Type: Research Essays
Sample donated: Doyle Palmer
Last updated: December 30, 2019
Superconductors are right at the cutting edge of modern physics; their extensive range of uses in the real world and their potential to transmit power with highly minimal losses is why they are so exciting and desirable. In this essay, I will outline what superconductors are, followed by a brief history and explanation of how they work.
Then, I will go through the potential benefits and uses, current research and potential issues we may face when dealing with superconductors. As a result, I shall have summarised superconductors in terms of their uses and possibilities. Superconductors are essentially elements, metallic alloys or compounds, which are capable of conducting electricity at a low temperature, presently a very low one, with zero resistance. Once conductivity has begun, if the superconductor is in a closed loop, this will allow for electrical current to be conducted in this loop forever, making it ‘the closest thing to perpetual motion in nature’ (Reference superconductors.org) We have known about superconductivity for a long period – the discovery began in 1911 when Kamerling Onnes, a Dutch Physicist, found that for a mercury sample, the resistance disappeared suddenly, below what is known as a critical temperature. This temperature is defined as the temperature where electrical resistivity of a metal falls to zero (http://hyperphysics.phy-astr.
gsu.edu/hbase/Solids/scond.html, 2017). Following this, he further found that relatively small magnetic fields have the ability to stop the effects of superconductivity and that this critical magnetic field is a function of temperature. In addition to these discoveries, the German researchers Walther Meissner and Robert Oschenfield found in 1933 that a superconducting material, below its critical temperature, will repel a magnetic field, with this now being known as the Meissner effect. Meissner; Oschenfield, 1933). This effect is in fact so strong that a magnet can in fact be levitated above a magnetic field.
Since then, the aim has been to attempt to work out how exactly superconductivity occurs, especially at high temperatures. A more recent breakthrough, in 1986, was Alex Muller and George Bendorz created a ‘brittle ceramic compound’ (http://www.superconductors.org/History.htmwhich, 2017) capable of superconductivity at 30 Kelvin, the highest yet known temperature, at the time, at which superconductivity can occur. The significance of this discovery was that the superconductor was a ceramic, which are usually insulators. In 1987, a 92K superconductor was found, one that was able to super conduct at a temperature warmer than liquid nitrogen, for the first time.
htmwhich, 2017), (Cooper, Feldman, 2011) Superconductors can be divided into two types: Type I and Type II superconductors. The type I superconductors consist of pure metals, with one exception of an alloy known as tantalum silicide, which at low temperatures, will exhibit the properties of superconductivity (these being zero resistivity and the ability of expelling the magnetic field from within the conductor itself). These types of superconductors can be well explained via the BCS Theory (Bardeen, Cooper, Leon, 1957). This theory was able to explain how superconductors operate at temperatures near 0 Kelvin. Type II superconductors, on the other hand, are mainly comprised of alloys or metallic compounds and these generally achieve higher critical temperatures than type I superconductors.
The reason for this is not well known, but is to do with the crystalline structure and its layering in a planar formation, Type II superconductors are generally of more practical use than type I, since type I superconductors have a much smaller magnetic field at their critical temperature, which dissapears suddenly at this point as temperature rises. Type II conductors have the ability to maintain their superconductive state to higher temperatures. The BCS Theory, although good at explaining superconductivity at low temperatures, at higher temperatures this theory is a less adequate explanation.
html, 2017), (http://www.superconductors.org/History.html, 2017). The BSC Theory explains the rapid drop to zero in resistivity when the temperature of a superconductor falls below Tc.
A key part of this theory is that electons are paired near to the Fermi level into Cooper pairs, via interaction with the crystal lattice, due to a mild attraction between electrons resulting from vibrations in the lattice. This is know as a phonon interaction. Pairs of electrons behave somewhat differently from single electrons and act more like bosons, and condense into the same energy level.
Electron pairs leave an energy gap above them