Topological Transitions in Metamaterials Offers Potential for More Efficient Solar Cells, Super Bright LEDs and Ultra-High Sensitive Sensors

A team of physicists headed by Dr. Vinod M. Menon, who is a member of The City University of New York Photonics Initiative and teaches at Queens College, has discovered a new method to manipulate light that could eventually result in more efficient solar cells, super bright LEDs, ultra-high sensitive sensors and single photon sources necessary for quantum communication protocols and quantum computers.

Science journal – Light-matter interactions can be controlled by manipulating the photonic environment. We uncovered an optical topological transition in strongly anisotropic metamaterials that results in a dramatic increase in the photon density of states—an effect that can be used to engineer this interaction. We describe a transition in the topology of the iso-frequency surface from a closed ellipsoid to an open hyperboloid by use of artificially nanostructured metamaterials. We show that this topological transition manifests itself in increased rates of spontaneous emission of emitters positioned near the metamaterial. Altering the topology of the iso-frequency surface by using metamaterials provides a fundamentally new route to manipulating light-matter interactions.

Borrowing an idea from the field of mathematical topology, the scientists have created an artificial material — called “metamaterial” — that can transform from regular dielectric (a substance like glass or plastic, which does not conduct electricity) to a medium that behaves like metal (reflects) in one direction and like dielectric (transmits) in the other. The optical properties of this metamaterial can be mapped onto a topological transformation of an ellipsoidal surface into a hyperboloid.

Topology is the mathematical field dealing with the properties of objects undergoing deformations, such as stretching and twisting. The ellipsoid and hyperboloid belong to different classes of surfaces, the former being closed (bound) and the latter being open (unbound). The topological transition from such a bound (elliptic) to an unbound (hyperbolic) surface manifests itself in the real world as a dramatic increase of light intensity inside the material.

The breakthrough optical topological transition was exploited by the research team to manipulate the propagation of light within the metamaterial. This aspect was then used by the physicists to demonstrate modification in the light emission of a nanoparticle placed in the vicinity of the metamaterial.

“While this is a fundamental work, the effect reported here in metamaterials offers the promise of multiple applications in a number of important fields,” stated Dr. Menon. “For example, it can help in enhanced light harvesting, which could result in more efficient solar cells. It may also be used to develop single photon
sources necessary for quantum communication protocols and quantum computers. Through engineering of transmission properties of these systems, and by combining them with light emitters, one may also realize super bright LEDs that would be useful for display applications.”

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