21-Jun-2019: IISc researchers report superconductivity at room temperature.

About a year ago, two scientists from Indian Institute of Science (IISc)-Bangalore had observed superconductivity at room temperature, in a new composite material made of gold and silver. The claim created huge excitement.

Superconductivity is a phenomenon that, so far, has been possible only at extremely low temperatures, in the range of 100°C below zero. The search for a material that exhibits superconductivity at room temperature, or at least manageable low temperatures, has been going on for decades, without success. If the claimed discovery were confirmed, it could be one of the biggest breakthroughs in physics in this century so far.

The claim of Anshu Pandey and his PhD student Dev Kumar Thapa, the two researchers, was met largely with skepticism, criticism, even ridicule. Questions, many of them meaningful, were raised about the authenticity of data produced, the experimental procedures followed, and whether the interpretations they were making from the data were correct.

Amid increasing criticism, IISc asked some senior subject specialists to collaborate with the two researchers and reexamine the results. That group, which included the original two researchers, last month reported the results of fresh experiments on new samples of the same material, and reiterated not just the original findings, but much more. The group has also sent a paper for publication in an international journal. Their paper, as of now, is under “technical review”.

Superconductivity is a state in which a material shows absolutely zero electrical resistance. While resistance is a property that restricts the flow of electricity, superconductivity allows unhindered flow. Electricity is essentially the movement of free electrons in a conducting material like copper. While the movement of electrons is in one particular direction, it is random and haphazard. They frequently collide with one another, and with other particles in the material, thus offering resistance to the flow of current. The picture is similar to one of messy traffic in a congested urban area. In the process, a lot of electrical energy is lost as heat. Resistance is a measurable quantity, which varies with the material.

In a superconducting state, however, the material offers no resistance at all. All the electrons align themselves in a particular direction, and move without any obstruction in a “coherent” manner. It is akin to vehicles moving in an orderly fashion on a superhighway. Because of zero resistance, superconducting materials can save huge amounts of energy, and be used to make highly efficient electrical appliances.

The problem is that superconductivity, ever since it was first discovered in 1911, has only been observed at very low temperatures, somewhere close to what is called absolute zero (0°K or -273.15°C). In recent years, scientists have been able to find superconductive materials at temperatures that are higher than absolute zero but, in most cases, these temperatures are still below -100°C and the pressures required are extreme. Creating such extreme conditions of temperature and pressure is a difficult task. Therefore, the applications of superconducting materials have remained limited as of now.

The IISc scientists have reported that some of their samples of nanoparticles of gold-silver composite material displayed superconductivity at 13°C, and under normal atmospheric pressure. Further, this material had the potential to show superconductivity at even higher temperatures under some special conditions, up to as much as 75°C.

They have provided evidence of these samples displaying two fundamental properties of a superconductor — zero resistance to electrical current, and diamagnetism. The latter is a property opposite to normal magnetism that we are used to. A diamagnetic substance repels an external magnetic field, in sharp contrast to normal magnetism, or ferromagnetism, under which a substance is attracted by an external magnetic field.

The scientists have now reported that these two properties were observed simultaneously, in the same sample of the material. These two properties had been observed last year too, but in different samples.

The scientists shared their findings on the same online platform last month, triggering fresh excitement in scientific circles. Skepticism has been subdued this time, they say, and add there is a palpable sense of something big on the horizon. However, by the scientists’ own admission, some legitimate questions about the data and the behaviour of the material remain unaddressed.

On June 6, the group put out more data and information on the experiments in response to queries that were raised. The matter would be settled only when their paper is finally published. As of now, no one knows how long that is going to take. Considering the scale of the finding, it is likely to undergo several layers of peer review.