Polariton Interactions Research Articles

Room temperature ballistic transport of exciton-polaritons in a one-dimensional whispering gallery microcavity

In this work, we report the experimental observation of the ballistic transport of condensed exciton-polaritons at room temperature in a one-dimensional whispering-gallery microcavity. Such coherent transport, initiated by the pronounced inter-particle interactions of polaritons, leads to the generation of two symmetric emission beams in the momentum (angular) space. By means of spatially filtered angle-resolved photoluminescence imaging spectroscopy, we were able to identify their origin and successfully rationalize these observations using the potential energy-to-kinetic energy conversion picture. The energy-dependent emission linewidth, as well as TM to TE inter-mode scattering, have also been discussed.

Origin of Exciton-Polariton Interactions and Decoupled Dark States Dynamics in 2D Hybrid Perovskite Quantum Wells.

The realization of efficient optical devices depends on the ability to harness strong nonlinearities, which are challenging to achieve with standard photonic systems. Exciton-polaritons formed in hybrid organic-inorganic perovskites offer a promising alternative, exhibiting strong interactions at room temperature (RT). Despite recent demonstrations showcasing a robust nonlinear response, further progress is hindered by an incomplete understanding of the microscopic mechanisms governing polariton interactions in perovskite-based strongly coupled systems. Here, we investigate the nonlinear properties of quasi-2D dodecylammonium lead iodide perovskite (n3-C12) crystals embedded in a planar microcavity. Polarization-resolved pump-probe measurements reveal the contribution of indirect exchange interactions assisted by dark states formation. Additionally, we identify a strong dependence of the unique spin-dependent interaction of polaritons on sample detuning. The results are pivotal for the advancement of polaritonics, and the tunability of the robust spin-dependent anisotropic interaction in n3-C12 perovskites makes this material a powerful choice for the realization of polaritonic circuits.

Stability of vortices in exciton-polariton condensates with spin–orbital-angular-momentum coupling

The existence and dynamics of stable quantized vortices is an important subject of quantum many-body physics. Spin–orbital-angular-momentum coupling (SOAMC), a special type of spin–orbit coupling, has been experimentally achieved to create vortices in atomic Bose–Einstein condensates (BEC). Here, we generalize the concept of SOAMC to a two-component polariton BEC and analyze the emergence and configuration of vortices under a finite-size circular pumping beam. We find that the regular configuration of vortex lattices induced by a finite-size circular pump is significantly distorted by the spatially dependent Raman coupling of SOAMC, even in the presence of a repulsive polariton interaction which can assist the forming of stable vortex configuration. Meanwhile, a pair of vortices induced by SOAMC located at the center of polariton cloud remains stable. When the Raman coupling is sufficiently strong and interaction is weak, the vortices spiraling in from the edge of polariton cloud will disrupt the polariton BEC.

Magnetic field-induced phase transition in spinor exciton-polaritons condensate

We theoretically study the magnetic phase transition of condensed exciton-polariton microcavities in an applied magnetic field. When the magnetic field is strong, all polariton spins are polarized parallel to the magnetic field as usual. On the contrary, in the weak magnetic-field region, the polariton polarization degree is negative, namely, anti-parallel to the magnetic field. For a strong magnetic field, the magnetic phase of the polaritons arises and leads to a paramagnetic, while around a weak magnetic field, with zero exciton–photon detunings, and weak Rabi splitting the spin polarization of the polaritons leads to a diamagnetic. Thus, magneto-polariton phase transition polarization originates from the competition between the polariton Zeeman effect and polariton–polariton interactions. Moreover, the polariton polarization strongly depends on the exciton–photon detuning and Rabi splitting and has a large negative value as they are both small. At last, we compare our theoretical results with the experiments and find they match each other very well.

