Physics Tip Sheet #3 - March 6, 2002

Contact: David Harris
harris@aps.org
301-209-3238
American Physical Society

1) The origins of friction
arXiv preprint server

Scientists have long-debated the microscopic origin of friction between macroscopic surfaces. A new experimental analysis finds that two metallic surfaces placed together spontaneously deform to create an Angstrom-sized bond. This bond then grows in size over about one minute to nanometer levels. These bonds account for the slip-stick friction observed as two metal surfaces slide over each other. The measurements of this microscopic phenomenon were performed with a fiber-optic cantilever surface probe microscope that is sensitive to sub-nanoscale motions.

Preprint: http://www.arxiv.org/abs/cond-mat/0203075

2) Ping-pong polymers
Physical Review E (Print issue: March 2002)

In a low-tech experiment, researchers have simulated the behavior of complex molecules in solvents by putting a chain of plastic spheres in a bath of randomly moving balls that are often used as toys for pets. The random motion of the balls simulates the thermal jiggling of molecules known as Brownian motion. With a video camera and simple image recognition, the folding and unfolding of the molecule and other molecular processes can be simulated and analyzed. The results are applicable to many areas of polymer and statistical physics.

Journal article: http://link.aps.org/abstract/PRE/v65/e031306

3) Turning the superconductivity mechanism inside out – bosons into fermions
arXiv preprint server

Superconductors have their characteristic properties because of Cooper pairing – a phenomenon in which pairs of interacting fermions (spin-1/2 particles such as electrons) join together in pairs and act as non-interacting bosons (spin-1 particles). At the most simplistic level, the two spin-1/2 particles add together to give spin-1. Therefore it is surprising that the reverse procedure can happen – collections of interacting bosons can act just like non-interacting fermions. A new analysis shows how this might be experimentally achieved using a cold rapidly rotating gas of bosons (much like a Bose-Einstein condensate). By combining bosons in the right way (a process dubbed fermionization), effective particles of any fractional spin can be created.

Preprint: http://www.arxiv.org/abs/cond-mat/0203061

4) Matter-wave interferometer for large molecules
Physics News Update/Physical Review Letters
(Print issue: March 11, 2002)

Large fullerene molecules (C_70, consisting of 70 carbon atoms each) have been made to show wave interference in good agreement with quantum predictions. The fullerenes are passed through three gratings made of finely spaced gold wires and found to leave a pattern of peaks and troughs unlike the “flat” pattern for classical particles.

Physics News Update: http://www.aip.org/enews/physnews/2002/split/579-1.html
Journal article: http://link.aps.org/abstract/PRL/v88/e100404

5) Stability of sand dune fields
arXiv preprint server

Individual sand dunes are known to move downwind at a velocity dependent on height. So why don’t dunes of different heights bump into each other? A new model of sand dune dynamics accounts for the interaction between dunes in terms of inter-dune sand flow. The model examines the case of barchan (crescent-shaped) dunes and predicts the stability of dune fields giving results in agreement with actual dune fields in nature.

Preprint: http://www.arxiv.org/abs/cond-mat/0202528
Other sand dune preprints: http://www.arxiv.org/abs/cond-mat/0203040, http://www.arxiv.org/abs/cond-mat/0203081

6) Superconductors show their stripes
Physical Review Focus/Physical Review Letters
(Print issue: March 4, 2002)

A controversial theory of superconductivity has received a boost by the observation of stripes within the charge structure of the common yttrium barium copper oxide (YBCO) superconductors. The theory says that stripes of charge “protect” electric current running between them from disruption, thereby assisting the transition from low electrical resistance to true superconductivity. Previous studies in lanthanum strontium copper oxide provided some evidence for this stripe mechanism but required the addition of impurities to hold the stripes still. Another upcoming paper in PRL provides more observations of stripes in YBCO and a study of bismuth strontium calcium cuprate also shows stripes.

Physical Review Focus: http://focus.aps.org/v9/st12.html
Journal article: http://link.aps.org/abstract/PRL/v88/e097004
Second YBCO study preprint: http://www.arxiv.org/abs/cond-mat/0108053
BiSrCaCuO preprint: http://www.arxiv.org/abs/cond-mat/0201546

7) One-way heat flow Physical Review Focus/Physical Review Letters
(Print issue: March 4, 2002)

A proposal for new materials may restrict heat to flowing in one direction, analogously with electronic diodes. The authors suggest that these types of materials could be built with DNA strands or could be built with nanotechnology. Thermal diodes could reroute excess heat in a microchip or thermal transistors might run a “lab-on-a-chip” where temperature controls biochemical reactions.

Physical Review Focus: http://focus.aps.org/v9/st11.html
Journal article: http://link.aps.org/abstract/PRL/v88/e094302

Papers from the Physical Review series of journals are available pre-publication to journalists on request.

For media assistance with these or other physics stories, contact:

David Harris
Head of Media Relations
American Physical Society
Ph: +1 301 209 3238
Fax: +1 301 209 3264
Email: harris@aps.org