Topologically distinct photonic Crystals (orange and bleu) have a layer of hexagonal Boron Nitride on the top. This allows coupling of topological and lattice vibrations in order to form chiral Half-Light/Half-Vibration Excitations that can be directed along 1D channels in a robust manner. Credit: Filipp Komissarenko, Sriram Guddala
A City College of New York team discovered a novel way of combining two states of matter. Topological photonslight has been combined with lattice vibrations (also known as phonons) to control their propagation. This is the first time this has happened.
The study utilized topological photonics, an emergent direction in photonics which leverages fundamental ideas of the mathematical field of topology about conserved quantitiestopological invariantsthat remain constant when altering parts of a geometric object under continuous deformations. Number of holes is one of the most basic examples of such invariants. This makes mugs and donuts equivalent from a topological perspective. Photons are endowed with helicity by topological properties. When photons spin, they can cause unidirectional propagation between topologically different materials. These helical photons are then able to transmit infrared light and vibrations thanks to their interactions with vibrations within crystals.
This work has broad implications. It will allow researchers to improve Raman spectroscopy which is used for determining vibrational modes in molecules. This research holds promise for vibrational spectrumcopy, also known as infraredspectroscopy, which measures the interaction between infrared radiation and matter via absorption, emission, reflection. This information can be used to identify and characterize chemical compounds.
Alexander Khanikaev (lead author, physicist, affiliation in CCNY Grove School of Engineering) said, "We combined helical photons and lattice vibrations of hexagonal boron nitride to create a new hybrid matter referred as phonon-polaritons." It is half light, half vibrations. We created new channels to allow heat and infrared light to be propagated together. Lattice vibrations can be difficult to control and it was impossible to guide them around sharp corners and defects.
This new method can also be used to implement directional radiative heating transfer, which is a form energy transfer in which heat is dissipated by electromagnetic waves.
Dr. Sriram Guddala is a postdoctoral researcher in Prof. Khanikaev’s group and the first author. This method allows us to change the direction of propagation for vibrations along these channels, either forward or backward by simply switching the polarizations of incident laser beams. It is interesting that the phonon-polaritons also propagate and the vibrations rotate with the electric field. This new method of controlling and rotating lattice vibrations is helical.
The study is entitled "Topological Phonon-Politon Filtering in Midinfrared Metasurfaces" and appears in Science.
Continue reading Vibrational encountersphonon Polaritons Meet Molecules
S. Guddala and colleagues, Topological Phonon-Politon Channeling in Mid-Infrared Metasurfaces, Science (2021). www.science.org/doi/10.1126/science.abj5488 Journal information: Science S. Guddala et al, Topological phonon-polariton funneling in mid-infrared metasurfaces,(2021). DOI: 10.1126/science.abj5488