Polarized-SERS of non-isotropic molecules on thermally-induced corrugated plasmonic surface supporting a NIR-SPP mode

Thermally-induced surface reconstruction of α-Al2O3 was used to fabricate corrugated templates of different periods to support percolated ultrathin metal film. Reflectance analysis and simulations revealed the coupling of a hybrid NIR-SPP mode along its corrugation vector (kcorrugation). The fabricated samples enhanced Raman signals of phenyl thiolates (PT) with reduced photo-induced disadvantages at λexc = 785 nm. Polarized SERS were performed to study adsorbed molecule – polariton interaction on these corrugated thin film surface. A twofold SERS anisotropy with a cos2(σ) dependency (σ = azimuthal angle) was observed. SERS dichroism of PT Raman modes of different polarizability tensors were analysed. A more pronounced dependence on corrugation period was observed for totally symmetric a1 modes than the non-totally symmetric b1 and b2 modes. Apart from the relative SERS intensity, their SERS dichroism was determined mostly by the excitation of SPP along the kcorrugation rather than the orientation of PT on sample surface. Edge-on orientation of adsorbed PT was predicted due to the absence of a2 modes with both tensor components parallel to the surface. Shorter corrugation periods fabricated were reproducible and ample for uniform, large-area sensing due to effective SPP coupling at σ = 0° resulting in a spatially extended SERS excitation volume.

Recombination dynamics and pronounced re-absorption effect in ZnO single crystals under two-photon excitation

Time-resolved photoluminescence measurements were conducted on ZnO single crystals using two-photon (2P) excitation at low temperatures ranging from 25 to 260 K. The decay constants of various emission peaks are determined and compared between one-photon and two-photon excitations using a recently modified localized-state ensemble model. The analysis is focused on the redshift of the phonon-assisted free exciton transition energy with increasing temperature. A significantly longer radiative recombination lifetime of approximately 840 ps is observed under 2P excitation. The extended lifetime of excitons during 2P excitation is achieved through the interplay of multiple mechanisms. Photon-recycling, enabled by high absorption coefficients and total internal reflection, facilitates re-absorption and new carrier generation. Phonon scattering lowers photon energy, allowing their escape from the crystal, while exciton–polariton interactions delay photon travel, collectively contributing to the extension of exciton lifetimes. The re-absorption effect and elongated carrier lifetime observed from our work could be beneficial for applications of ZnO materials in 2P imaging, particularly of biological samples.

In English

We investigated influence of multiwalled carbon nanotubes (CNTs) on spectral characteristics of composites “thermo-expanded graphite – carbon nanotubes (TEG–CNTs)”. The introduction of CNTs in an amount of 0-3% by weight of TEG composites results in a significant increase in the strength characteristics and thermal stability of the composites. This result indicates that CNTs is ideal filler for composites based on TEG compositions and structures. Measurements the giant two-polar oscillations with very small half-width 0.5 cm–1 testify the strong interaction of surface polaritons with photons. When frequencies of local oscillations of surface bonds of carbon nanotubes and modes along “nanotube-TEG” boundaries matches, then the light absorption increases 102–105 times. Thus, IR absorption with two-polar oscillations was measured at 0% of nanotubes in TEG at frequency of 2750 cm–1. It is own optical mode in the thermally expanded graphite. 5 peaks with two-polar oscillations were measured in the IR absorption spectra at 1% of carbon nanotubes. And 8 peaks with two-polar oscillations were measured at 3 % of carbon nanotubes at optical mode frequencies along the boundaries of thermally expanded graphite - carbon nanotubes. When frequencies of local oscillations of carbon nanotubes and composite’s modes matches, then the light absorption extremely increases (in 102–105 times), and two-polar IR absorption oscillations with negative components are formed. In general, two-photon interference is a result of quantum entanglement of dipole-active oscillations and splitting of photons according to the Hong-Ou-Mendel (HOM) quantum effect. Two-photon entanglement is built on the basis of the most entanglement states, also known as Bell's states. The HOM–quantum effect on composites “expanded graphite-carbon nanotubes” is promising for the development of highly coherent optical quantum computers.

Excitation and modulation of long-range surface plasmons based on InSb multilayer structure

We proposed an Ag-based multilayer InSb and SiO2 system in the terahertz region. Based on the surface plasmon polariton (SPP) interaction among each interface, the spontaneous emission of a dipole in multilayer systems supporting SPP and waveguide modes is theoretically studied. It found that the coupling efficiency of long-range SPP (LRSPP) is about 78% with a propagation length of up to 28.25 mm. The thermally tunable characteristics of InSb enable LRSPP devices to be realized with adjustable coupling efficiency. Our work could be applied as a future guide for integrated plasmonic device design.

