Electrons in graphene appear for the first time to behave like a liquid, potentially leading to devices that can efficiently convert heat to electricity and chips that can precisely model the behavior of black holes and high-energy celestial objects.
Since it was discovered 10 years ago, graphene has been hailed as a wonder material: extremely light, strong, hard and among the most conductive items on Earth. The challenge, however, is studying the unique properties of this one-atom-thick material.
Publishing their findings in the journal Science, researchers from Harvard and Raytheon BBN Technology used high-purity graphene and observed for the first time that its charged particles behave like liquid with relativistic mechanisms. Instead of avoiding each other, the electrons collide 10 trillion times per second – a never-before-seen phenomenon in ordinary metal.
The team led by Professor Philip Kim isolated an ultra-clean graphene by sandwiching the sheet between layers of hexagonal boron nitride, an insulating and transparent crystal known for its similar atomic structure with graphene.
“If the graphene is on top of something that's rough and disordered, it's going to interfere with how the electrons move,” says first author and graduate student Jesse Crossno, emphasizing the importance of preventing interference coming from the environment, hence the crystal serves as protection.
The team then established a “thermal soup” of positively and negatively charged particles on the surface, observing how they flowed as thermal and electric currents. They found that when the strongly performing particles in graphene were electrically driven, they behaved like water, one that could be described in terms of hydrodynamics.
“[We] could see the conserved energy as it flowed across many particles, like a wave through water,” recalls Crossno.
The two-dimensional, honeycomb structure of high-purity graphene forced the charged particles to move along the same paths and often collide. This forms the Dirac fluid, a strongly interacting and quasi-relativistic plasma.
Co-author Andrew Lucas deemed their work the first model of “relativistic hydrodynamics in a metal,” where graphene demonstrated the physics found in studying black holes and the like.
The results then make it possible for a graphene-based chip to be used for next-generation, ultra-thin electronic devices, as well as for analyzing the quantum physics taking place in bodies in the universe.
In the consumer products arena, graphene could help build thermoelectric tools and devices that could convert heat to electricity and vice versa with little energy lost.
For instance, lightweight circuitry incorporated in clothing could turn body heat into our smartphones’ much-needed charge.
