| 1. |
- Baranov, Denis, 1990, et al.
(författare)
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Ultrastrong coupling between nanoparticle plasmons and cavity photons at ambient conditions
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Ultrastrong coupling is a distinct regime of electromagnetic interaction that enables a rich variety of intriguing physical phenomena. Traditionally, this regime has been reached by coupling intersubband transitions of multiple quantum wells, superconducting artificial atoms, or two-dimensional electron gases to microcavity resonators. However, employing these platforms requires demanding experimental conditions such as cryogenic temperatures, strong magnetic fields, and high vacuum. Here, we use a plasmonic nanorod array positioned at the antinode of a resonant optical Fabry-Pérot microcavity to reach the ultrastrong coupling (USC) regime at ambient conditions and without the use of magnetic fields. From optical measurements we extract the value of the interaction strength over the transition energy as high as g/ω ~ 0.55, deep in the USC regime, while the nanorod array occupies only ∼4% of the cavity volume. Moreover, by comparing the resonant energies of the coupled and uncoupled systems, we indirectly observe up to ∼10% modification of the ground-state energy, which is a hallmark of USC. Our results suggest that plasmon-microcavity polaritons are a promising platform for room-temperature USC realizations in the optical and infrared ranges, and may lead to the long-sought direct visualization of the vacuum energy modification.
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| 2. |
- Munkhbat, Battulga, 1988, et al.
(författare)
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Electrical Control of Hybrid Monolayer Tungsten Disulfide-Plasmonic Nanoantenna Light-Matter States at Cryogenic and Room Temperatures
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 14:1, s. 1196-1206
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid light-matter states-polaritons-have attracted considerable scientific interest recently, motivated by their potential for development of nonlinear and quantum optical schemes. To realize such states, monolayer transition metal dichalcogenides (TMDCs) have been widely employed as excitonic materials. In addition to neutral excitons, TMDCs host charged excitons, which enables active tuning of hybrid light-matter states by electrical means. Although several reports demonstrated charged exciton-polaritons in various systems, the full-range interaction control attainable at room temperature has not been realized. Here, we demonstrate electrically tunable charged exciton-plasmon polaritons in a hybrid tungsten disulfide (WS2) monolayer-plasmonic nanoantenna system. We show that electrical gating of monolayer WS2 allows tuning the oscillator strengths of neutral and charged excitons not only at cryogenic but also at room temperature, both at vacuum and atmospheric pressure. Such electrical control enables a full-range tunable switching from strong neutral exciton-plasmon coupling to strong charged exciton-plasmon coupling. Our experimental findings allow discussing beneficial and limiting factors of charged exciton-plasmon polaritons, as well as offer routes toward realization of charged polaritonic devices at ambient conditions.
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| 3. |
- Baranov, Denis, 1990, et al.
(författare)
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Circular dichroism mode splitting and bounds to its enhancement with cavity-plasmon-polaritons
- 2020
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Ingår i: Nanophotonics. - : Walter de Gruyter GmbH. - 2192-8614. ; 9:2, s. 283-293
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Tidskriftsartikel (refereegranskat)abstract
- Geometrical chirality is a widespread phenomenon that has fundamental implications for discriminating enantiomers of biomolecules. In order to enhance the chiral response of the medium, it has been suggested to couple chiral molecules to resonant optical cavities in order to enhance the circular dichroism (CD) signal at the resonant frequency of the cavity. Here, we studied a distinctly different regime of chiral light-matter interaction, wherein the CD signal of a chiral medium splits into polaritonic modes by reaching the strong coupling regime with an optical microcavity. Specifically, we show that by strongly coupling chiral plasmonic nanoparticles to a non-chiral Fabry-Pérot microcavity one can imprint the mode splitting on the CD spectrum of the coupled system and thereby effectively shift the initial chiral resonance to a different energy. We first examined the effect with the use of analytical transfer-matrix method as well as numerical finite-difference time-domain (FDTD) simulations. Furthermore, we confirmed the validity of theoretical predictions in a proof-of-principle experiment involving chiral plasmonic nanoparticles coupled to a Fabry-Pérot microcavity.
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| 4. |
- Kücüköz, Betül, 1988, et al.