Ultrafast imaging of polariton propagation and interactions

Semiconductor excitations can hybridize with cavity photons to form exciton-polaritons (EPs) with remarkable properties, including light-like energy flow combined with matter-like interactions. To fully harness these properties, EPs must retain ballistic, coherent transport despite matter-mediated interactions with lattice phonons. Here we develop a nonlinear momentum-resolved optical approach that directly images EPs in real space on femtosecond scales in a range of polaritonic architectures. We focus our analysis on EP propagation in layered halide perovskite microcavities. We reveal that EP–phonon interactions lead to a large renormalization of EP velocities at high excitonic fractions at room temperature. Despite these strong EP–phonon interactions, ballistic transport is maintained for up to half-exciton EPs, in agreement with quantum simulations of dynamic disorder shielding through light-matter hybridization. Above 50% excitonic character, rapid decoherence leads to diffusive transport. Our work provides a general framework to precisely balance EP coherence, velocity, and nonlinear interactions.

Controllability of shock waves in one-dimensional polariton condensates

In one-dimensional incoherent pumped exciton–polariton condensates, we realize the generation and control of supersonic shock waves. By choosing a suitable initial input wave, we obtain the region of existence of various shock waves as a function of the phase of the initial wave, the coefficient of polariton interaction, the coefficient of the interaction between polariton and reservoir and the condensation rate and intensity of pumping. Using these results, we discuss the effect of different parameters on shock waves composed of two shock waves, and find that the gain and loss will result in a sloping platform between two waves. In addition, we also consider the effect of the non-adiabatic approximation and the diffusion coefficient of the reservoir on the profiles of the shock waves. We find that the non-adiabatic approximation will result in some small oscillations on the uniform background, and the platform between two waves becomes flat; however, the diffusion effect of the reservoir will clear these small oscillations and tilt the platform. Our results may pave the way to control shock waves in an incoherent pumped exciton–polariton system.

Near-field spectroscopy of Dirac plasmons in Bi2Se3 ribbon arrays

Plasmons supported in the massless electron surface states of topological insulators (TIs), known as Dirac plasmons, have great potential in next generation optoelectronics. However, their inherent confinement to the surface makes the investigation of Dirac plasmons challenging. Near-field techniques provide the ideal platform to directly probe Dirac plasmons due to the sensitivity to evanescent fields at the surface. Here, we demonstrate the use of aperture near-field spectroscopy for the investigation of localized terahertz (THz) Dirac plasmon resonances in Bi2Se3 ribbon arrays with widths ranging from 10 to 40 µm. Unlike scattering THz near-field techniques, the aperture method is most sensitive to plasmons with the relevant lower-momenta corresponding to plasmon wavelengths on the scale of ∼20 µm. The combination of THz time-domain spectroscopy and aperture near-field microscopy enables sampling of localized Dirac plasmons in the near-field zone in the 0.5–2.5 THz range. We map the plasmon dispersion, which reveals a coupled plasmon–phonon polariton interaction. The near-field spectra show a higher contrast of the upper polariton branch in comparison with far-field observations. The information revealed by aperture near-field spectroscopy could deepen our understanding of the behavior of Dirac plasmons, leading to the potential development of real-world TI devices.

Uncovering temperature-dependent exciton-polariton relaxation mechanisms in hybrid organic-inorganic perovskites

Hybrid perovskites have emerged as a promising material candidate for exciton-polariton (polariton) optoelectronics. Thermodynamically, low-threshold Bose-Einstein condensation requires efficient scattering to the polariton energy dispersion minimum, and many applications demand precise control of polariton interactions. Thus far, the primary mechanisms by which polaritons relax in perovskites remains unclear. In this work, we perform temperature-dependent measurements of polaritons in low-dimensional perovskite wedged microcavities achieving a Rabi splitting of {{{hslash }}Omega }_{{Rabi}} = 260 ± 5 meV. We change the Hopfield coefficients by moving the optical excitation along the cavity wedge and thus tune the strength of the primary polariton relaxation mechanisms in this material. We observe the polariton bottleneck regime and show that it can be overcome by harnessing the interplay between the different excitonic species whose corresponding dynamics are modified by strong coupling. This work provides an understanding of polariton relaxation in perovskites benefiting from efficient, material-specific relaxation pathways and intracavity pumping schemes from thermally brightened excitonic species.

