First "Quantum Photonic Crystal" in Graphene

Sai Swaroop Sunku, a PhD student in the department of applied physics and applied mathematics, is the lead author of a study, “Photonic crystal for nano-light in moiré graphene superlattices,” conducted in the lab of Physics Professor Dmitri Basov. Published in Science, the paper examines surface plasmons, or nano-light, which are hybrids of light (photons) and electrons in graphene.

Since the 1980s, scientists have been trying to manipulate plasmons to build smaller and faster interfaces between the transistors in computers and the fiber optic cables that carry data. Plasmons could also be used to transfer data on a chip at low power with little energy loss.

Studies done over the past five years, including in the labs of Basov, Mechanical Engineering Professor Jim Hone, and others at Columbia, have shown that plasmons in graphene show great promise for such applications because they are much smaller than actual light waves and can travel long distances. But even though the small size of the graphene plasmons is what scientists want for applications such as data transfer, it has been extremely challenging to make structures small enough to manipulate the nanolight.

Sunku and his team are the first to make a “quantum photonic crystal” in graphene, a structure that can control and direct the nano-light using quantum effects. More importantly, their approach avoids the complications of making tiny structures.

The researchers discovered that they could enhance the plasmonic properties of graphene by introducing and then rotating a second graphene layer so that there is a slight angle between the atomic registry of the layers. Twisting these layers forms a moiré pattern with confined conducting channels that reflect the plasmons in a specific, tunable way. The size of this moiré pattern can be made as small as necessary simply by changing the twist angle between the layers. Thus, by controlling the structure of the pattern, the team was able to create a pathway for a nanophotonic platform that can be used for data transfer on a chip and perhaps even computation.

The team is now running more experiments at low temperatures, trying to observe novel effects such as one-dimensional plasmons that are also predicted to occur in this system.