Latest Research in BEC, MgB2 Among March Meeting Highlights

The biggest physics meeting of the year, the APS March Meeting, was held March 18-22, 2002 in Indiana at the Indianapolis Convention Center. An estimated 5000 talks were delivered.

The March Meeting is traditionally a showcase for important fundamental physics as well as the kind of practical research that shows up - five, ten, or even 20 years later - in the productive labor-saving devices we take for granted.

This year's conference was no exception, as speakers presented the latest research results in Bose-Einstein condensates (page 1), physics-based tools for medicine (page 6), and the future of information technology. In addition to the technical sessions-several highlights of which are described below-there were also a series of workshops on Sunday, including one on career planning and development (page 3) and successful strategies for women physicists (page 1).

Hopes for a Hole-Doped Metal Superconductor.

The Whip Vigorously twirling the plastic tube is James Watson, of Ball State University, who with his wife Nancy led a workshop on the physics of toys at the High School Physics Teachers’ Day held in Indianapolis as part of the March meeting. Each participant in this workshop received one of these tubes and about thirty other inexpensive toys that students can use for informal physics learning.

Last year a new record was set for a superconductor transition temperature, 40 K, for an all-metal compound. Much more is known now about these MgB₂ materials.

There is now hope that a related compound, LiBC, might operate at temperatures at high as 100 K, as much as twice as high as for MgB₂.

At the APS meeting, Warren Pickett of UC Davis pointed out that the interactions that are the essence of superconductivity, the pairing of electrons brought about by the interactions between electrons and concerted flexings (phonons) in the material lattice, are potentially twice as strong in LiBC than in MgB₂ especially if holes (the momentary vacancies left behind by departed electrons) can be injected into the sample by a "field-effect" process.

This is a common procedure in transistors, where a gate electrode forces holes into a channel between the other two electrodes, thus enhancing the conductivity in that region, inducing a metallic state and producing superconductivity.

A field-effect setup helped to boost the superconducting transition temperature in a crystal of carbon-60 molecules up to 117 K last year.

Terahertz Imaging: A New Inspection Technology.

Physicists are still discovering useful regions in the rainbow spectrum of electromagnetic radiation.

One such region is the realm of terahertz radiation, electromagnetic radiation corresponding to far-infrared light. Terahertz radiation is transparent to many packaging materials, making it attractive for product inspection, quality control, and detection of explosives, including plastic ones. It's very sensitive to water, making it useful for environmental monitoring. It also can produce images with details smaller than a millimeter.

Daniel Mittleman of Rice University kicked off a Wednesday focus session on terahertz technology, followed by Irfan Siddiqi of Yale, who discussed experimental results on a device for "terahertz astronomy," which would make astronomical observations in the far-infrared region, where optical and radio astronomy techniques often falter. THz astronomy is especially promising for watching the birth of stars in molecular clouds .

Helium in Aerogel

Douglas Osheroff of Stanford garnered a Nobel Prize for observing how helium-3 becomes superfluid at a temperature of .0027 K. Since then scientists have sought to understand the mysteries of liquid He-3, which exists in not one but three superfluid phases, which have different magnetic and mechanical properties.

One approach is to insert liquid helium into aerogel, that airy material hardly denser than air. The microscopic filaments of aerogel are supposed to act like one-dimensional impurities (rather than the usual point defects), and this acts to disrupt the process by which He-3 atoms pair up in the act of becoming superfluid. On Thursday, Osheroff reported the first observation of a transition between the A and B phases of liquid helium-3 in aerogel.

Slime Propulsion

Many types of bacteria get around by gliding across surfaces. Hair-like structures called pili propel the microorganisms when they travel in groups during herd-like migrations known in the field as social or s-type motility. The mechanism that bacteria use when they venture out alone (adventurous, or A-type, motility), however, has long been a mystery.

Charles Wolgemuth (University of California at Berkeley) and coworkers think they have identified the vehicle that facilitates a bacterial walkabout-slime. Wolgemuth presented a slime propulsion model and experimental evidence for the unsavory conveyance in a Tuesday session.

Vive La Différence

Sex, it seems, has both advantages and disadvantages.Ayse Erzan of the Istanbul Technical University has modeled some of the issues facing single-celled organisms that reproduce either through sexual pairing or through asexual division, and found clues that indicate why sex gives many organisms an evolutionary upper hand.

Ezran's talk was one of a dozen in a Thursday session dedicated to the dynamics of evolution. Later in the session, Graeme Ackland (University of Edinburgh) and Michael Clark (Institute of Terrestrial Ecology, Scotland) painted a picture of a world covered in flowers as they discuss the thermodynamics of an evolving system as it applies to Lovelock's "daisyworld"- a hypothetical two-dimensional world consisting of an infinite plain of daisies.

The mechanisms that help clawed frogs detect their prey, optimal wiring in the cortex, and the molecular evolution of a genetic switch were just a few of the other subjects competing for attention in the session.

The Computer Never Forgets

When you turn off an ordinary computer, its RAM (random access memory) is lost. On Thursday, Jimmy Zhu of Carnegie Mellon University described a new memory technology, called magnetoresistive random access memory (MRAM), which is nonvolatile: its memory is retained even after the computer is shut down. Whereas traditional RAM uses electric charge to store 0s and 1s of data, MRAM exploits the magnetic properties of electrons in the device. MRAM stores data by taking advantage of the fact that electrons act like tiny bar magnets in the presence of an magnetic field: 0 can represent the bar magnet when it is aligned with a field and 1 when it is opposite the direction of the field.

MRAMs have many attractive features, yet a major drawback has been their relatively large power consumption: in traditional MRAM designs, less than 1% of the power is used to write the 0s and 1s of data, while over 99% of the power is wasted in delivering the electric current for writing the data.

Zhu's novel memory device design consumes significantly less power and is much more stable than previous designs. Such a design may bode well for miniaturizing this technology to the nanometer dimensions necessary for many commercial applications.

Phillip F. Schewe, Benjamin P. Stein and James Riordon of AIP and David Harris of APS contributed to the coverage of March Meeting sessions in this issue.