New materials carry current without heating up

January 31, 2017 // By Nick Flaherty
Researchers have discovered two very different new materials that can handle current without heating up, enabling advances in power system, sensor and lighting design.

Researchers at Duke and the University of California, Berkeley, have found that vanadium dioxide can conduct electricity without heating up, allowing significant advances in heat pump and power supply component design.

Other electrical engineers at Duke University have created the world's first electromagnetic metamaterial made without any metal using boron-doped silicon. The device's ability to absorb electromagnetic energy without heating up has direct applications in imaging, sensing and lighting.

For most metals, the Wiedemann-Franz Law states that good conductors of electricity are also good conductors of heat. The researchers at Duke and Berkeley used simulations and X-ray scattering experiments on VO 2 nanobeams (shown above) to show the proportion of thermal conductivity attributable to the vibration of the material’s crystal lattice, called phonons, and to the movement of electrons was ten times smaller than what would be expected from the Wiedemann-Franz Law.

 “This was a totally unexpected finding,” said Junqiao Wu, a physicist at Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of materials science and engineering, working with Olivier Delaire at DOE’s Oak Ridge National Laboratory and an associate professor at Duke University. “It shows a drastic breakdown of a textbook law that has been known to be robust for conventional conductors. This discovery is of fundamental importance for understanding the basic electronic behaviour of novel conductors. “The electrons were moving in unison with each other, much like a fluid, instead of as individual particles like in normal metals,” he said.

The amount of electricity and heat that vanadium dioxide can conduct is tunable by mixing it with other materials. When the researchers doped single crystal vanadium dioxide samples with the metal tungsten, they lowered the phase transition temperature at which vanadium dioxide becomes metallic. At the same time, the electrons in the metallic phase became better heat conductors. This enabled the researchers to control the amount of heat that vanadium dioxide can dissipate by switching its phase from insulator to