Unexpected properties of high-temperature superconductors

Recent discoveries of the physics of ceramic superconductors can help scientists better understand electricity without resistance.

Areas with small and isolated superconductivity exist within these substances at temperatures higher than previously known temperatures, according to a study by Princeton scientists, who have just developed the techniques. New techniques for photographing superconducting properties at the nanoscale.

Superconductivity, or the ability to carry electric current without resistance, can revolutionize the transmission of electricity if this property occurs in materials with temperatures close to normal temperatures. Even the so-called high-temperature ceramic superconductors discovered two decades ago must also be cooled to more than -100 ^° C to function.

By using a particularly suitable microscope, the Princeton team discovered that superconducting traces are still present inside this ceramic material even when they are heated to a critical temperature, in heat. how they lose their resistors. Although the experimental specimen is so hot that it cannot express superconductivity, the regions that are disconnected inside it carry Cooper pairs - pairs of electrons carrying electric current passing through the superconductor - pairs of electrons that were previously known is to appear below the critical temperature, at the temperature at which a material becomes superconducting.

Using a suitable microscope, Princeton scientists determined the power of pairs of electrons carrying currents as they formed in a ceramic superconductor.From the left side of the top, the pictures show the same 30 nanometer wide area of ​​a ceramic superconductor at a tighter turn.The red area shows the presence of superconducting pairs.Even at temperatures above the critical temperature of 10 degrees Celsius, at the temperature at which all the samples exhibit superconductivity, the pairs of electrons still exist in the left-handed regions .

These regions are only a few nanometers wide but they appear in some materials at temperatures above the critical temperature to 50 ^° C. The author of the study, Ali Yazdani, said: Understanding why these Very small areas of superconductivity exist at high temperatures - and how to create a material that expresses this property everywhere - may be a way to enhance superconductivity.

'Our measurements show that Cooper pairs exist in the inner region of the material at temperatures much higher than the critical temperature,' said Yazdani, Princeton University professor of physics. This very small area, with a special arrangement of atoms, this arrangement can cause pairs of electrons to form at very high temperatures. These regions are 'precursors' of superconductivity and are important areas to enhance superconductivity.'

For more than two decades, scientists have been working to explain and enhance the performance of ceramics based on copper oxide, ceramic substances discovered two decades ago as superconductors at a much higher temperature. Much more than other materials have been known since then - although it still requires a temperature that is standard by humans is quite cold. High-temperature superconductivity in ceramics has challenged a widely accepted explanation and is considered one of the most difficult problems in physics.

The solution of this difficult problem is to determine how electrons, negatively charged particles repel each other, change their properties to each other and form Cooper pairs in a mysterious way. Under the critical temperature, this pair forms everywhere in the material and can then act as a "superfluid" to carry the current through the material without resistance.

'In lower-temperature superconductors, electrons pair together and form a superfluid at a critical temperature,' said Yazdani. 'In ceramics, however, our team discovered that electron pairing takes place at many different temperatures and that their pairing is a very distinctive chemical activity in experimental samples, and usually in regions only a few atoms wide. '

And this very small level of research can be done thanks to the most advanced tunnel scanning microscope specifically designed by the Princeton research team to clearly see superconducting superconducting properties. while they change the temperature. The team also systematically applied its technique to a large number of high quality copper oxide superconducting samples.

Unlike optical microscopes, microscopes that use light to magnify, tunnel scanning microscopes use an electron beam from a tip to photograph a research specimen. This ray serves two purposes of the experiment: It not only provides an image of the specimen at a level of only a few atoms wide, but it also has the ability to separate pairs of electrons if it has enough energy. . By changing the energy of the electron beam, the team was able to determine whether the pair formed earlier in a predetermined place in the material.

'It took us two and a half years to observe different specimens at different temperatures to decipher this story,' said Yazdani. 'We are motivated to seek high-temperature pairing thanks to the work of others, especially the research of my colleague, Phuan Ong.'

The researchers hope to use these experimental results to clarify what controls the temperature at the atomic-level pairing in ceramic superconductors, and also to determine what makes the world the ability to coordinate together to create superconductivity of Cooper pairs.

'This type of precision experiment takes place while changing the temperature, giving us a new perspective on the complex problem of ceramic superconductors,' said Yazdani. 'If we can understand the details of what's going on in the areas inside these samples, we will be able to create a material that is more efficient overall.'

Physicist Mike Norman, a non-participant in the study, argued that such an achievement could revolutionize technology in the electric industry.

'If we can increase the critical temperature by making the sample of the study material more homogeneous, then the application of superconductivity to everyday use technologies like electrical systems will become much more practical. , Mr. Norman said. 'A good thing about superconductors is that there is no energy loss, so they can be the main players in' green 'and' effective 'technologies for energy transmission.'

Thanh Van