Superconductor Definition, Types, and Uses

A superconductor is an element or metallic alloy which, when cooled below a certain threshold temperature, the material  dramatically loses all electrical resistance. In principle, superconductors can allow electrical current to flow without any energy loss (although, in practice, an ideal superconductor is very hard to produce). This type of current is called a supercurrent. The threshold temperature below which a material transitions into a superconductor state is designated as Tc, which stands for critical temperature. Not all materials turn into superconductors, and the materials that do each have their own value of Tc. Types of Superconductors Type I superconductors act as conductors at room temperature, but when cooled below Tc, the molecular motion within the material reduces enough that the flow of current can move unimpeded.Type 2 superconductors are not particularly good conductors at room temperature, the transition to a superconductor state is more gradual than Type 1 superconductors. The mechanism and physical basis for this change in state is not, at present, fully understood. Type 2 superconductors are typically metallic compounds and alloys. Discovery of the Superconductor Superconductivity was first discovered in 1911 when mercury was cooled to approximately 4 degrees Kelvin by Dutch physicist Heike Kamerlingh Onnes, which earned him the 1913 Nobel Prize in physics. In the years since, this field has greatly expanded and many other forms of superconductors have been discovered, including Type 2 superconductors in the 1930s. The basic theory of superconductivity, BCS Theory, earned the scientists—John Bardeen, Leon Cooper, and John Schrieffer—the 1972 Nobel Prize in physics. A portion of the 1973 Nobel Prize in physics went to Brian Josephson, also for work with superconductivity. In January 1986, Karl Muller and Johannes Bednorz made a discovery that revolutionized how scientists thought of superconductors. Prior to this point, the understanding was that superconductivity manifested only when cooled to  near  absolute zero, but using an oxide of barium, lanthanum, and copper, they found that it became a superconductor at approximately 40 degrees Kelvin. This initiated a race to discover materials that functioned as superconductors at much higher temperatures. In the decades since, the highest temperatures that had been reached were about 133 degrees Kelvin (though you could get up to 164 degrees Kelvin if you applied a high pressure). In August 2015, a paper published in the journal Nature  reported the discovery of superconductivity at a temperature of 203 degrees Kelvin when under high pressure. Applications of Superconductors Superconductors are used in a variety of applications, but most notably within the structure of the Large Hadron Collider. The tunnels that contain the beams of charged particles are surrounded by tubes containing powerful superconductors. The supercurrents that flow through the superconductors generate an intense magnetic field, through electromagnetic induction, that can be used to accelerate and direct the team as desired. In addition, superconductors exhibit the  Meissner effect  in which they cancel all magnetic flux inside the material, becoming perfectly diamagnetic (discovered in 1933). In this case, the magnetic field lines actually travel around the cooled superconductor. It is this property of  superconductors  which is frequently used in magnetic levitation experiments, such as the quantum locking seen in quantum levitation. In other words, if  Back to the Future  style hoverboards ever become a reality. In a less mundane application, superconductors play a role in modern advancements in magnetic levitation trains, which provide a powerful possibility for high-speed public transport that is based on electricity (which can be generated using renewable energy) in contrast to non-renewable current options like airplanes, cars, and coal-powered trains. Edited by Anne Marie Helmenstine, Ph.D.