(författare)
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Boosting Second-Harmonic Generation in Monolayer Rhenium Disulfide by Reversible Laser Patterning
- 2022
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:2, s. 518-526
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Tidskriftsartikel (refereegranskat)abstract
- Active modification and control of transition metal dichalcogenides (TMDs) properties are highly desirable for next-generation optoelectronic applications. In particular, controlling one of the most important characteristics of TMDs─their crystal structure and symmetry─may open means for manipulating their optical nonlinearities and electrical transport properties. Here, we show that a monolayer ReS2, which does not have a broken inversion symmetry due to its stable 1T′-distorted phase and correspondingly shows only weak second-harmonic generation (SHG), can produce a significantly enhanced (∼2 orders of magnitude) SHG upon reversible laser patterning. This enhancement can be explained by the laser-induced transition from centrosymmetric 1T′ to noncentrosymmetric 2H-phase. This hypothesis is confirmed by polarization-resolved SHG measurements, which reveal a gradual change from the 2-fold to 6-fold symmetry profiles upon laser patterning. Additionally, we found that laser patterning of the bilayer ReS2 samples, contrary to the monolayers, leads to a substantially reduced SHG signal. This result corroborates the 1T′-to-2H laser-induced phase transition. Finally, we show that the laser-induced patterning is reversible by heat. These results open a possibility to actively and reversibly control the crystal structure of mono- and few-layer ReS2 and thus its optical and electronic properties.
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| 5. |
- Munkhbat, Battulga, 1988, et al.
(författare)
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Nanostructured Transition Metal Dichalcogenide Multilayers for Advanced Nanophotonics
- 2023
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Ingår i: Laser and Photonics Reviews. - : Wiley. - 1863-8899 .- 1863-8880. ; 17:1
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical, excitonic, mechanical, and electronic properties. Nanostructured multilayer TMDs were recently shown to be highly promising for nanophotonic applications, as motivated by their exceptionally high refractive indices and optical anisotropy. Here, this vision is extended to more sophisticated structures, such as periodic arrays of nanodisks and nanoholes with ultra sharp walls, as well as proof-of-concept all-TMD waveguides and resonators. Specific focus is given to various advanced nanofabrication strategies, including careful selection of resists for electron beam lithography and etching methods, especially for non-conductiven but relevant for nanophotonic applications substrates, such as SiO2. The specific materials studied here include semiconducting WS2, in-plane anisotropic ReS2, and metallic TaSe2, TaS2, and NbSe2. The resulting nanostructures can potentially impact several nanophotonic and optoelectronic areas, including high-index nanophotonics, plasmonics and on-chip optical circuits. The knowledge of TMD material-dependent nanofabrication parameters developed here will help broaden the scope of future applications of all-TMD nanophotonics.
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| 6. |
- Munkhbat, Battulga, 1988, et al.
(författare)
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Self-Hybridized Exciton-Polaritons in Multilayers of Transition Metal Dichalcogenides for Efficient Light Absorption
- 2019
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 6:1, s. 139-147
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal dichalcogenides (TMDCs) have attracted significant attention recently in the context of strong light–matter interaction. To observe strong coupling using these materials, excitons are typically hybridized with resonant photonic modes of stand-alone optical cavities, such as Fabry–Pérot microcavities or plasmonic nanoantennas. Here, we show that thick flakes of layered van der Waals TMDCs can themselves serve as low-quality resonators due to their high background permittivity. Optical modes of such “cavities” can in turn hybridize with excitons in the same material. We perform an experimental and theoretical study of such self-hybridization in thick flakes of four common TMDC materials: WS2, WSe2, MoS2, and MoSe2. We observe splitting in reflection and transmission spectra in all four cases and provide angle-resolved dispersion measurements of exciton-polaritons as well as thickness-dependent data. Moreover, we observe significant enhancement and broadening of absorption in thick TMDC multilayers, which can be interpreted in terms of strong light–matter coupling. Remarkably, absorption reaches >50% efficiency across the entire visible spectrum, while simultaneously being weakly dependent on polarization and angle of incidence. Our results thus suggest formation of self-hybridized exciton-polaritons in thick TMDC flakes, which in turn may pave the way toward polaritonic and optoelectronic devices in these simple systems.
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| 7. |
- Munkhbat, Battulga, 1988, et al.
