In Search of Room-Temperature Superconductors

Imagine a world in which magnetic levitation (maglev) trains are commonplace, computers are lightning-fast, power cables have little loss, and new particle detectors exist. This is the world in which room-temperature superconductors are a reality. So far, this is a dream of the future, but scientists are closer than ever to achieving room-temperature superconductivity. What Is Room-Temperature Superconductivity? A room temperature superconductor (RTS) is a type of high-temperature superconductor (high-Tc or HTS) that operates closer to room temperature than to absolute zero. However, the operating temperature above  0  °C (273.15 K)  is still well below what most of us consider normal room temperature (20  to  25  Ã‚ °C). Below the critical temperature, the superconductor has zero electrical resistance and expulsion of magnetic flux fields. While its an oversimplification, superconductivity may be thought of as a state of perfect electrical conductivity. High-temperature superconductors exhibit superconductivity above  30  K (−243.2  Ã‚ °C). While a traditional superconductor must be cooled with liquid helium to become superconductive, a high-temperature superconductor can be cooled using liquid nitrogen. A room-temperature superconductor, in contrast, could be cooled with ordinary water ice.   The Quest for a Room-Temperature Superconductor Bringing up the critical temperature for superconductivity to a practical temperature is a holy grail for physicists and electrical engineers. Some researchers believe room-temperature superconductivity is impossible, while others point to advances that have already surpassed previously-held beliefs. Superconductivity was discovered in 1911 by  Heike Kamerlingh Onnes in solid mercury cooled with liquid helium (1913 Nobel Prize in Physics). It wasnt until the 1930s that scientists proposed an explanation of how superconductivity works. In 1933, Fritz and Heinz London explained the Meissner effect, in which a superconductor expels internal magnetic fields. From Londons theory, explanations grew to include the  Ginzburg-Landau theory (1950) and microscopic BCS theory (1957, named for Bardeen, Cooper, and Schrieffer). According to the BCS theory, it seemed superconductivity was forbidden at temperatures above 30 K. Yet, in 1986,  Bednorz and Mà ¼ller discovered the first high-temperature superconductor, a lanthanum-based cuprate perovskite material with a transition temperature of 35 K. The discovery earned them the 1987 Nobel Prize in Physics and opened the door for new discoveries. The highest temperature superconductor to date, discovered in 2015  by Mikhail Eremets and his team, is sulfur hydride (H3S). Sulfur hydride has a transition temperature around 203 K (-70  °C), but only under extremely high pressure (around 150 gigapascals). Researchers predict the critical temperature might be raised above  0  Ã‚ °C  if the sulfur atoms are replaced by phosphorus, platinum, selenium, potassium, or tellurium  and still-higher pressure is applied. However, while scientists have proposed explanations for the behavior of the sulfur hydride system, they have been unable to replicate the electrical or magnetic behavior. Room-temperature superconducting behavior has been claimed for other materials besides sulfur hydride. The high-temperature superconductor yttrium barium copper oxide (YBCO) might become superconductive at 300 K using infrared laser pulses. Solid-state physicist Neil Ashcroft predicts solid metallic hydrogen should be superconducting near room temperature. The Harvard team that claimed to make metallic hydrogen reported the Meissner effect may have been observed at 250 K. Based on exciton-mediated electron pairing (not phonon-mediated pairing of BCS theory), its possible high-temperature superconductivity might be observed in organic polymers under the right conditions. The Bottom Line Numerous reports of room-temperature superconductivity appear in scientific literature, so as of 2018, the achievement seems possible. However, the effect rarely lasts long and is devilishly difficult to replicate. Another issue is that extreme pressure may be required to achieve the Meissner effect. Once a stable material is produced, the most obvious applications include the development of efficient electrical wiring and powerful electromagnets. From there, the sky is the limit, as far as electronics is concerned. A room-temperature superconductor offers the possibility of no energy loss at a practical temperature. Most of the applications of RTS have yet to be imagined. Key Points A room-temperature superconductor (RTS) is a material capable of superconductivity above a temperature of 0  °C. Its not necessarily superconductive at normal room temperature.Although many researchers claim to have observed room-temperature superconductivity, scientists have been unable to reliably replicate the results. However, high-temperature superconductors do exist, with transition temperatures between  Ã¢Ë†â€™243.2  Ã‚ °C  and  Ã¢Ë†â€™135  Ã‚ °C.Potential applications of room-temperature superconductors include faster computers, new methods of data storage, and improved energy transfer. References and Suggested Reading Bednorz, J. G.; Mà ¼ller, K. A. (1986). Possible high TC superconductivity in the Ba-La-Cu-O system. Zeitschrift fà ¼r Physik B. 64 (2): 189–193.Drozdov, A. P.; Eremets, M. I.; Troyan, I. A.; Ksenofontov, V.; Shylin, S. I. (2015). Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system. Nature. 525: 73–6.Ge, Y. F.; Zhang, F.; Yao, Y. G. (2016). First-principles demonstration of superconductivity at 280 K in hydrogen sulfide with low phosphorus substitution. Phys. Rev. B. 93 (22): 224513.Khare, Neeraj (2003). Handbook of High-Temperature Superconductor Electronics. CRC Press.Mankowsky, R.; Subedi, A.; Fà ¶rst, M.; Mariager, S. O.; Chollet, M.; Lemke, H. T.; Robinson, J. S.; Glownia, J. M.; Minitti, M. P.; Frano, A.; Fechner, M.;  Spaldin, N. A.; Loew, T.; Keimer, B.; Georges, A.; Cavalleri, A. (2014). Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5.  Nature.  516  (7529): 71–73.   Mourachkine, A. (2004).  Room-Temperature Superconductivity. Cambridge International Science Publishing.