Unlike an ordinary metallic conductor, that its resistance decreases gradually as its temperature is lowered not quite reaching zero resistance even down at absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero.
This phenomenon was discovered in 20th century when liquid helium was discovered. Liquid helium evaporates in 4 K. Most metals and some alloys become superconductor under 25K. For a while nobody knew the exact reason behind this behavior! After 50 years, J. Bardeen, L. Cooper, and J. R. Schrieffer showed based on the principles of quantum mechanics that if somehow an attraction force is developed between electrons the superconducting state is created. This attraction force is therefore the physical foundation of superconductivity. The question is how electrons can be made to attract each other and the answer is that the crystal with its nuclei makes it possible.
In order to understand the origin of the attraction force, imagine two billiard balls that don’t attract or repulse each other. If you drop one of these balls on a stretched level fabric it bends the fabric downward. If you now drop the second ball close enough to the first ball the bend the fabric would cause one to move toward the other. This is in fact an attraction force between the two balls mediated by the fabric. The crystal with its nuclei play the role of the fabric and an electron passing through would attract the nuclei toward it and those in return attract other electrons. This is the attraction force, which has been shown to create the so-called low temperature superconductivity. This attraction is small and limited and that’s the reason why superconductivity occurs only under 25 K by this mechanism. Thermal energy above 25 K is large enough to cancel the superconducting effects of this attraction.
Quite surprisingly in 1986, some superconductors were discovered that had critical temperatures above 77K, the boiling point of liquid Nitrogen. We call these materials the “High Temperature Superconductors”. Since then nobody has scientifically explained this phenomenon. The problem has become more complicated because these materials are not only superconductors at high temperatures but they exhibit some unexplained extra behaviors as well. It seems that any theory that explains high temperature superconductivity needs to address these so-called exotic behaviors as well. Over the past 30 years such a theory has eluded scientists and some publicly state that they have lost faith in the possibility of finding the exact cause or an all encompassing theory explaining all the characteristics of high temperature materials.
Dr. Farshid Raissi, professor of Electronics at at K.N.Toosi University of Technology, believes he might have found the holy grail of high temperature superconductivity. “I have come up with a potential that can answer all of the above questions. Furthermore, it tells us what we need to do to obtain superconductors at room temperature” Dr. Raissi says.
“As a matter of fact, invention or discovery of room temperature superconductivity can change everything! Transportation would be completely revolutionized, as well as power transmission and motor and generator efficiencies. One immediate affect would be a huge step toward the prevention of global warming and destructive climate changes.”
“I was teaching modern physics at KNTU twenty years ago when this idea came to my mind for the first time: what if we should find the attraction force responsible for high Tc superconductivity in the principles of relativity instead of quantum mechanics?” Farshid Raissi asked.
Afterwards, he checked out a book about relativity and electromagnetism and he tracked down a hint that helped him to reach an important result. The hint said: “ The electric field of a static charges particle is different from a moving particle. The electric field decreases in the direction of motion and increases in its perpendicular directions.” At first, the hint was vague and he was dubious about its relationship with superconductivity. But suddenly it occurred to him that since the nuclei are stationary and electrons are moving inside a solid their corresponding electric fields would not cancel each other and attraction forces can occur in some materials. This was an important realization that has lead him to finalize a well-rounded theory that claims to explain all the high temperature superconductivity characteristics.
In order to understand the new attraction force consider the following example. The electric potential around a charged particle is spherically symmetric or it looks like a balloon. When it moves in a certain direction it decreases in the direction of motion and its opposite direction and increases in all other directions. To visualize what happens imagine pushing with both hands in opposite sides of this balloon. This is the shape the potential takes as a result of its motion. Now this new potential must be added to the potential of nuclei that is symmetric. If we add these two potentials they won’t cancel each other. There will be an attraction force in the direction of motion and a repulsion force in perpendicular directions. It can be shown that the combination of these attraction and repulsion force can cause all the characteristics of known high Tc materials. For more information readers are encouraged to visit AIP Advances 9, 075022 (2019); https://doi.org/10.1063/1.5098464
This theory predicts that if the materials involved in superconductivity only have p orbitals at their highest shells and the Fermi speed of electrons are increased by a factor of 5 compared to existing material achieving room temperature superconductivity is possible by this mechanism.