In this Thought Leader interview with AZoM's G.P. Thomas, Professor Paul Chu, director of the Texas Center for Superconductivity at the University of Houston, talks about his work on high-temperature ceramic superconductors. In 1987, Professor Chu's team were the first to create a superconductor with a critical temperature (Tc) above the boiling point of liquid nitrogen.
What is superconductivity? Could you briefly explain the scientific theory behind this?
Superconductivity is the property of a superconductor that displays zero resistance and expels externally applied magnetic field when it is cooled below a characteristic temperature known as the superconducting transition temperature (Tc). As a result, it can be used to make cable for energy transmission, generators for energy generation, rings for energy storage, fault current limiters and transformers for improved energy quality, faster and quieter magnetic levited trains and low-cost and high-mobility MRI machines, etc., all with efficiencies unmatched by their conventional counterparts. Because superconductivity is a quantum phenomenon, it allows one to use it to make ultra-sensitive devices and ultra-fast switches for various applications. To sum it up, superconductivity will impact our lives profoundly whenever we use electricity when the technology is perfected.
In 1987, you and your team achieved superconductivity above 77 degrees Kelvin – could you please explain a little about the background research involved in this and how this was achieved?
Before 1986, the highest Tc was at 23.2 K in a Nb3Ge intermetallic compound discovered in 1973, and the theory predicted that the Tc could not exceed 30'S K. in 1986, Muller and Bednorz of IBM set a new record by observing a Tc up to 35 K in a Ba-doped La-Cu-O oxide for the so-called 214 phase. Unfortunately it still needed liquid helium to cool. The report was initially received with sketicism except for a few, including my group, since we had shown that the theoretical basis for a 30 K Tc ceiling was not valid in the late 70's and early 80's. We decided to examine oxide phases different from the 214 phase and were lucky enough to discover the so-called 123 phase with a Tc of 93 K, above the liquid nitrogen boiling point of 77 K, making liquid nitrogen cooling possible.
Why is the boiling point of liquid nitrogen an important reference point for the transition temperature of a superconductor?
This is because liquid nitrogen is plentiful in air, an industrial by-product, and an effective coolant. It is far less expensive and easier to handle than liquid helium, so if a superconductor can be cooled by this material, it makes it much easier to work with in practical applications.
How has this been applied over the last 25 years?
Many prototype devices have been constructed and tested successfully to exhibit superior performance to their non-superconducting counterparts, such as motors, generators, transformers, fault-current limiters, magnetic imagers for medical diagnostics, magnetic sensors, etc.
How are YBaCuO superconductors unique?
They carry higher super currents in stronger magnetic field for power and magnet applications, are easier to fabricate especially in thin film form for electronic device applications, are more robust physically and chemically and less expensive. They are therefore the undisputed first choice for application and scientific study among all high temperature superconductors discovered so far.
High-temperature superconductors have been produced from a variety of materials – what are the key differences between copper-oxide superconductors and Iron-based superconductors?
They display a layered structure, a strong electron correlation, an intriguous relation to magnetism.
What industry sectors can superconducting materials be utilised in?
A very wide range of areas, such as energy, medicine, transportation, electronics, and defense.
The 25th anniversary of this achievement was recently celebrated at the University of Houston – could you please tell us more about this day and who attended?
The day celebrated the 25th Anniversary of the discovery of YBCO as well as the 25th Anniversary of the establishment of the Texas Center for Superconductivity at the University of Houston. We tried to structure an event that would serve to commemorate the discovery of new ideas and innovations in materials, including HTSs, and present groundbreaking research in a manner that a general audience would understand.
The speakers, consisting of Nobel laureates, National Academy members and U.S. and international leaders from academia, government and industry shared their thoughts on past, present and future materials research, but from a personal perspective, taking questions from the audience. About 400 academicians, city/state/national officials, community leaders, teachers and students attended the symposium.
A special luncheon was also held for 200 special Friends of TcSUH, including members of Congress, State and City government, members of leading U.S. and international government and academic institutions, distinguished alumni who now hold prominent positions in industry, academia and government, members of the philanthropic community, etc.
How do you personally see superconductivity research progressing in the future?
It is bright and exciting with a never-ending scientific and technological frontier. I believe God has been kinder to physicists than to mountaineers, because for the latter once Everest is reached, the excitement ceases.
About Paul Chu
Prof. Paul Ching-Wu Chu is the T.L.L. Temple Chair of Science and Professor of Physics at the University of Houston. He is founding director of the Texas Center for Superconductivity at the University of Houston (TcSUH) and now serves as its Chief Scientist. Prof. Chu received his Ph.D. degree at the University of California at San Diego. He has received numerous awards and honors for his outstanding work in superconductivity, including the U.S. National Medal of Science and the International Prize for New Materials. He was an invited contributor to the White House National Millennium Time Capsule at the National Archives in 2000 and was selected the Best Researcher in the U.S. by US News and World Report in 1990. He is a member of the U.S. National Academy of Sciences, American Academy of Arts and Sciences, Chinese Academy of Sciences (foreign member), Academia Sinica and The Academy of Sciences for the Developing World; and a Fellow of the Russian Academy of Engineering. His research activities extend beyond superconductivity to magnetism and dielectrics. His work has resulted in the publication of more than 590 papers in refereed journals.
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