IF Josephson junction brings to mind an intersection of two small back roads, it's time to change gears and think science. This term, along with quasi-particle and Cooper pair, is part of the large area of superconductors.|
Simon Labov and his colleagues in Lawrence Livermore's Physics and Space Technology Directorate say these concepts and discoveries show great promise for applications in areas such as wireless communication, energy storage, and medical diagnostics. Labov and his fellow researchers are using superconductors to create a new generation of supersensitive detectors for nondestructive evaluation and astrophysics.
When ordinary metal conducts electricity, the electrons carrying the current collide with imperfections in the metal, thereby creating resistance. But when a superconducting material is cooled to its critical temperature, electrons pair off into Cooper pairs, named for Leon Cooper, one of the scientists who won a 1972 Nobel Prize in physics for explaining the now widely accepted theory. Any movement of one electron is matched by equal and opposite movement of the other. As a result, they don't hit the imperfections, no electrical resistance is generated, and electrons flow freely, without the addition of more energy.
But to put these theories to practical use in detectors requires a Josephson junction. Named for Brian Josephson, who described the theory when he was a graduate student at Cambridge University in 1962, a Josephson junction is two pieces of superconducting material linked by a weak insulating barrier. When an x ray hits a Josephson junction, the Cooper pairs break up, and quasi-particles are created. These quasi-particles, which are electronlike or holelike excitations in the superconductor, can tunnel through the weak insulating barrier of the Josephson junction, producing a pulse of electrical current. By measuring the number of Cooper pairs that are broken, scientists can determine the energy of the x ray up to ten times better than with conventional technology and can identify the material that emitted the x ray. These superconducting-tunnel-junction (STJ) detectors also work with optical, ultraviolet gamma-ray photons and large biomolecules. Labov and his team are working to use this new technology in applications for analyzing all of these particles.
Measuring Large, Slow Molecules
High Resolution for Soft X Rays
Detecting Impurities as Semiconductors Shrink|
As semiconductor devices continue to shrink, the industry needs to detect and identify small amounts of contamination on the devices. Microanalysis systems with conventional energy-dispersive spectrometers "excite" contamination on chips with fairly high (10-kiloelectron-volt) energy, which results in the surrounding material also being excited. When the surrounding material is excited, a flood of unwanted signals or noise is created, making it impossible to detect the contamination. But STJ detectors can operate with excitation energies of less than 2 kiloelectron volts, which produce signals from the contamination only, allowing the imperfections to be detected.
Helping to Enforce Nonproliferation
Looking toward the Future
Key Words: atomic spectroscopy, Cooper pairs, detectors, Josephson junction, mass spectrometry, quasi-particles.
For further information contact Simon Labov (925) 423-3818 (firstname.lastname@example.org).