Search

Nonreciprocity and nonreciprocal optical devices play a vital role in modern photonic technologies by enforcing one-way propagation of light. Here, we demonstrate an all-optical approach to nonreciprocity based on valley-selective response in transition metal dichalcogenides (TMDs). This approach overcomes the limitations of magnetic materials and it does not require an external magnetic field. We provide experimental evidence of photoinduced nonreciprocity in a monolayer WS2 pumped by circularly polarized (CP) light. Nonreciprocity stems from valley-selective exciton population, giving rise to nonlinear circular dichroism controlled by CP pump fields. Our experimental results reveal a significant effect even at room temperature, despite considerable intervalley-scattering, showing promising potential for practical applications in magnetic-free nonreciprocal platforms. As an example, here we propose a device scheme to realize an optical isolator based on a pass-through silicon nitride (SiN) ring resonator integrating the optically biased TMD monolayer., Nonreciprocity is viewed as a useful feature for many future optical devices. Here, the authors observe all-optically-induced nonreciprocal dichroism in monolayer WS2, which is explained by valley-selective response.

The development of a controllable, selective, and repeatable etch process is crucial for controlling the layer thickness and patterning of two-dimensional (2D) materials. However, the atomically thin dimensions and high structural similarity of different 2D materials make it difficult to adapt conventional thin-film etch processes. In this work, we propose a selective, damage-free atomic layer etch (ALE) that enables layer-by-layer removal of monolayer WSe2 without altering the physical, optical, and electronic properties of the underlying layers. The etch uses a top-down approach where the topmost layer is oxidized in a self-limited manner and then removed using a selective etch. Using a comprehensive set of material, optical, and electrical characterization, we show that the quality of our ALE processed layers is comparable to that of pristine layers of similar thickness. The ALE processed WSe2 layers preserve their bright photoluminescence characteristics and possess high room-temperature hole mobilities of 515 cm2/V·s, essential for fabricating high-performance 2D devices. Further, using graphene as a testbed, we demonstrate the fabrication of ultra-clean 2D devices using a sacrificial monolayer WSe2 layer to protect the channel during processing, which is etched in the final process step in a technique we call sacrificial WSe2 with ALE processing (SWAP). The graphene transistors made using the SWAP technique demonstrate high room-temperature field-effect mobilities, up to 200,000 cm2/V·s, better than previously reported unencapsulated graphene devices.

We use density functional theory (DFT) to explore the physical properties of an $Er_{ W}$ point defect in monolayer $WS_{ 2}$. Our calculations indicate that electrons localize at the dangling bonds associated with a tungsten vacancy ($V_{W}$) and at the $Er^{ 3+}$ ion site, even in the presence of a net negative charge in the supercell. The system features a set of intra-gap defect states, some of which are reminiscent of those present in isolated $Er^{ 3+}$ ions. In both instances, the level of hybridization is low, i.e., orbitals show either strong Er or W character. Through the calculation of the absorption spectrum as a function of wavelength, we identify a broad set of transitions, including one possibly consistent with the $Er^{ 3+}$ $4I_{ 15/2} \rightarrow 4I_{ 13/2}$ observed in other hosts. Combined with the low native concentration of spin-active nuclei as well as the two-dimensional nature of the host, these properties reveal $Er:WS_{ 2}$ as a potential platform for realizing spin qubits that can be subsequently integrated with other nanoscale optoelectronic devices.

