Physics Tip Sheet #83, July 30, 2008

• New colossal carbon tubes created
• Flipping spins at the speed limit

Colossal Carbon Tubes leave Kevlar and Nanotubes in the Dust

H. Peng, D. Chen, J.-Y. Huang, S. B. Chikkannanavar, J. Hänisch, M. Jain, D. E. Peterson, S. K. Doorn, Y. Lu, Y. T. Zhu, and Q. X. Jia
Physical Review Letters (forthcoming)

A collaboration of Chinese and American physicists has discovered a way to make a new carbon structure that could lead to fabrics 30 times stronger than Kevlar and 224 times stronger than cotton. The group dubbed the structures colossal carbon tubes because they're thousands of times larger than carbon nanotubes. At 40-100 millionths of a meter across and centimeters long, they're comparable in size to typical cotton fibers.

The structures consist of nested inner and outer tubes separated by hollow channels, making the tubes both light and strong. While they are nowhere near as strong as carbon nanotubes, the colossal tubes are much more ductile than the nanoscopic variety, making them more suited for spinning into threads and weaving into fabrics. The colossal tubes conduct electricity and show some of the properties of semiconductors, which means that they could lead to novel microelectronic components as well as super strong cloth.

The details regarding how the intricate structures form is still hazy, but the researchers propose that colossal carbon tubes could be incorporated into improved body armor, stronger carbon fiber composites (which are often shaped into parts for high-performance and lightweight vehicles), or components in microelectronics and tiny machines. - JR

Spin Flips Hit the Speed Limit

S. Serrano-Guisan, K. Rott, G. Reiss, J. Langer, B. Ocker, and H.W. Schumacher
Physical Review Letters (forthcoming)

A team of physicists at Physikalisch-Technische Bundesanstalt in Germany has managed to flip a nanoscopic magnet as fast as the fundamental speed limit allows. Their experiment consisted of two stacked layers of tiny magnets separated by a thin barrier to form what is called a magnetic tunnel junction. Such magnetic tunneling junctions are promising candidates for future magnetic memory chips.

The researchers allowed electrons aligned in a special way to flow between the layers, developing a spin torque, or twisting force that is transferred from one layer of nanomagnet onto the other. This torque pumps enough energy to the nanomagnet to make it move faster and faster until it changes direction. Several measurements showed that the researchers were able to switch the direction of magnetization as fast as physically possible.

Their spin torque record is important for the next generation of low current, ultra fast magnetic memory chips and sensors. This new generation of electronics encodes information in an electronic spin, rather than in an electronic charge. The spin torque switching effect is a powerful new approach to controlling electronic spins. - NR

50 Years of PRL

Martin Blume

Physical Review Letters turns 50 this year. Martin Blume is celebrating the green journal's birthday by summarizing the most intriguing papers to appear in PRL each year since 1958. To see past editions of Marty's Milestone PRL project, visit http://prl.aps.org/50years/milestones

This week, Marty is taking a look at a milestone paper from 1982 that led to the 1998 Nobel Prize in Physics.

Two-Dimensional Magnetotransport in the Extreme Quantum Limit
D. C. Tsui, H. L. Stormer, and A. C. Gossard
Phys. Rev. Lett. 48, 1559 (1982)

Following on the discovery of the integer Quantized Hall Effect by von Klitzing and coworkers, Tsui, Stormer, and Gossard undertook studies of a two-dimensional electron fluid at higher magnetic fields and lower temperatures than had previously been done. In this Letter they presented surprising results showing a plateau of the Hall effect at 1/3 the von Klitzing conductance value, (1/3)(e2/h). Several explanations for the results were discussed in the Letter, but the authors finally concluded "At the present there is no satisfactory explanation for all of our observations". Many possible explanations were put forward by others in a flurry of papers, but the conclusive explanation was given by Laughlin in 1983 (selected as a Milestone for that year). He showed that a new state of matter with many-particle interactions accounted for the experimental results.

The 1998 Nobel Prize in Physics was awarded to R. B. Laughlin, Horst Stormer, and Daniel Tsui "for their discovery of a new form of quantum fluid with fractionally charged excitations". See Physical Review Focus 2, story 18 (http://focus.aps.org/story/v2/st18) for a readable description of this work.

Nadia Ramlagan and James Riordon contributed to this Tip Sheet.

About APS

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