Exciton polariton interactions in Van der Waals superlattices at room temperature

Monolayer transition-metal dichalcogenide (TMD) materials have attracted a great attention because of their unique properties and promising applications in integrated optoelectronic devices. Being layered materials, they can be stacked vertically to fabricate artificial van der Waals lattices, which offer unique opportunities to tailor the electronic and optical properties. The integration of TMD heterostructures in planar microcavities working in strong coupling regime is particularly important to control the light-matter interactions and form robust polaritons, highly sought for room temperature applications. Here, we demonstrate the systematic control of the coupling-strength by embedding multiple WS2 monolayers in a planar microcavity. The vacuum Rabi splitting is enhanced from 36 meV for one monolayer up to 72 meV for the four-monolayer microcavity. In addition, carrying out time-resolved pump-probe experiments at room temperature we demonstrate the nature of polariton interactions which are dominated by phase space filling effects. Furthermore, we also observe the presence of long-living dark excitations in the multiple monolayer superlattices. Our results pave the way for the realization of polaritonic devices based on planar microcavities embedding multiple monolayers and could potentially lead the way for future devices towards the exploitation of interaction-driven phenomena at room temperature.

All-Optical Control of Rotational Exciton Polaritons Condensate in Perovskite Microcavities

Exciton polariton condensation is a macroscopic quantum state that can be efficiently controlled by an external field through a nonlinear interaction. In an annular potential landscape, a rotational polariton flow with different orbit indexes can be created spontaneously. Control of their superposition states with symmetry broken is of fundamental interest for exotic quantum states. By adopting the nonresonant ring-shaped pumping in a planar perovskite microcavity, we demonstrate the linear coupled counter-rotating polariton states with ordered phase changes and a vortex pairs-petal state at the condensed threshold. The azimuthal indices and inherent flowing velocity can be well controlled by the diameter of the pumping ring and the detuning energy. At high pump density, the petal state becomes unstable and a single vortex generates, indicating the role of the polariton–polariton interaction and exciton depletion in controlling the superposition of the rotational polariton flow. Broken cylindrical symmetry is realized by a pumping ring with radial slots and the consequent dark soliton. An additional phase jump and fractional orbit index of polariton rotation can thus be obtained. Our results suggest the efficient all-optical control of rotational polariton flow and their superposition states with a flexible diameter and a broken cylindrical symmetry at room temperature, which is promising for practical polaritonic circular current-based applications with topological and chiral properties.

Triple Threshold Transitions and Strong Polariton Interaction in 2D Layered Metal-Organic Framework Microplates.

Room-temperature interaction between light-matter hybrid particles such as exciton-polaritons under extremely low-pump plays a crucial role in future coherent quantum light sources. However, the practical and scalable realization of coherent quantum light sources operating under low-pump remains a challenge because of the insufficient polariton interaction strength. Here, at room temperature, a very large polariton interaction strength is demonstrated, g≈ 128 ± 21 µeV µm2 realized in a 2D nanolayered metal-organic framework (MOF). As a result, a polariton lasing at an extremelylow pump fluence of P1 ≈ 0.01 ± 0.0015 µJ cm-2 (first threshold) is observed. Interestingly, as pump fluence increases to P2 ≈ 0.031 ± 0.003 µJ cm-2 (second threshold), a spontaneous transition to a polariton breakdown region occurs, whichhas notbeen reported before. Finally, an ordinary photon lasing occurs at P3 ≈ 0.11 ± 0.077 µJ cm-2 (third threshold), or above. These experiments and the theoretical model reveal new insights into the transition mechanisms characterized by three distinct optical regions. This work introduces MOF as a new type of quantum material, with naturally formed polariton cavities, thatis a cost-effective and scalable solution to build microscale coherent quantum light sources and polaritonic devices.