The field of plasmonics, which studies the resonant interactions of electromagnetic waves and free electrons in solid-state materials1, has yet to be put to large-scale commercial application2 owing to the large amount of loss that usually occurs in plasmonic materials3. Organic light-emitting devices (OLEDs)4-7 have been incorporated into billions of commercial products because of their good colour saturation, versatile form factor8 and low power consumption9, but could still be improved in terms of efficiency and stability. Although OLEDs incorporating organic phosphors achieve an internal charge-to-light conversion of unity10, their refractive index contrast reduces the observable fraction of photons outside the device to around 25 per cent11-13. Further, during OLED operation, a localized buildup of slow-decaying14 triplet excitons and charges15 gradually reduces the brightness of the device in a process called ageing16,17, which can result in 'burn-in' effects on the display. Simultaneously improving device efficiency and stability is of paramount importance for OLED technology. Here we demonstrate an OLED that uses the decay rate enhancement18 of a plasmonic system to increase device stability, while maintaining efficiency by incorporating a nanoparticle-based out-coupling scheme to extract energy from the plasmon mode. Using an archetypal phosphorescent emitter, we achieve a two-fold increase in operational stability at the same brightness as a reference conventional device while simultaneously extracting 16 per cent of the energy from the plasmon mode as light. Our approach to increasing OLED stability avoids material-specific designs19-22 and is applicable to all commercial OLEDs that are currently used for lighting panels, televisions and mobile displays.

Integration of quantum emitters in photonic structures is an important step in the broader quest to generate and manipulate on-demand single photons via compact solid-state devices. Unfortunately, implementations relying on material platforms that also serve as the emitter host often suffer from a tradeoff between the desired emitter properties and the photonic system practicality and performance. Here, we demonstrate “pick and place” integration of a Si3N4 microdisk optical resonator with a bright emitter host in the form of ∼20-nm-thick hexagonal boron nitride (hBN). The film folds around the microdisk maximizing contact to ultimately form a hybrid hBN/Si3N4 structure. The local strain that develops in the hBN film at the resonator circumference deterministically activates a low density of defect emitters within the whispering gallery mode volume of the microdisk. These conditions allow us to demonstrate cavity-mediated out-coupling of emission from defect states in hBN through the microdisk cavity modes. Our results pave the route toward the development of chip-scale quantum photonic circuits with independent emitter/resonator optimization for active and passive functionalities.

Rotational Moulding (RM) is a versatile plastic processing method for the production of hollow products. Since the life expectancy of RM products are over several decades, prediction of mechanical properties like creep will be useful during the design phase of a product. In this research, an analytical model based on time hardening model was developed to predict and compare the creep behaviour of linear low-density polyethylene (LLDPE) and PP at 40 °C. The model uses some constants obtained from the experimental findings of a typical accelerated creep test using stepped isothermal method- time-temperature superposition (SIM-TTS). Based on the creep performance, the comparison of the two materials (LLDPE and PP) has been carried out and inferences have been made about their long term performance under constant stress.

A quasi-one-dimensional organic semiconductor, hepta(p-phenylene vinylene) (HPV), was incorporated into a DNA tensegrity triangle motif using a covalent strategy. 3D arrays were self-assembled from an HPV-DNA pseudo-rhombohedron edge by rational design and characterized by X-ray diffraction. Templated by the DNA motif, HPV molecules exist as single-molecule fluorescence emitters at the concentration of 8 mM within the crystal lattice. The anisotropic fluorescence emission from HPV-DNA crystals indicates HPV molecules are well aligned in the macroscopic 3D DNA lattices. Sophisticated nanodevices and functional materials constructed from DNA can be developed from this strategy by addressing functional components with molecular accuracy.

Description, Nanowires induce mechanical deformations in monolayer semiconductors, creating potential channels that guide optical excitations., Strain engineering is a powerful tool in designing artificial platforms for high-temperature excitonic quantum devices. Combining strong light-matter interaction with robust and mobile exciton quasiparticles, two-dimensional transition metal dichalcogenides (2D TMDCs) hold great promise in this endeavor. However, realizing complex excitonic architectures based on strain-induced electronic potentials alone has proven to be exceptionally difficult so far. Here, we demonstrate deterministic strain engineering of both single-particle electronic bandstructure and excitonic many-particle interactions. We create quasi-1D transport channels to confine excitons and simultaneously enhance their mobility through locally suppressed exciton-phonon scattering. Using ultrafast, all-optical injection and time-resolved readout, we realize highly directional exciton flow with up to 100% anisotropy both at cryogenic and room temperatures. The demonstrated fundamental modification of the exciton transport properties in a deterministically strained 2D material with effectively tunable dimensionality has broad implications for both basic solid-state science and emerging technologies.

