strong coupling of charge carriers in graphene and surface optical phonons in hBN allow the ultrafast energy and heat transfer. In addition, incorporation of atomically thin hexagonal boron nitride (hBN) encapsulation layers enable the stable and practical high performance even under the ambient condition. Therefore, electrically driven ultrafast graphene light emitters paves the way towards the realization of ultrahigh bandwidth density photonic integrated circuits and efficient optical communications networks.
Malte Selig, Gunnar Berghäuser, Archana Raja, Philipp Nagler, Christian Schüller, Tony Heinz, Tobias Korn, Alexey Chernikov, Ermin Malic, Andreas Knorr
Monolayers of transition metal dichalcogenides are direct gap semiconductors, which have attracted much attention in the recent past. Due to a strong Coulomb interaction, they possess strongly bound electron-hole pairs, with binding energies of hundreds of meV which is an order of magnitude larger than in conventional materials. Here, we investigate the microscopic origin of the homogeneous linewidth and coherence lifetime of excitonic resonances in monolayer molybdenum disulfide, taking exciton phonon scattering and radiative recombination into account. We find a superlinear increasing homogeneous linewidth from 2 meV at 5K to 14 meV at room temperature corresponding to a coherence lifetime of 160 fs and 25 fs.
Omer Yaffe, Yinsheng Guo, Trevor Hull, Costas Stoumpos, Liang Tan, David Egger, Fan Zheng, Guilherme Szpak, Octavi Semonin, Alexander Beecher, Tony Heinz, Leeor Kronik, Andrew Rappe, Mercouri Kanatzidis, Jonathan Owen, Marcos Pimenta, Louis Brus
We combine low frequency Raman scattering measurements with first-principles molecular dynamics (MD) to study the nature of dynamic disorder in hybrid lead-halide perovskite crystals. We conduct a comparative study between a hybrid (CH3NH3PbBr3) and an all-inorganic lead-halide perovskite (CsPbBr3). Both are of the general ABX3 perovskite formula, and have a similar band gap and structural phase sequence, orthorhombic at low temperature, changing first to tetragonal and then to cubic symmetry as temperature increases. In the high temperature phases, we find that both compounds show a pronounced Raman quasi-elastic central peak, indicating that both are dynamically disordered.
THz time-domain spectroscopy (THz TDS) with ultrafast photo-excitation is applied to probe the complex conductivity of the charge carriers in sapphire over the temperature range of 40 - 350 K. A comparison of the measured complex conductivity to the Drude model yields the carrier scattering rate and density. The dependence of the carrier scattering rate on temperature and sample purity is used to identify the scattering mechanisms in sapphire. In the higher temperature range, scattering is determined by intrinsic phonon processes, but impurity scattering becomes dominant at low temperatures in typical optical-grade samples. In high-purity samples, however, impurity scattering remains negligible down to 40 K, and carrier mobilities exceeding 10,000 cm2/Vs can be achieved.
The possibility of strong enhancement of terahertz (THz) emission from photogenerated carriers in the surface depletion region of a semiconductor under the influence of external magnetic field has been well documented in the literature. We describe a simple theory to explain the key features of this phenomenon. The model is based on a combination of the Drude-Lorentz approximation for the carrier dynamics with an appropriate solution of the radiation problem. The magnetic-field enhancement of THz emission arises primarily form the increased radiation efficiency of transient currents flowing in the plane of the surface. The model provides quantitative agreement with experiment for the pronounced angular dependence of the enhancement and predicts the correct trend for degree of enhancement in a variety of semiconductors.
The processes of desorption and dissociation for O2 on Pd(111) under femtosecond laser irradiation have been investigated. Desorption is characterize by a high yield, a nonlinear fluence dependence, and a dominant subpicosecond feature in two-pulse correlation measurements. These observations are consistent with a process driven by the high substrate electronic temperature produced by the femtosecond laser pulse. The correlation measurements also reveal the existence of a weaker feature persisting >10 ps which is attributed to an enhancement of the desorption rate by adsorbate vibrational excitation. Under the same conditions where efficient desorption is occurring, an upper limit of 5% is found for the dissociation of molecular oxygen. This is in contrast to the high branching ratio for dissociation found in thermal activation and conventional photoactivation for the same system. Explanations for the anomalous branching ratio in the femtosecond surface chemistry for O2/Pd(111) within a model involving multiple cycles of electronic excitation are examined.
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