Mercury superconductivity understood, finally
THEORISTS have finally explained the superconductivity of mercury, the first superconductor ever discovered. In 1911, three years after he invented the method to liquefy helium to 4 degrees kelvin (about −269 °C), the Dutch physicist Heike Kamerlingh Onnes succeeded in cooling mercury down to 4.2 K using liquid helium. He passed current through mercury wire and found that its electrical resistance vanished at 4.2 K. He wrote: “The experiment left no doubt about the disappearance of the resistance of mercury. Mercury has passed into a new state, which because of its extraordinary electrical properties may be called the superconductive state.”
Although mercury was later found to be a “conventional” superconductor, no microscopic theory managed to fully explain the metal’s behaviour or predict the temperature at which it becomes a superconductor (critical temperature). To tackle the problem of this incomplete understanding, Gianni Profeta of the University of L’aquila, Italy, and colleagues scrutinised all physical properties relevant to conventional superconductivity. Their first-principles calculations accurately predicted mercury’s critical temperature. The work was published in the latest issue of Physical Review B. Their prediction of critical temperature was only 2.5 per cent lower than the experimental value. The new understanding of the oldest superconductor may offer valuable lessons for superconductivity research, said Profeta.
By identifying theoretical caveats, the work has provided insights relevant to searches for room-temperature superconductors. A promising material-by-design approach in the search for superconductivity in ambient conditions involves “high-throughput” computations that screen millions of theoretical material combinations. “If we don’t include subtle effects similar to those relevant for mercury, these computations may overlook many interesting materials or err in their critical temperature predictions by hundreds of kelvins,” Profeta said.