Description, We demonstrate brightening of dark molecular isomeric states via strong coupling in optical microcavities., Polaritons in organic systems has shown the potential to modify chemical properties and to mediate long-range energy transfer between individual chromophores, among other capabilities. Here, we demonstrate that strong coupling and formation of organic exciton-polaritons can be used to selectively tune the isomer emission of organic molecules. By taking advantage of their delocalized and hybrid character, polaritons emerging in the strong coupling regime open a new relaxation pathway that allows for an efficient funneling of the excitation between the molecular isomers. We implement this by strong coupling to trans-DCS (E-4-dimethylamino-4′cyanostilbene)molecules, which present two isomers in different amounts when immersed in a polymer matrix. Thanks to this new relaxation pathway, the photoexcitation that is first shared by the common polaritonic mode is then selectively funneled to the excited states of one of the isomers, recognizing pure emission from the isomeric states that do not contribute to emission under normal conditions.

Single photon sources (quantum emitters) are a key building block for emerging quantum technologies. Especially attractive for quantum photonic circuitry is the prospect of integrating such sources with conventional photonic structures such as resonators and waveguides. In this talk, we will first present our work on realizing single photon emitters (SPEs) in hexagonal boron nitride (hBN), a van der Waals material, via strain engineering. Following this we will discuss the coupling of such SPEs to silicon nitride microdisk resonators and to plasmonic surface lattice resonances. Prospects of realizing electrically driven SPEs using few layer hBN placed in van der Waals heterostructures will also be discussed.

Transition Metal Dichalcogenides (TMDCs) have been in the limelight for the past decade as a candidate for several optoelectronic devices, and as a versatile test bed for various fundamental light-matter interaction phenomena thanks to their exceptional linear optical properties arising from their large binding energy, strong spin-orbit coupling and valley physics in the monolayer (ML) limit. They also boast strong non-linear properties fortied by excitonic responses in these systems. However, the strong second order non-linear responses are mostly restricted to the ML limit owing to crystal symmetry requirements, posing several limitations in terms of smaller interaction length and lower damage threshold. Here we demonstrate a self-hybridized exciton-polariton system in bulk WSe2 that allows us to relax the crystal symmetry rules that govern second order non-linearities. The demonstrated polariton system shows intense Second Harmonic Generation (SHG) when the fundamental wavelength is resonant with the lower polariton, with an efficiency comparable to the one from a ML WS2 when excited at the same fundamental wavelength and intensity. We model this phenomenon by considering a system with alternating second- order susceptibilities under an asymmetric electric field profile determined by the polariton mode. Helicity resolved polarization experiments show very similar non-linear response as the one from a ML where the helicity of the SHG flips with respect to the fundamental harmonic. This polaritonic system offers a platform to leverage robust second order non-linear response from centrosymmetric systems, while at the same time allowing access to third-order non-linearity inherent in strongly coupled systems.

We report enhanced second harmonic generation (SHG) from centrosymmetric bulk WSe2. This enhancement arises due to pumping in resonance with the Exciton-Polariton modes formed in self-hybridized bulk WSe2.

We demonstrate significant enhancement (> 40%) in valley coherence of localized excitons in monolayer WS2 via strain engineering. The observed enhancement is attributed to the suppression of inter valley scattering due to strain induced potential.

We demonstrate room-temperature ultralong-range transport >80 pm of exciton- polaritons in a disordered organic thin-film using a one-sided distributed Bragg reflector, which is orders of magnitude larger than expected for excitons in disordered systems.

