Development of a new pressure quenching technique demonstrates superconductivity in iron selenide crystals without pressure


In a decisive next step towards room temperature superconductivity at ambient pressure, Paul Chu, founding director and senior scientist at the Texas Center for Superconductivity at the University of Houston (TcSUH), Liangzi Deng, Scientific Assistant Professor of Physics at TcSUH, and her colleagues from TcSUH conceived and developed a pressure quenching (PQ) technique that maintains the pressure enhanced and / or induced high transition temperature (Tc) phase even after removal of the applied pressure that creates that phase.

Pengcheng Dai, professor of physics and astronomy at Rice University and his group, and Yanming Ma, dean of the College of Physics at Jilin University, and his group contributed to successfully applying the possibility of pressure quenching technology in a model of a high-temperature superconductor demonstrate iron selenide (FeSe). The results were published in the journal Proceedings of the National Academy of Sciences UNITED STATES.

“We derived the pressure quenching method from Francis Bundy’s formation in 1955 of the man-made diamond from graphite and other metastable compounds,” Chu said. “Graphite turns into a diamond when subjected to high pressure at high temperatures. Subsequent rapid pressure quenching or pressure relief leaves the diamond phase intact without pressure.”

Chu and his team applied the same concept to a superconducting material with promising results.

“Iron selenide is considered to be a simple, high-temperature superconductor with a transition temperature (Tc) for transition to a superconducting state at 9 Kelvin (K) at ambient pressure,” said Chu.

“When we applied pressure, the Tc increased to ~ 40 K, more than four times that at ambient temperature, which allowed us to clearly distinguish the superconducting PQ phase from the original non-PQ phase. We then tried to keep the high pressure reinforced superconducting phase after removing the pressure using the PQ method and it turns out we can. “

Dr. Chu and colleagues are bringing the scientists one step closer to realizing the dream of room temperature superconductivity at ambient pressure, which was recently described in hydrids only under extremely high pressure.

Superconductivity is a phenomenon that was discovered by Heike Kamerlingh Onnes in 1911 by cooling mercury below its transition temperature of 4.2 K, which can be achieved with the help of the rare and expensive liquid helium. The phenomenon is profound due to the superconductor’s ability to exhibit no resistance when electricity moves through a superconducting wire and its expulsion of the magnetic field generated by a magnet. Its enormous potential in the energy and transportation sector was then immediately recognized.

In order to operate a superconducting device, it must be cooled below its Tc, which requires energy. The higher Tc, the less energy is required. Hence, increasing Tc with the ultimate goal of a room temperature of 300K has been the driving force behind superconductivity scientists since its discovery.

Contrary to the prevailing opinion at the time that Tc cannot exceed 30’s K, Paul Chu and colleagues discovered superconductivity in a new family of compounds at 93 K in 1987, which could be achieved by the mere use of the inexpensive, inexpensive industrial coolant of liquid nitrogen . The Tc has since been used by Chu et al. continuously increased to 164 K. and other subsequent groups of scientists. Recently, Dias et al. reached a Tc of 287 K. from Rochester University in carbon disulfide under 267 gigapascals (GPa).

In short, increasing Tc to room temperature is actually within reach. However, the future scientific and technological development of hydrides requires the characterization of materials and the manufacture of devices at ambient pressure.

“Our method enables us to make the material with higher Tc superconducting without pressure. It even allows us to keep the non-superconducting phase that only exists in FeSe above 8 GPa in the environment. There is no reason why the technique cannot be applied equally to the hydrides, which have shown signs of superconductivity at Tc near room temperature. “

The achievement brings the academic community closer to room temperature superconductivity (RTS) without pressure, which would mean ubiquitous practical applications for superconductors in the medical field, from energy transmission and storage to transportation, with implications for any use of electricity.

Superconductivity as a means of improving power generation, storage and transmission is not a new idea, but more research and development will be needed to become widespread before room temperature superconductivity becomes a reality. As there is no electrical resistance, energy can be generated, transmitted and stored without loss – an enormous cost advantage. Current technology, however, requires that the superconducting device be kept at very low temperatures in order to maintain its unique condition, which still requires additional energy as an overhead cost, not to mention the potential for accidental failure of the cooling system. Therefore, an RTS superconductor with no additional pressure to maintain its advantageous properties is a necessity to advance more practical applications.

The properties of superconductivity also pave the way for a competitor to the famous high-speed train seen across East Asia: a maglev train. The abbreviation for “maglev train”, the first maglev train built in Shanghai in 2004, has successfully expanded use in Japan and South Korea and is being considered for commercial operation in the United States. At top speeds of 375 miles per hour, cross-country flights see a fast competitor in the maglev train. A room temperature superconductor could help Elon Musk achieve his dream of a “hyperloop” that can travel at a speed of 1,000 miles per hour.

This successful implementation of the PQ technique in room temperature superconductors, discussed in Chu and Deng’s article, is critical to enabling superconductors for ubiquitous practical applications.

Now the riddle of RTS at ambient pressure is even closer to being solved.

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