Newsroom

June 11, 2021

A Spatiotemporal Symphony of Light

Single-layer materials, alternatively known as 2D materials, are in themselves novel materials, solids consisting of a single layer of atoms. Graphene, the first 2D material discovered, was isolated for the first time in 2004, an achievement that garnered the 2010 Nobel Prize. Now, for the first time, Technion scientists show how pulses of light move inside these materials. Their work entitled “Spatiotemporal Imaging of 2D Polariton Wavepacket Dynamics Using Free Electrons,” was published in Science and authored by Yaniv Kurman, Raphael Dahan, Kangpeng Wang, Michael Yannai, Yuval Adiv, Ori Reinhardt, led by Prof. Ido Kramier from Technion, Hanan Herzig and ICREA Prof. Frank H. L. Koppens from ICFO, Luiz H. G. Tizei, Steffi Y. Woo, Mathieu Kociak from Université Paris Sud, and Jiahan Li, and James H. Edgar from Kansas State University.

Light moves through space at 300,000 km/s. Moving through water or through glass, it slows down by a fraction. But when moving through certain few-layers solids, light slows down almost a thousand-fold. This occurs because the light makes the atoms of these special materials vibrate to create sound waves (also called phonons), and these atomic sound waves create light when they vibrate. Thus, the pulse is actually a tightly bound combination of sound and light, called “phonon-polariton”. Lit up, the material “sings.”

The scientists shone pulses of light along the edge of a 2D material, producing in the material the hybrid sound-light waves. Not only were they able to record these waves, but they also found the pulses can spontaneously speed up and slow down. Surprisingly, the waves even split into two separate pulses, moving at different speeds.