In the Hollywood movie Avatar, humans attempt to exploit the mineral wealth of Pandora in the face of stiff resistance from the local humanoid tribe Na’vi. The invading humans were lured by the abundance of the wonder mineral unobtanium, a superconductor at room temperature. In Avatar, as in other science fiction works, imagination takes precedence over reality as superconductors at ambient room temperatures are not known yet. Scientists have been searching for real minerals similar to the fictitious unobtanium for over a century without much success. Such superconductors will revolutionise many facets of our lives—from power distribution and transportation to medical diagnosis. Unsurprisingly, when two scientists at Bengaluru’s Indian Institute of Science announced last year that they had achieved superconductivity at room temperature, the news was an instant sensation. After some false starts and debates about its validity, it was reportedly confirmed again recently after extended experimentation.
The drama surrounding this news from Bengaluru is not unusual. The history of the search for superconductors at room temperature is replete with serendipity, false alarms and Nobel prizes. Long before superconductors, there were standard conductors or wires that carry electricity thanks to Michael Faraday’s work. In 1831, Faraday demonstrated a method to generate electricity by moving a magnet through coils of copper wire. The apocryphal story goes that the then British Chancellor of the Exchequer William Gladstone witnessed the demonstration and asked him what the practical value of his invention was. To this, Faraday replied, “One day, Sir, you might tax it.” To this day, not only is electricity taxed, but the basic principles of power generation have remained unchanged.
By the 1880s, when the first commercial power generation started in the US, the basic physics of electricity and magnetism was well understood. When current flows through metallic conductors, the atoms in the conductor tend to resist the current flow. Resistance was thought to be unavoidable then. At the turn of the 20th century, a veritable race was underway to realise extremely low temperatures in the laboratory. In 1908, the Dutch physicist Kamerlingh Onnes turned Helium gas into its liquid form and attained a temperature of -271.6°C. This is far colder than any place on earth and only slightly above the lowest possible temperature called absolute zero. When he cooled mercury down to such low temperatures, quite unexpectedly, mercury lost all resistance to current flow. A terse entry in his lab notebook on 11 April 1911, “kwik nagenoeg nul” (Mercury nearly zero), heralded the superconductivity era and Onnes was bestowed the Physics Nobel in 1913.
Two decades later, two German scientists discovered that magnetic fields are expelled from the material when superconductivity sets in. The combination of zero resistance and no magnetic field is a spectacular and counterintuitive physical effect. The biggest drawback was superconductivity could be maintained only at impossibly low temperatures using expensive liquid Helium. For practical purposes, superconductivity must work at room temperatures like the fictional material unobtainium. For more than a century now, scientists have been chasing this Holy Grail—a material that would superconduct at room temperature and pressure. The Bengaluru-based scientists claim to have achieved precisely this at 13°C using a gold-silver nanostructure mixture.
For a scientist, as Sherlock Holmes would say, “there is a mystery about this which stimulates the imagination”. The mechanism of superconductivity, shrouded in mystery, was partially unravelled in the 1950s by John Bardeen, Leon Cooper and John Schrieffer (BCS) and fetched them the Nobel in 1972. They showed how quantum effects at sufficiently low temperatures created ‘expressways’ within materials through which electrons travelled without encountering any resistance. In the next few decades, imagination, science and serendipity led to superconductors at higher temperatures that did not fit the BCS template. Significant advances using ceramic materials during 1986-87 pushed the superconducting temperatures to as high as -183°C, well within the regime of the cheaper liquid Nitrogen. The 1987 Physics Nobel honoured this pioneering work.
Through all these developments, room-temperature superconductivity still remained elusive though its practical consequences were well appreciated. Power distribution grids would be far more efficient than they are and we can achieve nearly zero transmission losses. MRI scanners routinely used in hospitals for imaging could become better and cheaper. Perhaps the biggest eye-popping change will be transportation powered by superconducting magnets. In 2015, Japan tested its maglev train that levitates a few cm above the track (remember Avatar’s floating mountains) while moving forward at speeds of 600 km/hour. The first commercial service between Tokyo and Nagoya is expected to start in 2027. A room-temperature superconductor will make maglev tech economically attractive and a preferred transportation mode of the future.
If the superconductivity observed by the Bengaluru group is sustained by due scientific process of peer review and independent trials in other laboratories, it might rank alongside the significant discoveries made in India. And there will be technological spin-offs. Sadly, the stunning visuals of floating mountains seen in Avatar might not look magical. Science fiction will not be fiction anymore.
M S Santhanam
Physicist and a professor at the Indian Institute of Science Education and Research, Pune
Email: santh@iiserpune.ac.in