Exploring the limits of the combination of light and matter on the nanoscale

A metasurface of a split ring resonator partially overlaid with a 3D colormap showing a simulated electric field distribution. High momentum magnetoplasmons lead to the destruction of polaritons (blue spheres with red photon energy). Credit: U. Senica, ETH Zurich

The interaction of light and matter involves a surprisingly wide range of phenomena, from photosynthesis to the fascinating colors of rainbows and butterfly wings. These symptoms can be diverse, but they involve very weak light-substance binding. In essence, light interacts with the material system, but its basic properties do not change. However, systems artificially designed to maximize the binding of light and matter experience a distinctly different set of phenomena. Next, an interesting quantum state, which is neither light nor matter, but a hybrid of the two, can emerge. Such a state is very interesting not only from a basic point of view, but also to create new features, for example to allow interactions between photons. The strongest bond ever is achieved with a semiconductor material confined in a small photonic cavity. In these devices, smaller cavities usually increase coupling. However, even if the related manufacturing challenges can be addressed, the approach pushes the fundamental physical limits, as reported in a paper published today by a team led by Professors Giacomo Scalari and Jérôme Faist at the Quantum Electronics Institute. I’m trying to face you. Nature photonics.. With this research, they set a quantitative limit on the miniaturization of such nanophotonic devices.

From strength to strength …

Over the last 40 years, various platforms have been developed to achieve strong bonds between light and matter. Among them, the one experimentally pioneered by the Faist group Scalari stands out in that it provides one of the strongest photomaterial bonds achieved on all platforms, almost continuously since 2011. increase. Importantly, in the process of setting new records, they reached a “super-powerful” regime. There, the binding of light and matter is comparable to the associated energy of the unbound matter system, providing access to a wealth of new phenomena.

At the heart of their recording setup platform is the so-called metal split ring resonator (see figure), where the electromagnetic field is localized to a very small volume, much lower than the wavelength of light (usually terahertz (THz) radiation). It can be localized. -Involvement. The micrometer-sized gaps in these resonators contain semiconductor quantum wells with suitable electronic properties that act as material systems. The natural route to increase the coupling between the excitation of the quantum well and the light confined in the resonator is to reduce the width of the gap (d in the figure). However, how powerful the coupling can be designed this way remains an open question.

… But within limits

Dr. Shima Rajabari Scalari and Faist’s group students have done this theoretically and experimentally, thanks to the quantum wells grown by senior scientist Mattias Beck and the theoretical work by Simone DeLiberato and Erika Cortese of the University of Southampton (UK). The basic physical limits of sub-wavelength confinement in a system. The team has found that it is: Electromagnetic field Concentrates on smaller volumes, and at some point the very nature of the hybrid state of light and matter (called polaritons in these cases) begins to change. This fundamental change in polaritonics characteristics prevents further increases in bond strength.


Scanning electron microscope (SEM) image of a unit cell containing a split ring resonator with a gap of d = 250 nm. Credit: S. Rajabali et al. Doi: 10.1038 / s41566-021-00854-3, Nature photonics (2021)

This limitation is not a distant scenario. With state-of-the-art nanophotonic devices, there are already signs of this paradigm shift. It just didn’t have a solid understanding of the underlying reason. This gap is currently being filled by Rajabali et al. The newly developed framework also applies not only to the specific devices studied, but also to other nano-optical systems, such as those based on graphene or transition metal dichalcogenides (TMD), and cavity geometries other than split rings. May apply. Resonator. Thus, new research should provide general quantitative limits for the binding of light and matter.

Go non-local

To explore the limits of increasing the bond between light and matter by reducing the sub-wavelength volume in which light is trapped, the team developed a theoretical framework and tested its predictions experimentally and in computer simulations. An important finding was the appearance of non-local effects on the smallest length scale considered (examining devices with gaps up to 250 nanometers wide). Below the critical length scale, the carriers are provided with large in-plane momentum, so that the tightly confined light field in the resonator is not only in the bound electronic state of the quantum well, but also in the quantum well. High momentum excitation due to known two-dimensional plasmon dispersion. This opens up new loss channels and ultimately changes the way light and matter interact in these nanophotonic devices.

Rajabali et al. Argue that this transformation into a regime dominated by the nonlocality of polaritonics causes phenomena that cannot be reproduced by classical and linear quantum theory commonly used to model the interaction of light and matter. is showing. In other words, you can rest assured that there are many things that have yet to be explored in the fascinating areas of light-matter interaction.

Researchers form super-strong bonds between photons and atoms

For more information:
Shima Rajabali et al, Polaritonics nonlocality in the interaction of light and matter, Nature photonics (2021). DOI: 10.1038 / s41566-021-00854-3

Quote: Https: // on nanoscale (August 9, 2021) obtained on August 9, 2021 Investigation of the limits of photomaterial binding

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Exploring the limits of the combination of light and matter on the nanoscale

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