Researchers suggest a new methodology for characterizing the interaction of light with matter at atomic sizes

Courtesy: IMDEA Nanociencia.

Photonic cavities are an integral part of many modern optical devices, from laser pointers to microwave ovens. Just as we can store water in a tank and create standing waves on the surface of the water, we can limit the light in a photon resonator whose walls reflect strongly. Just as surface water waves depend on the geometry of the reservoir (shape, depth), certain optical modes can be created in the photon cavity whose properties (color and spatial intensity distribution) can be adjusted by changing the dimensions of the cavity. When the size of the cavity is very small – much less than the wavelength of the light bounding it (nanoresonator in the case of visible light) – the effect of amplification of light is created, which is so strong that it affects the electrons on the walls of the cavity. Then a mixture forms between photons and electrons, resulting in hybrid modes between light and matter, known as plasmons.

Plasmons in optical nanocavities are extremely important for many applications, such as chemical sensors which allow you to detect individual molecules or produce nanolasers that can work almost without the consumption of electric current. However, the characterization of these plasmon modes is usually very complex due to the tiny cavity size, which makes it extremely difficult to access them through external signals.

On the other hand, the tunnel effect is one of the most characteristic, mysterious, and most well-documented effects of quantum mechanics. In a tunneling process, a particle (for example, an electron) can pass through a narrow barrier (a space that separates two metals at nanometric distances), despite the fact that it does not have enough energy to overcome it. It is as if we could go from one side to the other of the Great Wall of China without jumping over it.

No matter how incredible it may seem, particles from the quantum world can do this under certain conditions. In most of these processes, the particle energy before and after the process is the same. However, in a small part of these events, a particle can abandon part of its energy, for example, by generating light, which is known as an inelastic tunneling process. Although it is well known that the properties of light emitted in an inelastic tunneling process between two metals depend on the plasmon modes existing in cavity, it also strongly depends on the energy distribution of the particles involved in the tunneling process.

Until now, it has been impossible to unequivocally distinguish between these two effects and, therefore, extract information about plasmon modes from an analysis of the light emitted by the tunneling effect.

Researchers at the University of Madrid, IMDEA Nanociencia and IFIMAC have developed a method to solve this problem by simultaneously determining the distribution of energy of tunneling electrons and the light emitted by scanning. tunnel microscope. They used the tunneling effect to create atomic-sized optical resonators and to study their optical properties, first revealing the contributions caused by energy tunnel particles from effects caused by plasmon modes in the cavity.

This work offers a new methodology for characterization. light colouredthe interaction of matter in an atomic size, and can have important technological consequences for the development of chemical sensors of individual molecules, new sources of single or interlaced photons or nanolasers that are active at extremely low pump powers.

The study was published in a prestigious journal. The bonds of nature,

Molecular Directional Plasmon Excitation

Additional Information:
Alberto Martin-Jimenez et al. Disclosure of the local radiation density of the optical states of a plasmon nanoresonator using STM, The bonds of nature (2020). DOI: 10.1038 / s41467-020-14827-7

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IMDEA Nanociencia

Researchers suggest a new methodology for characterizing the interaction of light with matter at atomic sizes (2020, March 25)
restored March 25, 2020

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