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endsofuniverse
Zero resistance is an ideal case and we can never achieve an ideal circumstance.However we can get close to the ideal condition.
It is the superconductivity that leads us to the resistance close to zero.
1. What is the superconducting state?
The exact definition of the superconducting state will be given in the following chapter. Here we discuss a bird’s-eye view of the superconducting state. First, one question: would you be able to notice the difference in taste between two glasses of your preferred drink—soft or hard, whatever—in one of which a 10−4 part, i.e. 0.01%, is replaced by another drink? I do not think so.However, it is not the case for a superconductor (not literally, of course).
In some metals for example, the superconducting state occurs due to the presence of a 10−4 fraction of “abnormal” electrons, while the other 99.99% free (conduction) electrons remain absolutely normal. The correlated behavior of the small fraction of these “abnormal” electrons overwhelms the rest.Amazing, is it not? Due to the presence of these “abnormal” electrons, the metal is no longer a metal but a superconductor, losing its ability to resist to a small-magnitude electrical current. The presence of normal (conduction) electrons is completely masked by that of the “abnormal” electrons, as if the normal electrons were not existing at all. (Of course, we talk only about electron transport properties of a metal; the crystal structure of a metal is almost unchanged below the critical temperature, i.e. when a metal becomes superconducting.)
* What does the superconducting state literally mean?
In the superconducting state, THERE IS NO FRICTION.
* In the real world, what does it mean?
If friction were absent, Earth would be ideally round, no buildings, no clothes, and I am afraid that the living matter,including us, would not exist at all.
The superconducting state is a quantum state occurring on a macroscopic scale. In a sense, the superconducting state is a “bridge” between the microworld and the macroworld. This “bridge” allows us to study the physics of the microworld directly. This is one of the reasons why superconductivity, driven only by a 10−4 fraction of “abnormal” electrons, has attracted the attention of so many scientists since its discovery in 1911 (thus, more than 90 years of intensive research!). Between 1911 and 1957, many best minds tried to unravel the mystery of this state caused only by 0.01 % of conduction electrons.
How do normal electrons in a superconductor become “abnormal”?
At the Big Bang, Nature has created two types of elementary particles: bosons and fermions. Bosons have an integral spin, while fermions a half-integral spin. As a consequence, bosons and fermions conform to different statistics. Electrons are fermions with a spin of 1/2 and obey the Fermi-Dirac statistics. In a superconductor, two electrons can form a pair which is already a boson with zero spin (or a spin equal to 1). These electron pairs conform to the Bose-Einstein statistics and, being in a phase, can move in a crystal without friction. This is how, in a classical superconductor, a tiny fraction 0.01 % of all conduction electrons becomes “abnormal.” Simple, is it not?
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