Amit Dhawan

Abstract:

Controlling nanoparticle assembly in soft matter is an important objective in materials science and technology. Cholesteric liquid crystals (CLCs) constitute an exceptional template for this purpose, guiding nanoparticles into complex, organized superstructures. However, achieving large-scale superstructures and understanding the interplay of the governing forces remain a challenge. Here, we demonstrate the precise localization of gold nanoparticle (AuNP) monolayers within the modulated texture of a polymer-stabilized CLC. Using optical, electron, and atomic force microscopy combined with Landau-de Gennes energy simulations, we show and explain how AuNPs self-assemble into large-scale arch textures that replicate the underlying CLC undulations. The organization is dictated by a balance between the mitigation of elastic distortions in the CLC and the anchoring conditions imposed by the AuNP monolayer. This balance positions the nanoparticles in valleys, slightly displaced from the most elastically distorted regions, just below the air interface. This specific localization appears to be associated with a less tilted easy axis at the CLC-AuNP interface compared to nematic films, resulting in reduced local hexagonal ordering within the AuNP monolayers. Our work provides design principles for controlling nanoparticle assemblies across multiple length scales, from macroscopic architectures to nanoscale order, by exploiting the coupling between liquid crystal elasticity and surface anchoring.

Abstract:

Ultranarrow bandwidth single-photon sources operating at room-temperature are of vital importance for viable optical quantum technologies at scale, including quantum key distribution, cloud-based quantum information processing networks, and quantum metrology. Here we show a room-temperature ultranarrow bandwidth single-photon source generating single-mode photons at a rate of 5 MHz based on an inorganic CsPbI₃ perovskite quantum dot embedded in a tunable open-access optical microcavity. When coupled to an optical cavity mode, the quantum dot room-temperature emission becomes single-mode, and the spectrum narrows down to just ∼1 nm. The low numerical aperture of the optical cavities enables efficient collection of high-purity single-mode single-photon emission at room-temperature, offering promising performance for photonic and quantum technology applications. We measure 94% pure single-photon emission in a single-mode under pulsed and continuous-wave (CW) excitation.