The proximity of the high-Tc squid to samples makes it possible to use the microscope on living organisms as well as other specimens that cannot be chilled to sub-freezing temperatures. This could, among other benefits, pay big dividends for bioremediation projects which propose using bacteria to convert hazardous waste into harmless byproducts.

Lee and Chemla have begun training the microscope on a strain of bacteria that is endowed with special magnetic properties. Like all bacteria, these creatures swim with the help of whiplike tails, called flagella, which means they should be able to serve as a model organism for the study of bacterial migration patterns in general. What makes this strain unique, however, is that each bacterium carries about twenty magnetite particles along the centerline of its body. This unique evolutionary feature enables the bacteria to swim along the direction of the earth's magnetic field lines which helps them migrate towards food sources in lake bottoms.

"These magnetotactic bacteria are like magnets," says Chemla, "and we are able to see them and record in detail the dynamics of their activity in solution."

With the high-Tc squid microscope, Lee and Chemla can detect changes in the magnetic fields of the bacteria produced by extremely subtle motions. They can measure not only the frequencies of bacterium movements but also the relative amplitudes.

"As its flagellum propels a bacterium forward, imbalances in the tail cause the bacterium to wobble or gyrate, generating a fluctuating magnetic field at about 70 Hertz," explains Chemla. "Furthermore, because the flagellum is attached to the bacterium away from the centerline, imbalances in drag forces cause the bacterium to precess at about 25 Hertz."

The bacteria being used in this study were grown by Bob Buchanan and Mike Adamkiewicz of UC Berkeley's Department of Plant and Microbial Biology.

In the long run, Lee and Chemla would like to devise a means of magnetically tagging all types of bacteria. Since a similar tagging has been done with antibodies, Chemla says the idea is not beyond reach. If successful, it would provide environmental researchers with a tool for evaluating and comparing different microorganisms so that the best could be selected for each specific bioremediation project.

"To develop better methods of bioremediation, we need to improve our understanding of how these bacteria migrate through a soil or sand sample towards regions of higher waste concentration," says Chemla. "Since these media are opaque, optical techniques are inadequate for monitoring this migration."

The high-Tc squid microscope also offers intriguing promise as a tool for the early evaluation of the structural integrity of steel and other construction materials. For example, microcracks in steel can be harbingers of catastrophic failure, but by the time these microcracks appear, it may be too late -- the material's failure may be imminent. Other groups have already used squids to observe changes in the magnetic behavior of steel after it has been subjected to mechanical stress in an effort to forecast possible trouble.

In close collaboration with the high-performance metals research group of J. William Morris, at Berkeley Lab's Center for Advanced Materials, Clarke's group is building a modified version of their high-Tc squid microscope which would be capable of carrying out magnetic studies at the time the steel undergoes mechanical stress. These magnetic measurements would then be tied into structural information gathered with the powerful transmission electron microscopes at Berkeley Lab's National Center for Electron Micro- scopy (NCEM) in a collaboration with MSD scientist Kannan Krishnan.

Says Clarke group member Tim Shaw, "Our aim is to improve on previous studies by recording two-dimensional magnetic images of steel with a spatial resolution of approximately 100 microns, and to correlate changes in the magnetic behavior, caused by heat treatment and stress, with structural changes."

In addition to shedding light on the underlying physics of magnetic behavior, the collaboration hopes to produce a typology of magnetic signatures in steel that could predict likely structural failure long before the appearance of any microcracks.

Despite all the advances being made with the high-Tc squids by Clarke and his group, as well as by other research groups around the world, the need for low-Tc squids will continue. Why? Because low-Tc squids are more sensitive than high-Tc squids and always will be. Consequently, Clarke and his group continue to work toward developing new and improved breeds. One of the most intriguing applications of these new low-Tc devices is to detect a mysterious species of subatomic particle that may or may not exist. This hypothetical particle has been named the "axion" and it is one of the candidates for explaining the nature of dark matter.

Approximately 90-percent of the matter that comprises the known universe does not radiate any electromagnetic radiation, hence it has been dubbed "dark." Though invisible to us, dark matter makes its massive gravitational presence known through the motions of the galaxies. Determining its nature poses one of the great scientific challenges with implications for both the birth and the ultimate fate of the universe.

Axions are thought to decay into photons when they enter an intense magnetic field. Since 1995, there has been an experiment in progress at the Lawrence Livermore National Laboratory (LLNL), to search for axion decay products within a strong magnetic field. However, for a definitive experiment, the apparatus currently in use needs a much better amplifier. Clarke and Marc-Olivier Andre have begun a collaboration with a team led by LLNL's Karl van Bibber and Les Rosenberg of MIT to build a device which will incorporate as its signal amplifier a special low-Tc squid designed to operate as a 0.5 to 1.0 gigahertz radio-frequency amplifier.

"No one has yet produced a squid amplifier that operates successfully at such high frequencies," says Clarke. Equipped with this new detector, the experiment at LLNL could clarify the existence of axions and either give cosmologists a leg up on their dark matter research, or send them back to the drawing board.

Other major participants on this low-Tc squid amplifier project are Edward Daw of MIT, and Pierre Sibivie of the University of Florida.

Clarke and his research group are heavily involved in other squid-based projects as well. These projects are aimed at answering fundamental physics questions about superconductivity, both the low and high temperature varieties, and at better understanding the chemical environments of atoms and molecules. This latter work involves the coupling of low-Tc squids to nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) technologies. It is being done by Clarke group member Dinh Ton in collaboration with Matt Augustine, a member of the research group of Alex Pines (see Research Review, Spring 1997).

NMR and NQR are used by scientists to study the structural, dynamic, and spatial relationships of atoms in gases, liquids, and solids. The use of a low-Tc squid amplifier with either technique enables researchers to study atoms at much lower frequencies than ever before (meaning with greater sensitivity), especially in polycrystalline and amorphous materials.

"Recently, they (Ton and Augustine) made a two-dimensional image of frozen xenon at 61 Hertz, the lowest frequency at which a magnetic resonance image has ever been obtained," says Clarke.

Often scientists who make a major discovery or landmark achievement early in their career move on to other fields or other areas of research away from their initial success. After his success at Cambridge, John Clarke left to come to Berkeley. But he did not leave the study of squids. He has stayed the course through three decades, and science continues to reap the benefits.