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Graphic illustration of a superconducting cuprate system. Credit: Cockrell School of Engineering, University of Texas at Austin
Solving the mystery of high temperature superconductivity, especially in copper oxide materials, remains one of the most mysterious challenges of modern physics in the solid state. But an international team of engineers and scientists may have made progress in its understanding.
Superconductors are materials that acquire unique physical properties when they are cooled to extremely low temperatures. They stop resisting an electric current, allowing the current to pass freely without any loss of energy. Superconductors are used in technologies such as MRI machines, electric motors, wireless communication systems and particle accelerators. Although thousands of examples of superconducting materials are known to the scientific community, many questions remain as to why and how superconductivity occurs. A new search can provide an answer.
A research team including Jianshi Zhou, professor-researcher in mechanical engineering at the Cockrell School of Engineering and a member of the University of Texas at the Texas Materials Institute in Austin, confirmed the existence of a transition phase at a temperature close to absolute zero. higher than the temperature required by many superconductors, in superconducting materials based on copper oxide (or cuprate). The team believes that it could be superconductivity during the phase transition, the "quantum critical point". The results were published in a recent issue of the journal Nature.
The study measured the effects of heat on two cuprate systems known as superconductors: Eu-LSCO and Nd-LSCO, two crystalline systems based on copper oxide. Both materials were cooled to their critical temperature points, while large magnetic fields were used to suppress their superconductivity. The thermodynamic signatures obtained during the experiment confirmed the existence of the phase of "quantum criticality" in the analyzed examples.
"Quantum criticality has been proposed as a potential factor to facilitate superconductivity in cuprate systems," said Zhou. "Our study confirms that this is the case."
Zhou is the only US researcher to participate in the study and one of the few engineers in the world with the expertise to develop and analyze crystalline systems in cuprate, one of the most commonly used superconductors.
Engineers often classify materials according to their resistance to the flow of electric currents. It is a property measured by observing the behavior of electrons. Metals like copper – a key component in the wires connecting the chargers of our smartphones, microwaves, light bulbs and many others to electrical outlets – are made up of electrons that move freely around its atomic structure. This offers low resistance to electric currents, a property that makes a driver strong.
Resistance, no matter how weak, is undesirable in conductive materials because the energy used to resist turns into heat and is technically wasted. In a perfect world, the cables would be made of a material with zero resistance to electrical current. This is where superconductors come into play. However, as all known superconductors must be cooled to extremely low temperatures, they are difficult to use regularly in practical applications. In the end, engineers and scientists around the world continue to look for superconducting materials that can be used at much higher temperatures in the hope of reaching ambient temperature. Every discovery made brings researchers closer together.
"Understanding why these materials become superconductors will lead us to this holy grail of superconductors at room temperature," Zhou said. "It's only a matter of time, hopefully."
Explore further:
Superconductors: resistance is futile
More information:
B. Michon et al., Thermodynamic signatures of quantum criticality in cuprate superconductors, Nature (2019). DOI: 10.1038 / s41586-019-0932-x
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