Superconducting materials can transport electrons with no resistance, and hence release no heat, sound, or other energy forms. Superconductivity occurs at a specific material's critical temperature (Tc). As temperature decreases, a superconducting material's resistance gradually decreases until it reaches critical temperature. At this point resistance drops off, often to zero, as shown in the graph at right.
At the present time, most materials must achieve an extremely low energy state via low temperatures and/or high pressures in order to achieve superconductivity. While research superconductors that are effective at higher temperatures are in development, superconductivity is typically possible only with expensive, inefficient cooling processes.
Superconductors exhibit unique features other than their ability to perfectly conduct current. For example, many expel magnetic fields during the transition to the superconducting state. This is due to the Meissner effect by which superconducting materials set up electric currents near their surface at Tc, therefore canceling the fields within the material itself. A stationary magnet on a superconductor demonstrates this effect: as the superconductor cools through its critical temperature, the expulsion of magnetic flux from the conductor causes the magnet to levitate above the material.\cite{globalspec2017}
Superconductors
Trains that float, faster
computers that can store more data, and
electric power that zaps into your home wasting less
energy are just a few of the benefits promised by superconductors—materials that offer little or no
resistance to
electricity. You're probably used to the idea that conductors (such as
metals) carry electricity well, while insulators (such as
plastics) barely let it pass through them at all. But how much do you know about superconductors that eliminate resistance almost entirely when you cool them down to very low temperatures?
How resistance changes with temperature
It's a little bit misleading to divide materials into conductors and insulators. It's much more accurate to say that all materials conduct electricity, under the right conditions, but some conduct more easily than others. When we say a metal conducts electricity well, we really mean it offers little or no resistance when you try to make a current flow through it; when we say
plastics insulate well, we're actually saying that they put up high
resistance to electric currents. Resistance is often a much more useful concept than trying to divide materials into "conductors" and "insulators".
One of the interesting things about resistance is how it changes as you change the temperature. Suppose you have a piece of
gold wire in an electrical circuit. Gold is one of the best conductors there is: it shows very little resistance to electricity. But increase its temperature and it puts up much more resistance. Why? Broadly speaking, the higher the temperature, the more thermal vibrations there are inside the gold's crystalline structure and the harder electrons (the negatively charged particles inside
atomsthat carry electric currents) will find it to flow through. Conversely, if you cool gold down, you reduce the vibrations and make it easier for electrons to flow.