arXiv subjects

Thomas Darlington

Publications and source records attributed to Thomas Darlington.

4 recordsLinked to original sources

arXiv2026

Determination of the roles of strain and tearing in single photon emission from nanoindented WSe$_2$

Single-photon emission in two-dimensional single-layer WSe2 is attractive for the on-demand generation of quantum states of light. The electronic states that are responsible for single-photon generation preferentially form in regions of localized tensile strain, enabling deterministic positioning and strain engineering. Nanoindentation of single-layer WSe2 yields controlled and reproducible deformations that generate the localized strain needed to activate the single-photon-emitting states. However, using nanoindentation both for investigating structure-property relationships and for manufacturing quantum light sources based on WSe2 is hindered by key questions on the structural integrity of the indented 2D material, the resulting strain generated, and the sub-micron location of the emitters. In this work, we study the structure of indented single-layer WSe2 using a fabrication process that inverts the indents into protruding pillars that can be probed using electron microscopy. We explicitly identify strain relaxation of the indented single-layer WSe2 due to tearing and confirm that single-photon-emitting states still form in these systems, likely at the extremities of the tear. For indents that are confirmed to be intact (i.e., not torn), we assess the ability to strain engineer the single-photon emitters. While strain does not strongly affect the emission energy or the brightness, we find that increased strain reduces the spatial density of emitters. This trend indicates that an optimal amount of strain is needed for emitter formation and/or the emitters preferentially form on the periphery of the indent. Our investigation provides insight into the most relevant structure-property relationships for using strain to engineer quantum light sources in single-layer WSe2 and other 2D semiconductors.

physics.app-ph↗

arXiv2023

Ultrastrong Light-Matter Coupling in 2D Metal-Chalcogenates

Hybridization of excitons with photons to form hybrid quasiparticles, exciton-polaritons (EPs), has been widely investigated in a range of semiconductor material systems coupled to photonic cavities. Self-hybridization occurs when the semiconductor itself can serve as the photonic cavity medium resulting in strongly-coupled EPs with Rabi splitting energies > 200 meV at room temperatures which recently were observed in layered two-dimensional (2D) excitonic materials. Here, we report an extreme version of this phenomenon, an ultrastrong EP coupling, in a nascent, 2D excitonic system, the metal organic chalcogenate (MOCHA) compound named mithrene. The resulting self-hybridized EPs in mithrene crystals placed on Au substrates show Rabi Splitting in the ultrastrong coupling range (> 600 meV) due to the strong oscillator strength of the excitons concurrent with the large refractive indices of mithrene. We further show bright EP emission at room temperature as well as EP dispersions at low-temperatures. Importantly, we find lower EP emission linewidth narrowing to ~1 nm when mithrene crystals are placed in closed Fabry-Perot cavities. Our results suggest that MOCHA materials are ideal for polaritonics in the deep green-blue part of the spectrum where strong excitonic materials with large optical constants are notably scarce.

physics.optics↗

arXiv2023

Charge and Energy Transfer Dynamics of Hybridized Exciton-Polaritons in 2D Halide Perovskites

Excitons, bound electron-hole pairs, in Two-Dimensional Hybrid Organic Inorganic Perovskites (2D HOIPs) are capable of forming hybrid light-matter states known as exciton-polaritons (E-Ps) when the excitonic medium is confined in an optical cavity. In the case of 2D HOIPs, they can self-hybridize into E-Ps at specific thicknesses of the HOIP crystals that form a resonant optical cavity with the excitons. However, the fundamental properties of these self-hybridized E-Ps in 2D HOIPs, including their role in ultrafast energy and/or charge transfer at interfaces, remain unclear. Here, we demonstrate that > 0.5 um thick 2D HOIP crystals on Au substrates are capable of supporting multiple-orders of self-hybridized E-P modes. These E-Ps have high Q factors (> 100) and modulate the optical dispersion for the crystal to enhance sub-gap absorption and emission. Through varying excitation energy and ultrafast measurements, we also confirm energy transfer from higher energy upper E-Ps to lower energy, lower E-Ps. Finally, we also demonstrate that E-Ps are capable of charge transport and transfer at interfaces. Our findings provide new insights into charge and energy transfer in E-Ps opening new opportunities towards their manipulation for polaritonic devices.

cond-mat.mes-hall↗

arXiv2021

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton-Enhanced Second Harmonic Generation

Second harmonic generation (SHG) is a nonlinear optical response arising exclusively from broken inversion symmetry in the electric-dipole limit. Recently, SHG has attracted widespread interest as a versatile and noninvasive tool for characterization of crystal symmetry and emerging ferroic or topological orders in quantum materials. However, conventional far-field optics is unable to probe local symmetry at the deep subwavelength scale. Here, we demonstrate near-field SHG imaging of 2D semiconductors and heterostructures with the spatial resolution down to 20 nm using a scattering-type nano-optical apparatus. We show that near-field SHG efficiency is greatly enhanced by excitons in atomically thin transition metal dichalcogenides. Furthermore, by correlating nonlinear and linear scattering-type nano-imaging, we resolve nanoscale variations of interlayer stacking order in bilayer WSe2, and reveal the stacking-tuned excitonic light-matter-interactions. Our work demonstrates nonlinear optical interrogation of crystal symmetry and structure-property relationships at the nanometer length scales relevant to emerging properties in quantum materials.

physics.optics↗