Superconductivity was discovered in 1911, but its properties and characteristics have not yet been fully studied. New research on nanowires is helping to understand how this phenomenon is lost.
The problem of keeping drinks cold in hot summer is a classic phase change lesson. They must be studied, the substance must be heated and the changes in its properties must be observed. When you reach the so-called critical point, add water or heat - and watch how the substance turns into gas (or steam).
Now imagine that you have cooled everything to very low temperatures - so much so that all thermal effects are gone. Welcome to quantum reality, where pressure and magnetic fields do not affect the emergence of new phases in any way! This phenomenon is called quantum phase transition. Unlike a conventional transition, a quantum transition forms completely new properties, such as superconductivity (in some materials).
If you apply voltage to a superconducting metal, electrons will travel through the material without resistance, and electric current will flow indefinitely, without slowing down or generating heat. Some metals become superconducting at high temperatures, which is important in the case of power transmission and data processing based on superconductors. Scientists discovered this phenomenon 100 years ago, but the mechanism of superconductivity itself remains a mystery, since most materials are too complex to understand the physics of quantum phase transition in detail. So the best strategy in this case is to focus on learning less complex model systems.
Physicists at the University of Utah have found that superconducting nanowires made from a molybdenum-germanium alloy undergo quantum phase transitions from superconducting to ordinary metal when placed in an ordinary magnetic field at low temperatures. This study first revealed the microscopic process by which a material loses its superconductivity: a magnetic field breaks up pairs of electrons - Cooper pairs interacting with other pairs of the same type - and they experience a damping force from unpaired electrons in the system.
The research is detailed in a critical theory proposed by Adrian Del Maestro, assistant professor at the University of Vermont. The theory accurately described how the evolution of superconductivity depends on the critical temperature, the magnitude of the magnetic field and orientation, the cross-sectional area of the nanowire, and the microscopic characteristics of the material from which it is made. This is the first time in the field of superconductivity that all the details of a quantum phase transition are predicted by theory, confirmed on real objects in the laboratory.
“Quantum phase transitions may sound very exotic, but they are observed in many systems - from the centers of stars to atomic nuclei, as well as from magnets to insulators, - said Andrey Rogachev, assistant professor at the University of Utah and lead author of the study. “Once we understand quantum vibrations in this simpler system, we can talk about every detail of the microscopic process and apply it to more complex objects.”
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