There is growing interest in using strongly coupled organic microcavities to tune molecular dynamics, including the electronic and vibrational properties of molecules. However, very little attention has been paid to the utility of cavity polaritons as sensors for out-of-equilibrium phenomena, including thermal excitations. Here, we demonstrate that non-resonant infrared excitation of an organic microcavity system induces a transient response in the visible spectral range near the cavity polariton resonances. We show how these optical responses can be understood in terms of ultrafast heating of electrons in the metal cavity mirror, which modifies the effective refractive index and subsequently the strong coupling conditions. The temporal dynamics of the microcavity are strictly determined by carriers in the metal, including the cooling of electrons via electron–phonon coupling and excitation of propagating coherent acoustic modes in the lattice. We rule out multiphoton excitation processes and verify that no real polariton population exists despite their strong transient features. These results suggest the cavity polaritons to be promising as sensitive probes of non-equilibrium phenomena.

Color centers in wide bandgap semiconductors are attracting broad attention as platforms for quantum technologies relying on room-temperature single-photon emission (SPE), and for nanoscale metrology applications building on the centers' response to electric and magnetic fields. Here, we demonstrate room-temperature SPE from defects in cubic boron nitride (cBN) nanocrystals, which we unambiguously assign to the cubic phase using spectrally resolved Raman imaging. These isolated spots show photoluminescence (PL) spectra with zero-phonon lines (ZPLs) within the visible region (496-700 nm) when subject to sub-bandgap laser excitation. Second-order autocorrelation of the emitted photons reveals antibunching with $g^{2}$ ~ 0.2 and a decay constant of 2.75 ns that is further confirmed through fluorescence lifetime measurements. The results presented herein prove the existence of optically addressable isolated quantum emitters originating from defects in cBN, making this material an interesting platform for opto-electronic devices and quantum applications., 7 pages, 3 figures

Strong light-matter coupling results in the formation of half-light half-matter quasiparticles that take on the desirable properties of both systems such as small mass and large interactions. Controlling this coupling strength in real-time is highly desirable due to the large change in optical properties such as reflectivity that can be induced in strongly coupled systems. Here we demonstrate modulation of strong exciton-photon coupling in a monolayer WS2 through electric field induced gating at room temperature. The device consists of a WS2 field effect transistor embedded inside a microcavity structure which transitions from strong to weak coupling when the monolayer WS2 becomes more n-type under gating. This transition occurs due to the reduction in oscillator strength of the excitons arising from decreased Coulomb interaction in the presence of electrostatically induced free carriers. The possibility to electrically modulate a solid state system at room temperature from strong to weak coupling is highly desirable for realizing low energy optoelectronic switches and modulators operating both in quantum and classical regimes.

Atomically thin transition metal dichalcogenides (TMDs) possess a number of properties that make them attractive for realizing room-temperature polariton devices. An ideal platform for manipulating polariton fluids within monolayer TMDs is that of Bloch surface waves, which confine the electric field to a small volume near the surface of a dielectric mirror. Here we demonstrate that monolayer tungsten disulfide ($\text{WS}_2$) can sustain Bloch surface wave polaritons (BSWPs) with a Rabi splitting of 43 meV and propagation constants reaching 33 $\mu$m. In addition, we evidence strong polariton-polariton nonlinearities within BSWPs, which manifest themselves as a reversible blueshift of the lower polariton resonance by up to 12.9$\pm$0.5 meV. Such nonlinearities are at the heart of polariton devices and have not yet been demonstrated in TMD polaritons. As a proof of concept, we use the nonlinearity to implement a nonlinear polariton source. Our results demonstrate that BSWPs using TMDs can support long-range propagation combined with strong nonlinearities, enabling potential applications in integrated optical processing and polaritonic circuits., Comment: 7 pages, 4 figures

The control and enhancement of resonance energy transfer is highly desirable for a variety of applications ranging from solar cells to spectroscopic rulers. However, the process of direct resonance energy transfer is distance dependent and limited to ∼10 nm for typical donor–acceptor pairs. Here we demonstrate long-range (∼160 nm) direct energy transfer between donor quantum dots and acceptor dye molecules through the use of an optical topological transition (OTT) in a metamaterial. The OTT in a metamaterial, modifies the density of states between the donor and acceptor, resulting in the long-range energy transfer with transfer efficiency of ∼32%. Theoretical calculation based on master-equation formalism is used to model the system and is found to be in good agreement with the experimental observation. The use of OTTs in metamaterials to enhance and control energy transfer process can have wide array of potential applications ranging from organic solar cells to quantum entanglement.

