March 12, 2014
Diamonds And Superconductors
They say that diamonds are forever. Well, to be fair, the marketing of diamond jewelry says that. Personally, I found the reference Family Guy made to those commercials more to-the-point. Nothing lasts forever, another popular saying, goes directly counter to the “diamonds are forever” line we have been fed for years now, so I think it is time that diamonds got a new catchphrase. Diamonds, they shine like the stars? No, too campy. Diamonds, they are a thing? Spot on, but it would never sell. Diamonds, woman’s best friend? No, way too sexist, and I believe I have heard that somewhere already. Oh, I got it. Diamonds, a superconductor’s best friend. Perfect.
Diamonds, specifically colorful diamonds – those that have flaws in their carbon structure which allow some of the carbon atoms to be replaced by another element, such as boron, that emits/absorbs various colors of light – are some of the most sensitive detectors of electromagnetic fields in the world. They allow physicists to study the minuscule magnetic fields found in metals, exotic materials, and even in human tissue. Recently, it has been discovered that these diamond sensors can even measure the small magnetic fields in high-temperature superconductors, exotic mixes of materials like yttrium or bismuth that, when they are cooled to around negative 280 degrees Fahrenheit (that is only 180 degrees warmer than absolute zero, which is -459.67 degrees Fahrenheit) lose all resistance to electricity. This discovery was made my physicist Dmitry Budker of the University of California, Berkeley, and his colleagues at Ben-Gurion University of the Negev in Israel, and UCLA. For their experiment, they bombarded an artificial diamond with nitrogen atoms in order to knock the carbon atoms out of it, leaving a combination of holes and nitrogen atoms in the diamond. Then they heated it, which forced the vacancies (holes) to move and pair up with the nitrogen atoms, which resulted in diamonds with nitrogen-vacancy centers. For the negatively charged vacancy centers, the amount of light that they re-emit when hit with light becomes highly sensitive to magnetic fields, which is what allows them to be used as sensors that can then be read out by laser spectroscopy. It was also noted by Ron Folman of Ben-Gurion University of the Negev that the color centers of the diamonds have a unique property to exhibit quantum behavior, one that is lacking in most other solids at room temperature, which is in part why these new sensors have such great potential.
Using their new diamond sensor to measure the properties of a thin layer of yttrium barium copper oxide (YBCO), which is one of the two most popular types of high-temperature superconductor. The team integrated the diamond senor with the superconductor on a chip and used it to detect the change from normal conductivity to superconductivity. The sensor was also able to detect tiny magnetic vortices, which show up as the material reaches superconductivity and are believed to be a key to understanding just how these materials become superconducting at high temperatures.
Diamonds, a superconductors best friend. I like the sound of that. Of course, given what they have helped physicists learn, maybe they should be called “a physicists best friend” instead.
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