Jan 28 2019
Scientists at the University of Houston have come up with an innovative way to increase the transition temperature of superconducting materials, boosting the temperature at which the superconductors can function.
Researchers Liangzi Deng, left, and Paul Chu, founding director of the Texas Center for Superconductivity at UH, examine a miniature diamond anvil cell, or mini-DAC, which is used to measure superconductivity. (Image credit: Audrius Brazdeikis)
The outcomes of the study, published in the Proceedings of the National Academy of Sciences, propose a previously uninvestigated approach for realizing higher temperature superconductivity, which provides several potential advantages to energy generators and consumers.
In contrast to conventional transmission materials that lose nearly 10% of the energy between the generating source and the end user, in superconducting materials, electric current can pass through without any resistance. Discovering superconductors with the ability to operate at or near room temperature—existing superconductors mandate the use of a cooling agent—could enable utility companies to offer more electricity without any increase in the quantity of fuel needed, thereby minimizing their carbon footprint and enhancing the efficiency and reliability of the power grid.
Although there was an exponential increase in the transition temperature for the materials tested using the new technique, it remained below room temperature. However, according to Paul C.W. Chu, chief scientist at the Texas Center for Superconductivity at UH (TcSUH) and corresponding author of the paper, the technique provides a completely new approach to solve the challenge of finding superconductors that operate at a higher temperature.
Chu, who is also a physicist and TLL Temple Chair of Science at UH, stated that the existing record for a stable, high-temperature superconductor, set in 1994 by his team, is 164 K, or about −164 °F. That was a mercury-based superconductor; the bismuth materials tested for the new study are less toxic, and unanticipatedly reach a transition temperature of >90 K, or about −297 °F, following the initial predicted drop to 70 K.
The study exploits the well-known principle that it is possible to predict a superconductor’s transition temperature by gaining insights into the relationship between that temperature and doping—a technique which involves adding small amounts of an element that can alter its electrical properties to change the material—or between that temperature and physical pressure. In principle, the transition temperature increases up to a specific point and then starts to drop, even with a continuous increase in the pressure or doping.
Liangzi Deng, a scientist at TcSUH working with Chu and first author of the paper, proposed the concept of raising the pressure above the levels previously explored to verify whether there would be again an increase in the superconducting transition temperature after dropping.
It worked!
This really shows a new way to raise the superconducting transition temperature.
Liangzi Deng, Researcher, Texas Center for Superconductivity at The University of Houston
The Fermi surface of the tested compounds was changed by the higher pressure, and Deng stated that the researchers considered that the pressure alters the electronic structure of the material.
The width of the superconductor samples tested by the researchers was less than one-tenth of 1 mm; according to them, it was difficult to detect the superconducting signal of such a tiny sample through magnetization measurements, the most conclusive test for superconductivity. In the recent past, Deng and his teammates in Chu’s lab devised an ultrasensitive magnetization measurement method that enables them to sense a very small magnetic signal from a superconducting sample under pressures of above 50 GPa.
Deng found that in these tests, the scientists did not notice a saturation point—in other words, there will be a continuous increase in the transition temperature with the increase in pressure.
The researchers tested various bismuth compounds known to exhibit superconducting properties and noted that the new technique considerably increased the transition temperature of each compound. According to them, it was not clear whether the method would hold good for all superconductors; however, it is promising that it worked on three different formulations.
However, it is not practical to boost superconductivity through high pressure for real-world applications. According to Chu, the next step will be to discover a means to realize the same effect without pressure and with chemical doping.