A research team at the Tata Institute of Fundamental Research in Mumbai have discovered a new property of the chemical element Bismuth that could change the entire study of superconductive materials, which are those substances that can conduct electricity without resistance.
In a peer-reviewed paper published in Science magazine’s December issue, the researchers at TIFR demonstrated properties of superconductivity in a high-quality single crystal of Bismuth, a semi-metal that is the 83rd element in the periodic table. Scientists once thought superconductivity in bulk for Bismuth was very unlikely.
“We knew that if you could establish superconductivity in Bismuth, it will lead to a new theory of superconductivity,” said S Ramakrishnan, a professor who led the research. “We wanted to show that if it is a superconductor, it will be a completely new one.”
Bismuth is a very unusual element in the periodic table and it has properties very different from other superconducting metals, he explained. In other metals, there is one mobile electron per atom and this conducts electricity. In Bismuth, one mobile electron is shared by 1,00,000 atoms. The researchers at TIFR found, at ultra low temperatures, the element can become a superconductor.
Scientists had earlier considered the possibility that Bismuth might be a superconductor, but they did not examine its properties below a certain temperature and so gave up the idea. In 2011, TIFR installed a copper nuclear refrigeration unit that can produce low to ultra-low temperatures. This unit was used to produce the results by January 2016. Only 20 such units exist in the world.
Ordinary conductors of electricity, like copper, produce resistance – this means an electric current cannot run through them indefinitely. Superconductors, however, can conduct currents indefinitely because they have no resistance. Superconductors are used in machines as diverse as MRIs in hospitals to particle accelerators such as the Large Hadron Collider.
The Bardeen-Cooper-Schrieffer theory which explained how superconductivity works in 1957 explains the mechanism for all other metals. A theory explaining how it works in Bismuth is yet to be formulated.
“We are eagerly waiting for the theory,” Ramakrishnan said. “If that comes, we can cook up other elements that come up with superconductivity at more comfortable temperatures. We have to work together with theorists to really understand what is happening.”