(författare)
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Tunable self-assembled Casimir microcavities and polaritons
- 2021
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 597:7875, s. 214-219
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Tidskriftsartikel (refereegranskat)abstract
- Spontaneous formation of ordered structures—self-assembly—is ubiquitous in nature and observed on different length scales, ranging from atomic and molecular systems to micrometre-scale objects and living matter1. Self-ordering in molecular and biological systems typically involves short-range hydrophobic and van der Waals interactions2,3. Here we introduce an approach to micrometre-scale self-assembly based on the joint action of attractive Casimir and repulsive electrostatic forces arising between charged metallic nanoflakes in an aqueous solution. This system forms a self-assembled optical Fabry–Pérot microcavity with a fundamental mode in the visible range (long-range separation distance about 100–200 nanometres) and a tunable equilibrium configuration. Furthermore, by placing an excitonic material in the microcavity region, we are able to realize hybrid light–matter states (polaritons4–6), whose properties, such as coupling strength and eigenstate composition, can be controlled in real time by the concentration of ligand molecules in the solution and light pressure. These Casimir microcavities could find future use as sensitive and tunable platforms for a variety of applications, including opto-mechanics7, nanomachinery8 and cavity-induced polaritonic chemistry9.
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| 8. |
- Fesenko, Olean, et al.
(författare)
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Metal-graphene nanostructures for SEIRA spectroscopy
- 2020
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Ingår i: Molecular Crystals and Liquid Crystals. - : Informa UK Limited. - 1563-5287 .- 1542-1406. ; 701:1, s. 106-117
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Tidskriftsartikel (refereegranskat)abstract
- Infrared spectroscopy is widely used technique for observing bioorganic materials, but sometimes scientist have to work with small amount of investigated materials and infrared light interacts poorly with nanometric size molecules. Taking into account unique electro-optical properties of graphene and metal we demonstrated possibility to use metal-graphene nanostructures for label-free detection of thymine. It was shown that IR spectra of thymine adsorbed on the composite nanostructures, such as Au "nanostars" with graphene, is more enhanced than whenthese nanoparticles are used without graphene. The enhancement in IR absorption for complex thymine/Au/graphene depends on size of Au nanoparticlesand thymine's molecular group.
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| 9. |
- Green, Thomas D, 1984, et al.
(författare)
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Optical material anisotropy in high-index transition metal dichalcogenide Mie nanoresonators
- 2020
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Ingår i: Optica. - 2334-2536. ; 7:6, s. 680-686
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Tidskriftsartikel (refereegranskat)abstract
- Resonant optical antennas provide unprecedented opportunities to control light on length scales far below the diffraction limit. Recent studies have demonstrated that nanostructures made of multilayer transition metal dichalcogenides (TMDCs) can exhibit well-defined and intense Mie resonances in the visible to the near-infrared spectral range. These resonances are realizable because the TMDC materials exhibit very high in-plane refractive indices, in fact higher than what is found in typical high-index dielectric materials like Si orGaAs. However, their out-of-plane refractive indices are comparatively low. Here we experimentally and theoretically investigate how this unusually large material anisotropy influences the optical response of individual TMDC nanoresonators made of MoS2. We find that anisotropy strongly affects the far-field optical response of the resonators, as well as complex interference effects, such as anapole and resonant Kerker conditions. Moreover, we show that it is possible to utilize the material anisotropy to probe the vectorial nature of the nanoresonator internal near fields. Specifically, we show that Raman spectra originating from individual MoS2 nanoresonators exhibit mode-specific anisotropic enhancement factors that vary with the nanoresonator size and correlate with specific modes supported at resonance. Our study indicates that exploring material anisotropy in novel high-index dielectrics may lead to new nanophotonic effects and applications. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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| 10. |
- Haslinger, Michael J., et al.
(författare)
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Plasmon-assisted direction-and polarization-sensitive organic thin-film detector
- 2020
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 10:9, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing Bragg surface plasmon polaritons (SPPs) on metal nanostructures for the use in optical devices has been intensively investigated in recent years. Here, we demonstrate the integration of nanostructured metal electrodes into an ITO-free thin film bulk heterojunction organic solar cell, by direct fabrication on a nanoimprinted substrate. The nanostructured device shows interesting optical and electrical behavior, depending on angle and polarization of incidence and the side of excitation. Remarkably, for incidence through the top electrode, a dependency on linear polarization and angle of incidence can be observed. We show that these peculiar characteristics can be attributed to the excitation of dispersive and non-dispersive Bragg SPPs on the metal–dielectric interface on the top electrode and compare it with incidence through the bottom electrode. Furthermore, the optical and electrical response can be controlled by the organic photoactive material, the nanostructures, the materials used for the electrodes and the epoxy encapsulation. Our device can be used as a detector, which generates a direct electrical readout and therefore enables the measuring of the angle of incidence of up to 60° or the linear polarization state of light, in a spectral region, which is determined by the active material. Our results could furthermore lead to novel organic Bragg SPP-based sensor for a number of applications.
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