Tunable exciton-polaritons emerging from WS2 monolayer excitons in a photonic lattice at room temperature
TL;DR: In this paper, the authors demonstrate lattice polaritons, based on an open, high-quality optical cavity, with an imprinted photonic lattice strongly coupled to excitons in a WS2 monolayer.
Abstract: Engineering non-linear hybrid light-matter states in tailored lattices is a central research strategy for the simulation of complex Hamiltonians. Excitons in atomically thin crystals are an ideal active medium for such purposes, since they couple strongly with light and bear the potential to harness giant non-linearities and interactions while presenting a simple sample-processing and room temperature operability. We demonstrate lattice polaritons, based on an open, high-quality optical cavity, with an imprinted photonic lattice strongly coupled to excitons in a WS2 monolayer. We experimentally observe the emergence of the canonical band-structure of particles in a one-dimensional lattice at room temperature, and demonstrate frequency reconfigurability over a spectral window exceeding 85 meV, as well as the systematic variation of the nearest-neighbour coupling, reflected by a tunability in the bandwidth of the p-band polaritons by 7 meV. The technology presented in this work is a critical demonstration towards reconfigurable photonic emulators operated with non-linear photonic fluids, offering a simple experimental implementation and working at ambient conditions. Excitons in atomically thin crystals couple strongly with light. Here, the authors observe lattice polaritons in a tunable open optical cavity at room temperature, with an imprinted photonic lattice strongly coupled to excitons in a WS2 monolayer.
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TL;DR: In this paper , the authors show that dipolar excitons enable controlled implementations of boson-like arrays with strong off-site interactions, in lattices with programmable geometries and more than 100 sites.
Abstract: The Hubbard model constitutes one of the most celebrated theoretical frameworks of condensed-matter physics. It describes strongly correlated phases of interacting quantum particles confined in lattice potentials1,2. For bosons, the Hubbard Hamiltonian has been deeply scrutinized for short-range on-site interactions3-6. However, accessing longer-range couplings has remained elusive experimentally7. This marks the frontier towards the extended Bose-Hubbard Hamiltonian, which enables insulating ordered phases at fractional lattice fillings8-12. Here we implement this Hamiltonian by confining semiconductor dipolar excitons in an artificial two-dimensional square lattice. Strong dipolar repulsions between nearest-neighbour lattice sites then stabilize an insulating state at half filling. This characteristic feature of the extended Bose-Hubbard model exhibits the signatures theoretically expected for a chequerboard spatial order. Our work thus highlights that dipolar excitons enable controlled implementations of boson-like arrays with strong off-site interactions, in lattices with programmable geometries and more than 100 sites.
19 citations
TL;DR: In this paper , the authors review the recent progress in the understanding of exciton optics, dynamics, and transport, which crucially govern the operation of TMD-based devices and highlight the impact of hexagonal boron nitride-encapsulation.
Abstract: Atomically thin semiconductors such as transition metal dichalcogenide (TMD) monolayers exhibit a very strong Coulomb interaction, giving rise to a rich exciton landscape. This makes these materials highly attractive for efficient and tunable optoelectronic devices. In this Research Update, we review the recent progress in the understanding of exciton optics, dynamics, and transport, which crucially govern the operation of TMD-based devices. We highlight the impact of hexagonal boron nitride-encapsulation, which reveals a plethora of many-particle states in optical spectra, and we outline the most novel breakthroughs in the field of exciton-polaritonics. Moreover, we underline the direct observation of exciton formation and thermalization in TMD monolayers and heterostructures in recent time-resolved, angle-resolved photoemission spectroscopy studies. We also show the impact of exciton density, strain, and dielectric environment on exciton diffusion and funneling. Finally, we put forward relevant research directions in the field of atomically thin semiconductors for the near future.
17 citations
TL;DR: In this article , the authors reviewed recent progress of strong coupling between exciton in transition metal dichalcogenides (TMDCs) and different resonant photonic structures, such as optical microcavities, plasmonic and all-dielectric nanocavities.