The treatment of critical sized bone defect remains a significant challenge in orthopedics. The objective of the study is to evaluate the effect of the combination of bone morphogenetic protein 2 (BMP2) expressing genetically engineered mesenchymal stem cells (MSCs) [MSCs engineered using a multimam vector, pAceMam1, an emerging gene delivery vector] and an osteoconductive scaffold [silica coated nanohydroxyapatite-gelatin reinforced with fibers] in enhancing bone regeneration in critical sized segmental defects. The scaffold with transfected MSCs showed significantly higher viability, proliferation and osteogenic differentiation in vitro. Further, this group augmented union and new bone formation in critical sized rat femoral segmental defect at 12 weeks when compared to control groups (scaffold with MSCs and scaffold alone). These data demonstrated that the MSCs engineered for transient expression of BMP2 can improve the repair of segmental defects, which paves an avenue for using pAceMam1 as a vector for bone tissue regeneration.

Efficient Forster resonant energy transfer is observed between excitons in a two-dimensional (2D) monolayer of the transition metal dichalcogenide, MoSe2, and an 2 nm thick layer of the organic material, 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA). The exciton transition dipoles are horizontally aligned, enabling efficient energy transfer between these dissimilar materials. Energy transfer is observed using time-resolved and steady state photoluminescence and photoluminescence excitation spectroscopy. Time-resolved measurements show a reduction in the donor (PTCDA) lifetime, and steady state emission experiments show a decrease in donor and an increase in acceptor (MoSe2) emission. Photoluminescence excitation spectra show a spectral dependence of the energy transfer process, with a maximum efficiency at the absorption maximum of the donor. The planar dipole orientation is determined using Fourier space imaging. The efficient energy transfer from low mobility organic materials to higher mobility...

We study the optoelectronic properties of a type-II heterojunction (HJ) comprising a monolayer of the transition metal dichalcogenide (TMDC), WS2, and a thin film of the organic semiconductor, 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA). Both theoretical and experimental investigations of the HJ indicate that Frenkel states in the organic layer and two-dimensional Wannier–Mott states in the TMDC dissociate to form hybrid charge transfer excitons at the interface that subsequently dissociate into free charges that are collected at opposing electrodes. A photodiode employing the HJ achieves a peak external quantum efficiency of 1.8 ± 0.2% at a wavelength of 430 ± 10 nm, corresponding to an internal quantum efficiency (IQE) as high as 11 ± 1% in these ultrathin devices. The photoluminescence spectra of PTCDA and PTCDA/WS2 thin films show that excitons in the WS2 have a quenching rate that is approximately seven times higher than in PTCDA. This difference leads to strong wavelength dependence in IQE.

We report on the room-temperature single photon emission dynamics originating from defect states in hBN. Photo induced modification of the emission characteristics of thee defects under blue and green illumination is shown.

Two-dimensional van der Waals (vdW) materials have emerged as a very attractive class of optoelectronic material due to the unprecedented strength in its interaction with light. Approaches to enhance this interaction even further using photonic structures such as microcavities and metamaterials is highly attractive for both fundamental investigations as well as for applications such as light emitting diodes and quantum technologies.