Tamm‐Plasmon Exciton‐Polaritons in Single‐Monolayered CsPbBr3 Quantum Dots at Room Temperature

AbstractConstructing polaritonic devices in monolithic, ultra‐compact photonic architectures with monolayer‐featured exciton‐emitters is decisive to exploit the coherent superposition between entangled photonic and excitonic eigenstates for potential realizations of optical nonlinearities, macroscopic condensations, and superfluidity. Here, a feasible strategy for exciton‐polariton formations is demonstrated by implementing a Tamm‐plasmon (TP) polaritonic device with the active material composed of single‐monolayered perovskite (CsPbBr3) quantum dots (QDs). The metallic character of the TP configuration is able to concentrate its resonance mode into a confined region beyond the diffraction limit, which highly overlaps, both spatially and spectrally, with the single‐monolayered CsPbBr3 QDs embedded inside. The mode volume of the device is hence reduced dramatically, leading to an enhanced light–matter coupling strength for the polaritonic emission at room temperature. In particular, it is found that the dispersion relation of the TP polaritonic device is tunable by detuning the excitonic and photonic eigenmodes and that the polariton–polariton interaction energy is strongly dependent on the polariton's spin state. The presented strategy is a determinant step toward the realization of strong light–matter coupling and polariton spintronics in the CsPbBr3 QDs with a single‐monolayered feature.

Two-dimensional exciton-polariton interactions beyond the Born approximation

We present a many-body theory for the interactions of two-dimensional exciton-polaritons beyond the Born approximation. Taking into account Gaussian quantum fluctuations via the Bogoliubov theory, we find that the exciton-exciton scattering is strongly renormalized by the light-matter coupling and acquires an inverse logarithmic dependence on the lower polariton energy. As a result, the polariton interaction strength may be enhanced at red photon-exciton detuning when the exciton-exciton scattering length is large. We also derive the exact Tan relations for exciton-polaritons, calculate Tan's contact coefficient and find an even more significant enhancement. Our predictions may provide a qualitatively correct guide for studies of exciton and polariton nonlinearities and suggest a route to achieving strongly nonlinear polariton gases.

Spatial shifts of reflected light beam on black phosphorus/hexagonal boron nitride structure

We examined Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of the reflective beam from the hexagonal boron nitride (hBN) covered by black phosphorus (BP) layers, where the BP layers are rotated by an angle with respect to the incident plane. The interaction of phonon polaritons in hBN and plasmon polaritons in BP, as well as the structure surface and interface between the two media determines the two shifts. In the common frequency–response range of the BP and hBN, the GH- and IF-shifts can be very large in the vicinity of epsilon-near-zero (ENZ) for a linearly-polarized incidence. The GH-shift can be continuously tuned from positive to negative or even to zero at a fixed frequency by adjusting the electron density and anisotropic axis-orientation of the BP. Another fascinating phenomenon is that the IF-shift can be not only excited by the linearly-polarized incidence but also greatly improved, even up to -156λ0. These conclusions are applicable to the other 2D anisotropic materials, which will become a guidance of new polarization-dependent, anisotropic optoelectronics devices.

Rydberg polaritons in ReS2 crystals.

Rhenium disulfide belongs to group VII transition metal dichalcogenides (TMDs) with attractive properties such as exceptionally high refractive index and remarkable oscillator strength, large in-plane birefringence, and good chemical stability. Unlike most other TMDs, the peculiar optical properties of rhenium disulfide persist from bulk to the monolayer, making this material potentially suitable for applications in optical devices. In this work, we demonstrate with unprecedented clarity the strong coupling between cavity modes and excited states, which results in a strong polariton interaction, showing the interest of these materials as a solid-state counterpart of Rydberg atomic systems. Moreover, we definitively clarify the nature of important spectral features, shedding light on some controversial aspects or incomplete interpretations and demonstrating that their origin is due to the interesting combination of the very high refractive index and the large oscillator strength expressed by these TMDs.

Strong photon interactions from weakly interacting particles

The hybridization of light and matter excitations in the form of polaritons has enabled major advances in understanding and controlling optical nonlinearities. Entering the quantum regime of strong interactions between individual photons has however remained challenging since the strength of achievable polariton interactions is typically limited by the available interactions in the material. Here, we investigate collisions between dark-state polaritons in three-level systems and discover a resonant process that yields effective interactions, which are much larger than the underlying interaction between their matter constituents. We systematically investigate the underlying mechanism and demonstrate a substantial enhancement of polariton interactions by several orders of magnitude. This suggests a promising approach to quantum nonlinear optics in a range of physical settings, from atomic gases to excitons in semiconductors and two-dimensional bilayer materials.