Inside of the diamond cell: In the middle is the coil system around the diamond anvil, which picks up the shielding signal from the superconducting sample. Credit: James Schilling, Washington Univ.
A duo from Washington University in St. Louis reports they have for the first time found a way to tap superconductivity properties of europium.
In work funded by the materials research division of NSF, WUSTL professor James Schilling and then-doctoral student Mathiewos Debessai found that europium becomes superconducting at 1.8 K (-456°F) and 80 GPa (790,000 atmospheres) of pressure, making it the 53rd known elemental superconductor and the 23rd at high pressure. Schilling and Debessai used a diamond anvil and coil system to conduct their measurements.
“It has been seven years since someone discovered a new elemental superconductor,” Schilling said. “It gets harder and harder because there are fewer elements left in the periodic table.”
Europium isn’t an obvious superconductor. As a rare earth element, its natural magnetic properties actually run counter to superconductivity. “Superconductivity and magnetism hate each other. To get superconductivity, you have to kill the magnetism,” Schilling explained.
However, armed with the insight that europium should be the easiest of the rare earths to lose magnetic properties under high compression, the researchers. “When europium atoms condense to form a solid, only two electrons per atom are released and europium remains magnetic. Applying sufficient pressure squeezes a third electron out and europium metal becomes trivalent. Trivalent europium is nonmagnetic, thus opening the possibility for it to become superconducting under the right conditions,” Schilling said.
“Theoretically, the elemental solids are relatively easy to understand because they only contain one kind of atom,” Schilling said. “By applying pressure, however, we can bring the elemental solids into new regimes, where theory has difficulty understanding things. When we understand the element’s behavior in these new regimes, we might be able to duplicate it by combining the elements into different compounds that superconduct at higher temperatures.”
Schilling and Debessai’s findings are published in a recent issue of Physical Review Letters in an article titled “Pressure-induced Superconducting State of Europium Metal at Low Temperatures.” Schilling is also presenting their research at the International Conference on High Pressure Science and Technology in July, 2009, in Tokyo, Japan.
