A fundamental requirement for photonic technologies is the ability to control the confinement and propagation of light. Widely utilized platforms include 2D optical microcavities in which electromagnetic waves are confined between either metallic or multi-layer distributed Bragg reflector dielectric mirrors. However, the fabrication complexities of thick Bragg reflectors and high losses in metallic mirrors have motivated the quest for efficient and compact mirrors. Recently, 2D transition metal dichalcogenides hosting tightly bound excitons with high optical quality were shown as promising atomically thin mirrors (a, b). In this work, we propose and experimentally demonstrate a sub-wavelength 2D nanocavity using two atomically thin mirrors (c-f). Remarkably, we show how the excitonic nature of the mirrors enables the formation of chiral and tunable cavity modes upon the application of an external magnetic field (g). Our work establishes a new regime for engineering intrinsically chiral sub-wavelength optical cavities and opens avenues for realizing spin-photon interfaces and exploring chiral many-body cavity electrodynamics.
We investigate the optical properties of two-dimensional monolayer films of MoSe2 and WSe2 (each 0.7nm thick) assembled on SiO2/Si substrates (285nm/0.5mm thick). These films are interesting because they are direct band gap semiconductors that have large excitonic responses. However, due to numerous challenges, including the lack of a quick, contactless, and reliable method, obtaining the optical constants and exciton binding energies in-situ remains a difficult endeavor. Here, we report the optical properties based on contactless ellipsometry to retrieve the optical constants (n,k) and excitonic properties of both monolayers (MoSe2 and WSe2). The optical properties of these materials away from the exciton (~700 nm) are generally not well understood. In this work, we will explore the optical response of these films over a broad range that includes the UV/visible and near infrared (200-2000nm) in order to understand if there are other spectral regions with a strong or tunable refractive index. The current samples are intrinsic without doping. The SiO2 on the Si substrate would be used as a gate capacitor which would allow to vary the density by ~1011-1012 cm-2. These transition metal dichalcogenides (TMD) offer new possibilities for designing modern photonic and optoelectronic components.
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