Optical waveguides are vital components of data communication system technologies, but their scaling down to the nanoscale has remained challenging despite advances in nano-optics and nanomaterials. Recently, we theoretically predicted that the ultimate limit of visible photon guiding can be achieved in monolayer-thick transition metal dichalcogenides. Here, we present an experimental demonstration of light guiding in an atomically thick tungsten disulfide membrane patterned as a photonic crystal structure. In this scheme, two-dimensional tungsten disulfide excitonic photoluminescence couples into quasi-guided photonic crystal modes known as resonant-type Wood’s anomalies. These modes propagate via total internal reflection with only a small portion of the light diffracted to the far field. Such light guiding at the ultimate limit provides more possibilities to miniaturize optoelectronic devices and to test fundamental physical concepts. A monolayer WS2 membrane patterned as a photonic crystal sustains guided optical modes that propagate via total internal reflection.

We demonstrate coupling of hBN defect emission to Si3N4 microdisk cavities and high-Q plasmonic surface lattice resonances by exploiting the topography of the photonic elements to engineer strain-activated color centers within the element’s field-mode.

Half-light half-matter quasiparticles termed exciton-polaritons arise through the strong coupling of excitons and cavity photons. They have been used to demonstrate a wide array of fundamental phenomena and potential applications ranging from Bose-Einstein like condensation to analog Hamiltonian simulators and chip-scale interferometers. Recently the two dimensional transition metal dichalcogenides (TMDs) owing to their large exciton binding energies, oscillator strength and valley degree of freedom have emerged as a very attractive platform to realize exciton-polaritons at elevated temperatures. Achieving electrical injection of polaritons is attractive both as a precursor to realizing electrically driven polariton lasers as well as for high speed light-emitting diodes (LED) for communication systems. Here we demonstrate an electrically driven polariton LED operating at room temperature using monolayer tungsten disulphide (WS2) as the emissive material. To realize this device, the monolayer WS2 is sandwiched between thin hexagonal boron nitride (hBN) tunnel barriers with graphene layers acting as the electrodes. The entire tunnel LED structure is embedded inside a one-dimensional distributed Bragg reflector (DBR) based microcavity structure. The extracted external quantum efficiency is ~0.1% and is comparable to recent demonstrations of bulk organic and carbon nanotube based polariton electroluminescence (EL) devices. The possibility to realize electrically driven polariton LEDs in atomically thin semiconductors at room temperature presents a promising step towards achieving an inversionless electrically driven laser in these systems as well as for ultrafast microcavity LEDs using van der Waals materials.

Cooperative phenomena stemming from radiation-field-mediated coupling between individual quantum emitters are presently attracting broad interest for on-chip photonic quantum memories and long-range entanglement. Common to these applications is the generation of electromagnetic modes over macroscopic distances. Much research, however, is still needed before such systems can be deployed in the form of practical devices, starting with the investigation of alternate physical platforms. Quantum emitters in two-dimensional (2D) systems provide an intriguing route because these materials can be adapted to arbitrarily shaped substrates to form hybrid systems where emitters are near-field-coupled to suitable optical modes. Here, we report a scalable coupling method allowing color center ensembles in a van der Waals material - hexagonal boron nitride - to couple to a delocalized high quality plasmonic surface lattice resonance. This type of architecture is promising for photonic applications, especially given the ability of the hexagonal boron nitride emitters to operate as single-photon sources at room temperature., Comment: 8 pages, 4 Figures

Sub-wavelength nanostructured systems with tunable electromagnetic properties, such as hyperbolic metamaterials (HMMs), provide a useful platform to tailor spontaneous emission processes. Here, we investigate a system comprising $Eu^{ 3+}(NO_{3})_{3}6H_{2}O$ nanocrystals on an HMM structure featuring a hexagonal array of Ag-nanowires in a porous $Al_{2}O_{3}$ matrix. The HMM-coupled $Eu^{ 3+}$ ions exhibit up to a 2.4-fold increase of their decay rate, accompanied by an enhancement of the emission rate of the $^{ 5}D_{0}\rightarrow$ $^{ 7}F_{2}$ transition. Using finite-difference time-domain modeling, we corroborate these observations with the increase in the photonic density of states seen by the $Eu^{ 3+}$ ions in the proximity of the HMM. Our results indicate HMMs can serve as a valuable tool to control the emission from weak transitions, and hence hint at a route towards more practical applications of rare-earth ions in nanoscale optoelectronics and quantum devices.

