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We have designed and realized a three-dimensional invisibility-cloaking structure operating at optical wavelengths based on transformation optics. Our blueprint uses a woodpile photonic crystal with a tailored polymer filling fraction to hide a bump in a gold reflector. We fabricated structures and controls by direct laser writing and characterized them by simultaneous high-numerical-aperture, far-field optical microscopy and spectroscopy. A cloaking operation with a large bandwidth of unpolarized light from 1.4 to 2.7 micrometers in wavelength is demonstrated for viewing angles up to 60°.

Nanotechnology enables in principle a precise mapping from design to device but relied so far on human intuition and simple optimizations. In nanophotonics, a central question is how to make devices in which the light-matter interaction strength is limited only by materials and nanofabrication. Here, we integrate measured fabrication constraints into topology optimization, aiming for the strongest possible light-matter interaction in a compact silicon membrane, demonstrating an unprecedented photonic nanocavity with a mode volume of V  ~ 3 × 10 −4   λ 3 , quality factor Q  ~ 1100, and footprint 4  λ 2 for telecom photons with a λ  ~ 1550 nm wavelength. We fabricate the cavity, which confines photons inside 8 nm silicon bridges with ultra-high aspect ratios of 30 and use near-field optical measurements to perform the first experimental demonstration of photon confinement to a single hotspot well below the diffraction limit in dielectrics. Our framework intertwines topology optimization with fabrication and thereby initiates a new paradigm of high-performance additive and subtractive manufacturing. Here, the authors integrate measured fabrication constraints in topology optimization to design a highly optimized dielectric nanocavity. The theoretically predicted confinement of light below the diffraction limit is confirmed by near- and far-field spectroscopy.

Only a few of the vast range of potential two-dimensional materials (2D) have been isolated or synthesised to date. Typically, 2D materials are discovered by mechanically exfoliating naturally occurring bulk crystals to produce atomically thin layers, after which a material-specific vapour synthesis method must be developed to grow interesting candidates in a scalable manner. Here we show a general approach for synthesising thin layers of two-dimensional binary compounds. We apply the method to obtain high quality, epitaxial MoS 2 films, and extend the principle to the synthesis of a wide range of other materials—both well-known and never-before isolated—including transition metal sulphides, selenides, tellurides, and nitrides. This approach greatly simplifies the synthesis of currently known materials, and provides a general framework for synthesising both predicted and unexpected new 2D compounds. The scalable synthesis of 2D materials critically relies on finding appropriate vapour-phase metal precursors and careful fine-tuning of growth parameters. Here, the authors instead use solid elemental precursors and a single recipe to demonstrate a general approach for synthesising thin epitaxial layers of 20 different 2D binary compounds, including transition metal sulphides, selenides, tellurides, and nitrides.

Hexagonal boron nitride (hBN), a two-dimensional (2D) material, garners interest for hosting bright quantum emitters at room temperature. While crystallographic defects are widely believed to be the source of these emitters, their exact nature, especially for visible frequencies, remains debated. Carbon impurities are frequently implicated, though their precise role is unclear, and extrinsic organic molecules at the hBN-substrate interface have also been proposed as contributors. In this study, we systematically explore the formation of luminescent emitters through irradiation engineering. Our results confirm that low-energy oxygen irradiation followed by annealing is key to forming visible quantum emitters in hBN. Notably, post-annealing in carbon-rich atmospheres significantly increases emitter density, reinforcing carbon’s potential role. We also find that hBN crystallographic quality influences emitter generation, with low-quality hBN producing nearly 20 percent more emitters than high-quality samples. While the formation of extrinsic organic molecules during high-temperature annealing cannot be ruled out, crystallographic defects formed during irradiation are central to emitter creation. We infer that these defects may promote the formation of few-atom luminescent centers and serve as molecular pinning sites. Our systematic study and findings advance the understanding of the formation of visible frequency quantum emitters in hBN.

We study the collective photon decay of multiple quantum emitters embedded in a thin high-index dielectric layer such as hexagonal boron nitride (hBN), with and without a metal substrate. We first explore the significant role that guided modes including surface plasmon modes play in the collective decay of identical single-photon emitters (super- and subradiance). Surprisingly, on distances relevant for collective emission, the guided or surface-plasmon modes do not always enhance the collective emission. We identify configurations with inhibition, and others with enhancement of the dipole interaction due to the guided modes. We interpret our results in terms of local and cross densities of optical states. In the same structure, we show a remarkably favorable configuration for enhanced Förster resonance energy transfer between a donor and acceptor in the dielectric layer on a metallic substrate. We compare our results to theoretical limits for energy transfer efficiency.

