New quantum trick without electron confinement

When designing nanostructures quantum confinement only allows certain energy levels for electrons, but researchers have observed for the first time an electron energy pattern in a system that does not confine them

A research group of IMDEA Nanoscience, the Autonomous University of Madrid and the Institute of Materials Science of Madrid (ICMM-CSIC) has for the first time found experimental evidence that one-dimensional networks of nanometric periodicity can interact with the electrons of a two-dimensional gas , spatially separating their different wavelengths by a process called Bragg diffraction.

This phenomenon is known for the propagation of waves in general and is responsible for the iridescent coloration observed when looking at the surface of a CD with visible light. Due to the wave-corpuscle duality of quantum mechanics proposed by De Broglie in 1924, electrons also exhibit wave behavior and, therefore, diffraction phenomena.

In fact, the observation that low-energy free electrons undergo diffraction processes by interacting with ordered networks of atoms on the surfaces of solids was the first experimental evidence of the wave-corpuscle duality.

In addition, the two-dimensional electrons linked to the surface of the solids present a wave phenomenology that could be directly visualized for the first time in the 90s by means of the application of tunneling microscopy techniques. However, the phenomenon of Bragg diffraction in these systems had not been observed to date.

In their study, which appears today on the cover of the journal Physical Review Letters, the group led by Roberto Otero has built the nanometric periodic diffraction network through the self-assembly of organic molecules on a copper surface. The observation, by means of low-temperature tunneling microscopy, of the standing waves produced by the interference between the surface electrons that affect the diffraction network and those that are reflected by it, has allowed them to find experimental evidence of the processes of Bragg diffraction.

Furthermore, researchers have found that their results not only reflect the phenomenon of diffraction, but also that electrons prefer to interact with the network in a way that reverses the incident direction. By considering these two conditions simultaneously, the researchers argue that there is a discretization of the energy levels of electrons similar to that which occurs when electrons are spatially confined.

This process of discretization of energy levels by confinement is one of the main characteristics of quantum mechanics that finds multiple applications in Nanoscience and Nanotechnology, and currently allows to control the optical and electronic properties of nanometric systems. The results described in the article, therefore, can open new ways to manufacture devices and materials with quantum effects, without the need to confine the electrons.

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