The low quantum yield observed in two-dimensional semiconductors of transition metal dichalcogenides (TMDs) has motivated the quest for approaches that can enhance the light emission from these systems. Here, we demonstrate broadband enhancement of spontaneous emission and increase in Raman signature from archetype two-dimensional semiconductors: molybdenum disulfide (MoS2) and tungsten disulfide (WS2) by placing the monolayers in the near field of a photonic hypercrystal having hyperbolic dispersion. Hypercrystals are characterized by a large broadband photonic density of states due to hyperbolic dispersion while having enhanced light in/out coupling by a subwavelength photonic crystal lattice. This dual advantage is exploited here to enhance the light emission from the 2D TMDs and can be utilized for developing light emitters and solar cells using two-dimensional semiconductors.

Surface-enhanced Raman scattering (SERS) is commonly associated with noble metal substrates. However, over the years modest Raman enhancements ( 3 × 105 enhancement in SERS signal from an organic molecule (4-mercaptopyridine) placed in the near field of a two-dimensional semiconductor molybdenum disulfide (MoS2) monolayer. This large enhancement in the SERS signal is attributed to the charge transfer (CT) state formed at the interface of the 2D semiconductor and organic molecule and is found to occur when the excitation source is chosen to be in resonance with the CT state. This approach provides a new strategy for carrying out SERS experiments on molecules with very weak Raman sig...

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.

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.

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.

Amorphous molecular solids are inherently disordered, exhibiting strong exciton localization. Optical microcavities containing such disordered excitonic materials have been theoretically shown to support both propagating and localized exciton-polariton modes. Here, the ultrastrong coupling of a Bloch surface wave photon and molecular excitons in a disordered organic thin film at room temperature is demonstrated, where the major fraction of the polaritons are propagating states. The delocalized exciton-polariton has a group velocity as high as 3 × 107 m s-1 and a lifetime of 500 fs, leading to propagation distances of over 100 µm from the excitation source. The polariton intensity shows a halo-like pattern that is due to self-interference of the polariton mode, from which a coherence length of 20 µm is derived and is correlated with phase breaking by polariton scattering. The demonstration of ultralong-range exciton-polariton transport at room temperature promises new photonic and optoelectronic applications such as efficient energy transfer in disordered condensed matter systems.

We present an approach to dynamically control the interaction between excitons in monolayer WS 2 and microcavity photons at room temperature. This is achieved by tuning the oscillator strength of the WS 2 excitons in the presence of charged carriers induced by electrostatic gating.

We have observed directional spontaneous emission of rhodamine 6G dye deposited on top of a silver grating and found that its angular distribution patterns were very different in TE and TM polarizations. The latter was related to the dispersion curves determined based on the polarized reflection spectra measured at multiple incidence angles. The most intriguing finding of this Letter was a resonance, which was coupled with TE-polarized light and determined the characteristic double-crescent patterns in the TE-polarized spontaneous emission. This observation, as well as nearly similar resonance observed in TM polarization, was tentatively explained in terms of leaky waveguide modes supported by a film of dye-doped polymer.

We demonstrate the tuning of the exciton-polaritons in monolayer WS 2 embedded in a microcavity via electrostatic gating at room temperature. Under high electron doping the formation of polaritons with the charged excitons is observed.

We demonstrate redistribution of the spectral intensities of the luminescence associated with different vibronic transitions in organic molecule, Diindenoperylene through strong coupling of excitons to surface plasmons.

Room temperature quantum emitter arrays are created in hexagonal Boron Nitride (hBN) by deterministic activation via strain engineering on a nanopillar substrate. Emitters are localized at pillar edges where the hBN film undergoes maximum strain.

We have observed double crescent patterns in the TE polarized spontaneous emission of rhodamine 6G dye deposited onto silver grating metasurface. It originates from the surface wave characterized by the effective index of refraction n=1.03.