Abstract: The strong light–matter interaction between the exciton of atomically thin transition metal dichalcogenides (TMDCs) and photonic nanocavities leads to the formation of unique hybrid light-matter quasiparticles known as exciton-polaritons. The newly formed mixed state has the advantages of the photonic part such as rapid propagation and low effective mass and the highly desirable optical properties of TMDC’s exciton, including the interparticle strong interactions nonlinearity and spin-valley polarization. These joint properties make such systems an ideal platform for studying many compelling physics phenomena and open the possibility of designing novel optoelectronic devices. This work reviews recent progress of strong coupling between exciton in TMDC and different resonant photonic structures, such as optical microcavities, plasmonic and all-dielectric nanocavities. Furthermore, we discussed the unique valleytronic and nonlinear properties of TMDC monolayers in the strong coupling regime. Finally, we highlighted some of the challenges and potential future research opportunities in this field.
16 citations
TL;DR: In this paper , a topologically protected and highly interacting bound state in the continuum formed by a one-dimensional photonic crystal was used to achieve a 100 meV photonic bandgap and a Rabi splitting of 70 meV.
Abstract: Exciton–polaritons derived from the strong light–matter interaction of an optical bound state in the continuum with an excitonic resonance can inherit an ultralong radiative lifetime and significant nonlinearities, but their realization in two-dimensional semiconductors remains challenging at room temperature. Here we show strong light–matter interaction enhancement and large exciton–polariton nonlinearities at room temperature by coupling monolayer tungsten disulfide excitons to a topologically protected bound state in the continuum moulded by a one-dimensional photonic crystal, and optimizing for the electric-field strength at the monolayer position through Bloch surface wave confinement. By a structured optimization approach, the coupling with the active material is maximized here in a fully open architecture, allowing to achieve a 100 meV photonic bandgap with the bound state in the continuum in a local energy minimum and a Rabi splitting of 70 meV, which results in very high cooperativity. Our architecture paves the way to a class of polariton devices based on topologically protected and highly interacting bound states in the continuum. Combining a tungsten disulfide monolayer and a topologically protected bound state in the continuum formed by a one-dimensional photonic crystal, strong light–matter interaction enhancement and large exciton–polariton nonlinearities at room temperature are demonstrated.
6 citations
References
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TL;DR: Strong but unconventional electron-hole interactions are expected to be ubiquitous in atomically thin materials using a microscopic theory in which the nonlocal nature of the effective dielectric screening modifies the functional form of the Coulomb interaction.
Abstract: We have experimentally determined the energies of the ground and first four excited excitonic states of the fundamental optical transition in monolayer ${\mathrm{WS}}_{2}$, a model system for the growing class of atomically thin two-dimensional semiconductor crystals. From the spectra, we establish a large exciton binding energy of 0.32 eV and a pronounced deviation from the usual hydrogenic Rydberg series of energy levels of the excitonic states. We explain both of these results using a microscopic theory in which the nonlocal nature of the effective dielectric screening modifies the functional form of the Coulomb interaction. These strong but unconventional electron-hole interactions are expected to be ubiquitous in atomically thin materials.
1,910 citations
04 Apr 2014
TL;DR: In this paper, the authors developed an all-dry transfer method that relies on viscoelastic stamps and does not employ any wet chemistry step, which is found to be very advantageous to freely suspend these materials as there are no capillary forces involved in the process.
Abstract: The deterministic transfer of two-dimensional crystals constitutes a crucial step towards the fabrication of heterostructures based on the artificial stacking of two-dimensional materials. Moreover, controlling the positioning of two-dimensional crystals facilitates their integration in complex devices, which enables the exploration of novel applications and the discovery of new phenomena in these materials. To date, deterministic transfer methods rely on the use of sacrificial polymer layers and wet chemistry to some extent. Here, we develop an all-dry transfer method that relies on viscoelastic stamps and does not employ any wet chemistry step. This is found to be very advantageous to freely suspend these materials as there are no capillary forces involved in the process. Moreover, the whole fabrication process is quick, efficient, clean and it can be performed with high yield.
