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Experimental study of plasmon polaritons in topological insulators and Weyl Semi-Metals.

Periodic Reporting for period 1 - TOPLASMON (Experimental study of plasmon polaritons in topological insulators and Weyl Semi-Metals.)

Reporting period: 2019-05-01 to 2021-04-30

Confining light to the smallest possible volume has been a long-standing challenge for researchers. First, because it contributes to the understanding of optics and of how light behaves. Second, because confining light “concentrates” it – it makes light interact much more strongly with matter than it would otherwise. This accelerates various emission\absorption processes, with potential applications ranging from quantum computing to chemical sensing. In its extreme, strongly confined light can completely hybridize with matter (atoms, molecules) and create new phases of matter which do not exist otherwise.

However, so far, the quest to make smaller and smaller cavities has also faced a fundamental limitation – powerful optical absorption that occurs on the nanoscale and dramatically reduces cavity performance. Various approaches have been considered by researchers to reduce to size of cavities without increasing absorption, but so far it has not been possible to create cavities that are simultaneously small and high performing. Succeeding to do so is an important step towards realizing new applications and new and fundamentally interesting states of matter.
The roots of this project arose from accidental observation of the interaction of confined modes of light with the environment. Specifically, we noticed that light confined in a certain thin (almost 2D) material is strongly influenced by the presence of a metallic substrate below it. Building on this observation, we have developed an indirect way to define an extremely small cavity for light. Because it is indirect, the material inside the cavity remains pristine and the role of absorption is much less significant than in any previous cavity design.

Further examination revealed a major surprise – this indirect confinement mechanism was working dramatically better than expected. Bewilderingly, the cavities were performing better than we believed they should. Through extensive investigation using both theoretical models and experimental study, we realized the origin of this result is tied to an old and beautiful idea in physics called “bound modes in continuum”. This idea was first raised by the Hungarian-American physicist Wigner in 1929 and studied further in modern optical physics. Previously, confinement based on bound modes in continuum was not thought possible on the nanoscale. Indeed, our work expands on the basic understanding of bound in continuum states, of when they can occur and how.
These combined theoretical and experimental results are of prime interest to the scientific community, as the strong concentration of light implies an extremely large enhancement of light-matter interaction. Specifically, the cavities we obtain show quality factors (the common measure of the performance of a cavity) larger than 100, compared with a quality factor on the order of 10 or less which was achieved in any previous study of similar sized cavities. This is a milestone achievement in nanocavity research, as well as in the study of bound in continuum physics.
As such, they are currently being reviewed in a top tier journal and accepted for presentation in important conferences (CLEO Europe 2021, LEES 2021). Further dissemination to the general public will take place in the form of a traditional press release and a short youtube video oriented at the general public.
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