Gizmorama - February 1, 2017

Good Morning,

Scientists have discovered a metal that breaks the law...the Wiedemann-Franz Law. Metallic vanadium dioxide will conduct electric current without a problem, but it won't conduct heat with it. Interesting, eh?

Learn about this and more interesting stories from the scientific community in today's issue.

Until Next Time,
Erin

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Scientists discover metal that conducts electricity but not heat
BERKELEY, Calif. - Researchers have discovered a metal that fails to comply with the Wiedemann-Franz Law, the rule that suggests good conductors of electricity will also be good conductors of thermal energy.

Metallic vanadium dioxide easily carries an electric current, but fails to conduct heat as expected.

"This was a totally unexpected finding," Junqiao Wu, a professor of materials science and engineering at the University of California, Berkeley, said in a news release. "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 behavior of novel conductors."

The revelation -- detailed in the journal Science -- furthers the oddball reputation of metallic vanadium dioxide.

Previous studies showed the substance is an insulator at room temperature, but becomes a conductor once it reachers a temperature of 152 degrees Fahrenheit.

Researchers used electron scanning imagery to observe the movement of heat energy across the material. Modeling and lab experiments helped scientists determine how much heat was being carried by electrons and how much was being propagated by the vibration of the material's unique crystal lattices, or phonons.

"The electrons were moving in unison with each other, much like a fluid, instead of as individual particles like in normal metals," explained Wu. "For electrons, heat is a random motion. Normal metals transport heat efficiently because there are so many different possible microscopic configurations that the individual electrons can jump between. In contrast, the coordinated, marching-band-like motion of electrons in vanadium dioxide is detrimental to heat transfer as there are fewer configurations available for the electrons to hop randomly between."

Scientists were able to lower the threshold for vanadium dioxide's electric conductivity by mixing it with other materials, like metal tungsten. Mixing also encouraged the vanadium dioxide's electrons to carry heat more effectively.

"This material could be used to help stabilize temperature," said Fan Yang, a postdoctoral researcher at Berkeley Lab's Molecular Foundry. "By tuning its thermal conductivity, the material can efficiently and automatically dissipate heat in the hot summer because it will have high thermal conductivity, but prevent heat loss in the cold winter because of its low thermal conductivity at lower temperatures."



New beam pattern yields more precise radar, ultrasound imaging
ROCHESTER, N.Y. - University of Rochester researchers have developed a novel beam pattern that promises to lend unprecedented sharpness to ultrasound and radar images.

The beam's mathematical pattern yields wavelengths that momentarily collapse in on themselves, briefly forming a precise and powerful beam of sound or light waves.

"All the energy fits together in time and space so it comes together -- BAM! -- like a crescendo," Kevin Parker, a professor of engineering at Rochester, said in a news release. "It can be done with an optical light wave, with ultrasound, radar, sonar -- it will work for all of them."

Researchers say the pattern could also be used to make precise incision and holes in nanoscale structures or etch fine patterns into the surface of materials.

Unlike other beam patterns, which often dissipate some energy laterally in the form of "side lobes," the new beam patterns is extremely efficient.

"Side lobes are the enemy," said Miguel Alonso, a professor of optics. "You want to direct all of your ultrasound wave to the one thing you want to image, so then, whatever is reflected back will tell you about that one thing. If you're also getting a diffusion of waves elsewhere, it blurs the image."

The work of Parker and Alonso -- detailed in the journal Optics Express -- continues Rochester's tradition of breakthrough beam discoveries. In 1986, a time of Rochester physicists discovered a now widely used pattern known as the Bessel beam.

"It had been decades since anyone formulated a new type of beam," Parker said. "Then, as soon as the Bessel beam was announced, people were thinking there may be other new beams out there. The race was on. Finding a new beam pattern is a like finding a new element. It doesn't happen very often."

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