Superconductivity

Superconductivity is a special property that some materials have. In these materials, electrical resistance disappears completely, and magnetic fields are pushed away. This is very different from normal metals, where resistance slowly gets smaller as the material gets colder. Instead, a superconductor suddenly loses all resistance when it gets colder than a certain temperature, called the critical temperature.

An electric current can flow in a loop of superconducting wire forever without needing any power. This amazing phenomenon was first discovered in 1911 by a Dutch scientist named Heike Kamerlingh Onnes. It can only be explained using quantum mechanics, and it includes something called the Meissner effect, where the magnetic field inside the superconductor is completely removed when it changes into its superconducting state.

In 1986, scientists found that some special ceramic materials could become superconducting at temperatures above 35 K. By changing one of the materials, they raised this temperature to 92 K, which was important because liquid nitrogen could be used to cool these materials. Liquid nitrogen is cheap and easy to use, making experiments and applications much more practical. These materials with higher critical temperatures are called high-temperature superconductors.

History

Main article: History of superconductivity

Superconductivity was first discovered on April 8, 1911, by Heike Kamerlingh Onnes. He was studying how electricity flows through solid mercury at very cold temperatures, using liquid helium to keep things freezing. At a temperature of 4.2 K, he found that the material’s resistance suddenly dropped to zero — it could carry electricity without any loss.

In later years, scientists found superconductivity in other materials. For example, lead showed superconducting properties at 7 K, and niobium nitride at 16 K. In 1933, Meissner and Ochsenfeld discovered that superconductors push away magnetic fields, called the Meissner effect. Brothers Fritz and Heinz London explained this effect using equations that showed how superconductors behave.

In the 1950s, two big theories explained superconductivity. The Ginzburg-Landau theory described how superconductors change at certain temperatures. The BCS theory, named after Bardeen, Cooper, and Schrieffer, explained that pairs of electrons work together to create superconductivity. These ideas helped scientists understand many aspects of how superconductors work.

Classification

Main article: Superconductor classification

Superconductors are special materials that can carry electricity without any loss. They can be grouped in different ways based on how they behave.

Response to a magnetic field

A superconductor can be Type I, which means it stops working if a magnetic field gets too strong. Or it can be Type II, which allows some magnetic field to pass through in small areas called vortices when the field is between two strengths. Some materials mix these two behaviors and are called Type-1.5.

Theory of operation

Some superconductors work because of a simple interaction between electrons and vibrations in the material, explained by something called BCS theory. Others work in more complex ways and are called unconventional.

Critical temperature

Superconductors are called high-temperature if they can work at temperatures above -243°C. These can often be cooled using liquid nitrogen. Low-temperature superconductors need much colder temperatures, usually using liquid helium, to work. Some materials act like high-temperature superconductors even though their working temperature is below -243°C.

Material

Superconductors can be made from many different kinds of materials, including single elements like mercury or lead, mixtures of metals, ceramic materials, and even single layers of atoms.

Elementary properties

Superconductors are special materials where electricity can flow without any resistance. This means that if you put electricity into a loop made of superconducting wire, it can keep flowing forever without needing any more power.

When these materials get very cold, below a certain temperature, they can stop resisting electricity completely. This special temperature is called the critical temperature, and it is different for each superconducting material. Some need to be colder than -270°C to work, while others can work at warmer temperatures.

One important property of superconductors is that they can push away magnetic fields. This is called the Meissner effect. When a superconductor gets cold enough, any magnetic field around it is pushed out, except for a very thin layer right at the surface. This helps scientists understand how superconductors work and is used in important machines like those that scan the inside of the body.

High-temperature superconductivity

Superconductivity is a special property in certain materials where electricity flows without any resistance. This means that if you make a loop of this special material very cold, electricity can keep moving around it forever without needing any extra power. Normally, wires lose energy as heat when electricity flows through them, but superconductors do not. The temperature at which this happens is called the critical temperature, and below this point, the material’s resistance drops to zero instantly. This amazing property makes superconductors very useful for creating strong magnets and other advanced technology.

Applications

Main article: Technological applications of superconductivity

Superconductors are special materials that can help make new kinds of electronic devices. They can be used to create very strong magnets, which are important for machines like those used to see inside the body or to steer particles in big science experiments. These magnets can also help in separating materials or making electricity more efficient.

Superconductors have been used in computers and phone technology, and they can help make very sensitive tools to measure tiny magnetic fields. They might also help make better power grids, more efficient electric wires, and new kinds of engines for vehicles. Even though using them with alternating currents is tricky, they could make electricity transmission much better and use less space. New ways to keep these materials cold have also made using them more affordable.

Nobel Prizes

Several Nobel Prizes in Physics have been awarded for discoveries related to superconductivity.

Heike Kamerlingh Onnes won in 1913 for his work on materials at very cold temperatures. In 1972, John Bardeen, Leon N. Cooper, and J. Robert Schrieffer received the prize for creating a theory to explain superconductivity called the BCS-theory.

In 1973, Leo Esaki, Ivar Giaever, and Brian D. Josephson were honored for their experiments and theories about how electricity can move through very thin barriers in superconductors. Georg Bednorz and K. Alex Müller won in 1987 for discovering superconductivity in special ceramic materials. Finally, in 2003, Alexei A. Abrikosov, Vitaly L. Ginzburg, and Anthony J. Leggett were awarded for their important theories about superconductors and superfluids.