When does superconductivity occur at room temperature?

The dream of the superconductor

Another physics dream seems to be coming true. A superconductor that shows conductivity at relatively high temperatures and is inexpensive and easy to manufacture was presented a few days ago at a conference in Seattle.

Excitement in Seattle

As the latest edition of "Nature" reports, there was excitement at the short-term conference on superconductors in Seattle, USA.

The superconductor magnesium diboride (MgB2) was the focus of physical interest. Briefly presented for the first time in Tokyo by Jun Akimitsu from "Aoyoma Gakuin University", the superconductor should lose its entire electrical resistance at 39 degrees Kelvin (corresponds to approx. - 234 degrees Celsius) and become superconducting. According to the enthusiastic physicists, the component is inexpensive and relatively easy to manufacture.

First metallic superconductors

The earliest superconductors were metallic, but required cumbersome and expensive equipment to cool them down to a temperature just above absolute zero (zero degrees Kelvin, -273.15 degrees Celsius). That changed in 1986 after the discovery of the superconductivity of copper oxides at 90 degrees Kelvin.

Simple metallic superconductors were forgotten during the search for superconductors in the high temperature range. With the comprehensive presentation of the magnesium diboride superconductor in Seattle, they moved back to the center of attention.

Superconductivity

In 1911 H. Kamerlingh Onnes discovered the property of some metals and alloys to no longer offer any resistance to the electric current in the vicinity of absolute temperature zero. The transition from the normal to the superconducting state takes place very suddenly at a transition temperature that is determined for each substance (up to the discovery of the high-temperature superconductors in 1986 below 23.3 Kelvin, then up to 133.5 Kelvin). During this transition, other physical, e.g. B. the magnetic properties in an unusual way.

More about high temperature superconductors

Surprising behavior

MgB2 behaves like a conventional metallic low-temperature superconductor - except for the fact that it conducts at higher temperatures, to the great amazement of the physicists in Seattle.

There have been several attempts to improve the performance of MgB2 to increase. A research group led by Bob Cava from Princeton University tried individual magnesium atoms in MgB2 to be replaced by aluminum, which led to a destruction of the superconductivity. According to some scientists, the solution to this problem could not consist in replacing individual atoms, but in adding more elements.

First indications of applicability

At the recent conference in Seattle, different groups of scientists described how MgB2 can be integrated into cables and thin films, as the first steps towards applicable technologies, so to speak.

As an example, physicists from Iowa State University presented a simple way to manufacture superconducting lines: They exposed commercial boron fibers to a temperature of 950 Kelvin magnesium vapor. The Iowa state physicists believe that they can produce superconducting magnets or similar applications in this way.

Organic molecules as superconductors

The synthesis of organic macromolecules, which are still superconducting at room temperature, does not seem to be ruled out. According to the BCS theory (by J. Bardeen, L. Cooper and J. R. Schrieffer), two conduction electrons of a metal form what are known as Cooper pairs below a certain low temperature. These electron pairs can move freely through the metal lattice, i.e. H. the electrical resistance disappears. If the temperature rises, the pairs are separated again. The individual electrons have become normal conduction electrons; the electrical resistance occurs again. The BCS theory explains many properties of superconductors. B. find more and more use in particle accelerators.

Powerful alternative?

What can make MgB2 a real alternative to copper oxide superconductors in the future are not only the moderate "operating temperatures" of the material, but also the low manufacturing costs.

The future will tell whether the enthusiasm sparked in Seattle can now be converted into competitive applications and products. There is a lot to be said for it.

The latest results on the subject can be found in the Los Alamos archive.

Los Alamos Archives

Superconductivity Group Home Page

Department of Physics at Princeton University

A new generation of effective superconductors?

According to Japanese scientists from the University of Tokyo, a new material called magnesium diboride should enable innovative superconducting technologies in the future.

Superconductors lose their resistance to electrical current below a critical temperature. Jun Akimitsu and his colleagues have now found magnesium boride (MgB2) a substance that develops superconductivity at minus 234 degrees Celsius. This represents a significant advance compared to currently available components.

Superconducting materials

In 1911 H. Kamerlingh Onnes discovered the property of some metals (lead, mercury) and alloys (collectively called superconductors) to no longer offer any resistance to the electric current near absolute zero. If, for example, a current is induced in a superconducting wire loop, it will flow for many hours after the primary circuit has been switched off. The transition from the normal to the superconducting state occurs very suddenly at a certain transition temperature for each substance (up to the discovery of high-temperature superconductors in 1986 below 23.3 K, then up to 133.5 K). During this transition, other physical, e.g. B. the magnetic properties in an unusual way.

More about superconductors

Small cause - big effect

Past experiments have shown that a slight change in the construction of superconducting materials can have significant effects on the temperature threshold for superconductivity.

The new substance magnesium boride (MgB2) promises new generations of superconductors that can also be used economically, according to scientists at Tokyo University.

Use in particle accelerators

The synthesis of organic macromolecules, which are still superconducting at room temperature, does not seem to be ruled out. According to the BCS theory (developed by J. Bardeen, L. Cooper and J. R. Schrieffer in 1957; Nobel Prize in Physics 1972), two conduction electrons of a metal form so-called Cooper pairs below a certain low temperature. These electron pairs can move freely through the metal lattice, i.e. that is, the electrical resistance disappears. If the temperature rises, the pairs are separated again. The individual electrons have become normal conduction electrons; the electrical resistance occurs again. The BCS theory explains many properties of superconductors that are used more and more (e.g. in large computer systems and particle accelerators).

More about high temperature superconductors

"There is a great chance that superconducting components made of magnesium boride can display specific current-conducting properties," said Bob Cava of Princeton University about the prospects for the new superconductor in Nature Magazine.

University of Tokyo

Princeton University