Moiré superlattices in van der Waals heterostructures represent a highly tunable quantum system, attracting substantial interest in both many-body physics and device applications. However, the influence of the moiré potential on light-matter interactions at room temperature has remained largely unexplored. In our study, we demonstrate that the moiré potential in MoS 2 /WSe 2 heterobilayers facilitates the localization of interlayer exciton (IX) at room temperature. By performing reflection contrast spectroscopy, we demonstrate the importance of atomic reconstruction in modifying intralayer excitons, supported by the atomic force microscopy experiment. When decreasing the twist angle, we observe that the IX lifetime becomes longer and light emission gets enhanced, indicating that non-radiative decay channels such as defects are suppressed by the moiré potential. Moreover, through the integration of moiré superlattices with silicon single-mode cavities, we find that the devices employing moiré-trapped IXs exhibit a significantly lower threshold, one order of magnitude smaller compared to the device utilizing delocalized IXs. These findings not only encourage the exploration of many-body physics in moiré superlattices at elevated temperatures but also pave the way for leveraging these artificial quantum materials in photonic and optoelectronic applications. The authors observe that the atomic reconstruction in MoS 2 /WSe 2 heterobilayers with large lattice mismatch results in the most significant periodic strain distribution, contributing to the effective localisation of excitons within moiré potential traps at room temperature.

We study the surface plasmon (SP) resonance energy of isolated spherical Ag nanoparticles dispersed on a silicon nitride substrate in the diameter range 3.5–26 nm with monochromated electron energy-loss spectroscopy. A significant blueshift of the SP resonance energy of 0.5 eV is measured when the particle size decreases from 26 down to 3.5 nm. We interpret the observed blueshift using three models for a metallic sphere embedded in homogeneous background material: a classical Drude model with a homogeneous electron density profile in the metal, a semiclassical model corrected for an inhomogeneous electron density associated with quantum confinement, and a semiclassical nonlocal hydrodynamic description of the electron density. We find that the latter two models provide a qualitative explanation for the observed blueshift, but the theoretical predictions show smaller blueshifts than observed experimentally.

We use mono-crystalline gold platelets with ultra-smooth surfaces and superior plasmonic properties to investigate the formation of interference patterns caused by surface plasmon polaritons (SPPs) with scattering-type scanning near-field microscopy at 521 and 633 nm. By applying a Fourier analysis approach, we can identify and separate several signal channels related to SPPs launched and scattered by the atomic force microscopy tip and the edges of the platelet. Especially at the excitation wavelength of 633 nm, we can isolate a region in the center of the platelets where we find only contributions of SPPs which are launched by the tip and reflected at the edges. These signatures are used to determine the SPP wavelength of  = 606 nm in good agreement with theoretical predictions. Furthermore, we were still able to measure SPP signals after 20 µm propagation, which demonstrates impressively the superior plasmonic quality of these mono-crystalline gold platelets.

We employ polarization tomography to characterize the modal properties of a dielectric nanocavity with sub-wavelength mode confinement. Our analysis of reflection spectra shows that the Fano-lineshape depends strongly on the polarization in a confocal configuration, and that the lineshape can be transformed into a Lorentzian-like peak for a certain polarization. For this polarization setting, the background is almost fully suppressed in a finite range of frequencies. This enables us to identify another resonance that has not yet been experimentally reported for these nanocavities. Lastly, we use symmetry-forbidden polarizations and show that, surprisingly, the modal resonance features of the system remain visible.

Coherent acoustic phonons (CAPs)—‐vibrational modes prepared in a coherent state that propagate as long‐wavelength strain waves—can dynamically modulate crystal structure and, in some cases, symmetry, offering unique opportunities for controlling material properties. We investigate CAP generation in exfoliated multilayer flakes of the alloy tungsten sulfide selenide (WS2xSe2(1−x) \\rm WS₂ₓ\\rm Se₂₍₁₋ₓ₎ , hereafter WSSe). Using high‐fluence 400 nm excitation together with ultrafast transient‐reflection spectroscopy, we track the coupled carrier‐lattice response, revealing dynamics consistent with a sequence of rapid carrier thermalization and exciton formation, phonon recycling, and photoinduced stress from prompt deformation potential and slower thermoelastic contributions that combined drive a coherent oscillation at 27 GHz. The fractional amplitude of the oscillatory component attributed to an acoustic mode in a coherent state is substantially larger in WSSe than in the parent crystals WS2 and WSe2, where the coherent contribution represents only a minor perturbation superimposed on a dominant monotonic background. This pronounced enhancement indicates that the alloy does not behave as a simple interpolation between the binary compounds, but instead exhibits an emergent optical‐acoustic response linked to chalcogen mixing. Finally, by implementing a two‐pulse excitation scheme, we demonstrate optical control of the CAP phase and amplitude, highlighting the potential of TMDC alloys to support dynamic modulation of optomechanical and acoustic responses for advanced device engineering. Coherent acoustic phonons are generated and optically controlled in bulk WSSe alloy samples using ultrafast spectroscopy. The alloy exhibits a strong coherent acoustic response, which is not an intermediate state between WS? and WSe?. Instead, a much more complex mechanism is proposed. Furthermore, two‐pulse excitation enables dynamic tuning of the phonon phase and amplitude.