A new way to combine two different states of matter

Photon-phonon breakthrough.

Scientists at City College of New York have created a new way to combine two different states of matter. Scientists combined topological photons—light with lattice vibrations, also known as phonons, using this new approach. Doing so, they were able to manipulate their propagation in a robust and controllable way.

Scientists used topological photonics, an emergent direction in photonics that leverages fundamental ideas of the mathematical field of topology about conserved quantities—topological invariants—that remain constant when altering parts of a geometric object under continuous deformations.

The topological properties give photons helicity when photons spin as they propagate, prompting exciting and surprising properties, like robustness to defects and unidirectional propagation and interfaces between topologically particular materials. Because of communications with vibrations in crystals, these helical photons would then be utilized to channel infrared light alongside vibrations.

Alexander Khanikaev, a lead author and physicist with affiliation in CCNY’s Grove School of Engineering, said, “We coupled helical photons with lattice vibrations in hexagonal boron nitride, creating a new hybrid matter referred to as phonon-polaritons. It is half light and half vibrations. Since infrared light and lattice vibrations are associated with heat, we created new channels to propagate light and heat together. Typically, lattice vibrations are very hard to control and guiding them around defects, and sharp corners were impossible before.”

This work has a wide range of implications. It could be used to advance Raman Spectroscopy. In addition, it holds promise for vibrational spectroscopy— also known as infrared spectroscopy.

Dr. Sriram Guddala, a postdoctoral researcher in Prof. Khanikaev’s group and the first author of the manuscript, said“We can create channels of arbitrary shape for this form of hybrid light and matter excitations to be guided along within a two-dimensional material we created.”

“This method also allows us to switch the direction of propagation of vibrations along these channels, forward or backward, simply by switching polarizations handedness of the incident laser beam. Interestingly, as the phonon-polaritons propagate, the vibrations also rotate along with the electric field. This is an entirely novel way of guiding and rotating lattice vibrations, which also makes them helical.”

The new method of combining two states of matter can also implement directional radiative heat transfer, a form of energy transfer during which heat is dissipated through electromagnetic waves.

Journal Reference:
  1. S. Guddala, F. Komissarenko et al. Topological phonon-polariton funneling in midinfrared metasurfaces. DOI: 10.1126/science.abj5488

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