1,517 citations
TL;DR: In this article, the authors show that encapsulation of monolayer MoS2 in hexagonal boron nitride can efficiently suppress the inhomogeneous contribution to the exciton linewidth, as they measure in photoluminescence and reflectivity a FWHM down to 2 meV at T=4
Abstract: The strong light-matter interaction and the valley selective optical selection rules make monolayer (ML) MoS2 an exciting 2D material for fundamental physics and optoelectronics applications. But, so far, optical transition linewidths even at low temperature are typically as large as a few tens of meV and contain homogeneous and inhomogeneous contributions. This prevented in-depth studies, in contrast to the better-characterized ML materials MoSe2 and WSe2. In this work, we show that encapsulation of ML MoS2 in hexagonal boron nitride can efficiently suppress the inhomogeneous contribution to the exciton linewidth, as we measure in photoluminescence and reflectivity a FWHM down to 2 meV at T=4 K. Narrow optical transition linewidths are also observed in encapsulated WS2, WSe2, and MoSe2 MLs. This indicates that surface protection and substrate flatness are key ingredients for obtaining stable, high-quality samples. Among the new possibilities offered by the well-defined optical transitions, we measure the homogeneous broadening induced by the interaction with phonons in temperature-dependent experiments. We uncover new information on spin and valley physics and present the rotation of valley coherence in applied magnetic fields perpendicular to the ML.
540 citations
TL;DR: The results pave the way for room-temperature polaritonic devices based on multiple-quantum-well van der Waals heterostructures, where polariton condensation and electrical polariton injection through the incorporation of graphene contacts may be realized.
Abstract: Layered materials can be assembled vertically to fabricate a new class of van der Waals heterostructures a few atomic layers thick, compatible with a wide range of substrates and optoelectronic device geometries, enabling new strategies for control of light-matter coupling. Here, we incorporate molybdenum diselenide/hexagonal boron nitride (MoSe2/hBN) quantum wells in a tunable optical microcavity. Part-light-part-matter polariton eigenstates are observed as a result of the strong coupling between MoSe2 excitons and cavity photons, evidenced from a clear anticrossing between the neutral exciton and the cavity modes with a splitting of 20 meV for a single MoSe2 monolayer, enhanced to 29 meV in MoSe2/hBN/MoSe2 double-quantum wells. The splitting at resonance provides an estimate of the exciton radiative lifetime of 0.4 ps. Our results pave the way for room-temperature polaritonic devices based on multiple-quantum-well van der Waals heterostructures, where polariton condensation and electrical polariton injection through the incorporation of graphene contacts may be realized.
440 citations
TL;DR: The observation of spontaneous build-up of in-phase and antiphase ‘superfluid’ states in a solid-state system; an array of exciton–polariton condensates connected by weak periodic potential barriers within a semiconductor microcavity.
Abstract: A microcavity structure to which a periodic potential is applied has been designed, which effectively creates an array of weakly-coupled condensates. This allows the observation of fundamental dynamic behaviour, namely the build-up of certain superfluid-like states, which has been predicted for arrays of atomic Bose–Einstein condensates, but not yet observed. The effect of quantum statistics in quantum gases and liquids results in observable collective properties among many-particle systems. One prime example is Bose–Einstein condensation, whose onset in a quantum liquid leads to phenomena such as superfluidity and superconductivity. A Bose–Einstein condensate is generally defined as a macroscopic occupation of a single-particle quantum state, a phenomenon technically referred to as off-diagonal long-range order due to non-vanishing off-diagonal components of the single-particle density matrix1,2,3. The wavefunction of the condensate is an order parameter whose phase is essential in characterizing the coherence and superfluid phenomena4,5,6,7,8,9,10,11. The long-range spatial coherence leads to the existence of phase-locked multiple condensates in an array of superfluid helium12, superconducting Josephson junctions13,14,15 or atomic Bose–Einstein condensates15,16,17,18. Under certain circumstances, a quantum phase difference of π is predicted to develop among weakly coupled Josephson junctions19. Such a meta-stable π-state was discovered in a weak link of superfluid 3He, which is characterized by a ‘p-wave’ order parameter20. The possible existence of such a π-state in weakly coupled atomic Bose–Einstein condensates has also been proposed21, but remains undiscovered. Here we report the observation of spontaneous build-up of in-phase (‘zero-state’) and antiphase (‘π-state’) ‘superfluid’ states in a solid-state system; an array of exciton–polariton condensates connected by weak periodic potential barriers within a semiconductor microcavity. These in-phase and antiphase states reflect the band structure of the one-dimensional polariton array and the dynamic characteristics of metastable exciton–polariton condensates.
361 citations