Scientists observe electrons in a metal behaving like a fluid

Graphene and its unique properties are offering scientists a new opportunity to coax divergent theories of physics into agreement.
By Brooks Hays   |   Feb. 11, 2016 at 6:57 PM

CAMBRIDGE, Mass., Feb. 11 (UPI) -- Experiments by Harvard researchers have shown electrons in a metal behaving like a liquid -- a first. The metal is graphene, and the implications of the new research are significant.

Graphene is composed of atom-thick layers of carbon with atoms organized in a honeycomb-like pattern. It is flexible, strong and conductive.

Material scientists have demonstrated graphene's many potential applications in electronics, but graphene has yet to fully deliver on its potential.

Scientists still don't entirely understand the material's basic physical properties and have struggled to efficiently produce the material without impurities.

A team of researchers at Harvard University, led by physicist Philip Kim, set out to rectify the first of those two problems by taking an in-depth look at graphene's subatomic realities. In doing so, they discovered electrons behaving in a way never before seen in a metal.

Experiments revealed fast-moving, highly energized electrons speeding across graphene's layers. Researchers liken the material's atom-thick layers to an electron superhighway.

Electrons in graphene were clocked moving at 1/300th the speed of light, and their newly recorded data suggests the material's particles are colliding ten trillion times per second.

Researchers were intrigued by graphene's fast-moving electrons, but they were most surprised by the manner in which the material's particles responded to thermal and electric currents -- which caused atoms to begin acting more like a fluid than a metal. It's a discovery that has implications for several different branches of physics.

"Instead of watching how a single particle was affected by an electric or thermal force, we could see the conserved energy as it flowed across many particles, like a wave through water," first study author Jesse Crossno, a researcher in Kim's lab at Harvard, said in a news release.

Classic physics describes most of the tangible world. Hydrodynamics, the physics of water, is a branch of classical physics. Atomic and subatomic systems are described by quantum mechanics, while scientists use relativistic physics to describe much larger systems like galaxies.

Scientists have struggled to bridge these theories together, but some topics like supernovas and black holes have required the use of both relativity and hydrodynamics.

Graphene and its unique properties are offering scientists a new opportunity to coax divergent theories of physics into agreement.

"Physics we discovered by studying black holes and string theory, we're seeing in graphene," explained study co-author Andrew Lucas, a graduate student in physics at Harvard.

Their discovery means graphene could prove useful for not just material scientists and industrial innovators, but also quantum physicists, astronomers and cosmologists.

But that's not all. Researchers also found a new way to precisely measure the thermal conductivity of graphene's atoms. By monitoring the random movements of electrons as graphene's temperature changed, scientists were able to accurately gauge thermal conductivity.

"This work provides a new way to control the rate of heat transduction in graphene's electron system, and as such will be key for energy and sensing-related applications," explained Leonid Levitov, a physics professor at the Massachusetts Institute of Technology.

"Converting thermal energy into electric currents and vice versa is notoriously hard with ordinary materials," added Lucas. "But in principle, with a clean sample of graphene there may be no limit to how good a device you could make."

The study's findings are detailed in the journal Science.

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