Two dimensional (2D) atomic crystals of graphene, and transition metal dichalcogenides have emerged as a class of materials that show strong light-matter interaction. This interaction can be further controlled by embedding such materials into optical microcavities. When the interaction is engineered to be stronger than the dissipation of light and matter entities, one approaches the strong coupling regime resulting in the formation of half-light half-matter bosonic quasiparticles called microcavity polaritons. Here we report the evidence of strong light-matter coupling and formation of microcavity polaritons in a two dimensional atomic crystal of molybdenum disulphide (MoS2) embedded inside a dielectric microcavity at room temperature. A Rabi splitting of 46 meV and highly directional emission is observed from the MoS2 microcavity owing to the coupling between the 2D excitons and the cavity photons. Realizing strong coupling effects at room temperature in a disorder free potential landscape is central to the development of practical polaritonic circuits and switches., 25 pages, 7 figures

Significance Light–matter interaction lies at the heart of several fundamental phenomena and technological applications ranging from photosynthesis to lasers. Current approaches to control this interaction such as optical cavities, photonic crystals, and metamaterials either rely on frequency resonance mechanisms which limit the bandwidth or suffer from poor light-coupling issues. Here we report a class of artificial media: photonic hypercrystals to control light–matter interactions. Both bandwidth and outcoupling limitations are overcome using hypercrystals. This characteristic is demonstrated through simultaneous enhancement of spontaneous emission rate (20×) and outcoupling (100×) from quantum dots embedded in the hypercrystal. This platform for broadband control of light–matter interaction will push the boundaries of applications such as ultrafast light-emitting diodes, photovoltaics, and quantum informatics.

Energy transfer from low mobility material to high mobility material is essential for optoelectronic application. We demonstrate Foster energy transfer from organic material (PTCDA) to monolayer MoSe 2 though steady state and transient photoluminescence spectroscopy.

We demonstrate deterministic formation of quantum emitter arrays in hexagonal Boron Nitride (hBN) at room temperature. The emitters are localized around the location of high strain provided by the nanopillar substrate.

We demonstrate broadband enhancement of light emission from quantum dots, single photon emitters and 2D semiconductors using photonic hypercrystals (PHC). Both out-coupling and spontaneous emission rate are increased from the different emitters.

Recent advances in condensed matter physics have shown that the valley degree of freedom of electrons in 2D materials with hexagonal symmetry, such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDs), can be efficiently exploited, leading to the emergent field of valleytronics, which offers unique opportunities for efficient data transfer, computing and storage. The ability to couple the valley degree of freedom of electrons with light can further expand the ways one manipulates this degree of freedom, thus envisioning a new class of solid-state-photonic interfaces and devices. Besides this expansion of control of valley by light-waves, coupling of photons with valley-polarized electrons can dramatically expand the landscape of available optical responses, which may bring new means of controlling light in photonic devices. In this work we design such hybrid solid-state photonic metasurface integrating 2D TMD and photonic all-dielectric metasurface. While TMD is naturally endowed with the property of valley to optical-polarization coupling, the photonic metasurface is designed to produce chiral field which selectively couples to the valley degree of freedom of solid-state TMD component. We experimentally demonstrate that such coupling leads to controlled valley polarization due to the coupling of 2D materials with the chiral photonic metasurface. The measured emission from valley excitons in this hybrid system yields the preferential emission of specific helicity.

We investigate the propagation of surface plasmon polaritons (SPPs) in thin films of topological insulators. Cases of single films and multilayered stacks are analyzed. The materials considered are second generation three dimensional topological insulators Bi2Se3, Bi2Te3, and Sb2Te3. Dispersion relations and propagation lengths of SPPs are estimated numerically, taking into account the variation of bulk dielectric functions of topological insulators, as well as substrate, using the Drude-Lorentz model. The key factors affecting propagation length are identified and experimental modifications for tuning the dispersion relations are proposed. The apparent discrepancy between the experimental data and previously considered theory is resolved.