Superconductivity Temperatures Get Higher

Superconductors have the capability and the potential to revolutionize our lives through improved technology. That includes superior thermal conductivity, remarkable magnetic properties and nearly zero electrical resistance. However, all that is only possible at cryogenic temperatures, that is, at temperatures in the region of absolute zero, at -273°C or -459°F.

Researchers at the Johannes Gutenberg University Mainz and the Max Plank Institute for Chemistry are working on material, which will work as superconductors equally well at room temperature. They have developed a record high-temperature superconductor, but it smells like rotten eggs.

Although superconductors are useful in all aspects of life – from fusion reactors to MRI scanners, the major deterrent is they work below -234°C or -389°F, which rather limits their application. Although all engineers want is superconductors that work at room temperatures, until now, the best they had is cuprates or copper oxide ceramics working under normal pressures at -140°C (-220°F) or under high pressures at -109°C (-164°F).

The team led by the Max Plank Institute is using H2S or Hydrogen Sulphide as the new record-holder. Although a colorless gas, H2S is usually associated with the smell emanating from rotten eggs. The team has found that H2S, when cooled and subjected to high pressures, acts like a superconductor. The super high-pressure chamber consists of a cryogenic cell of dimensions one-cubic centimeter placed between two flat-faced diamonds.

The super-cooled liquefied hydrogen sulphide placed in the cryogenic cell is subjected to high pressure by squeezing the two diamond faces together. As the pressure reaches 1.5 megabars, the super-cooled liquid H2S becomes a superconductor. This happens at a record new high temperature of -70°C or -94°F.

Scientists placed electrodes in one of two identical cells to measure the electrical resistance and magnetic sensors in the other to measure the magnetic response of the super-cooled liquid. With this arrangement, they were able to arrive at the exact combination of pressure and temperature that caused the liquid to transition to superconductivity.

According to the team, H2S under pressure transforms to H3S, which contributes to the superconductivity. They explained the relatively high temperature of the superconductor to be mainly because of the presence of hydrogen atoms in the compound. Among all elements, hydrogen has the highest frequency of oscillations. As the gas solidifies under high pressure, it causes crystal lattices to form with strong atomic bonds in the molecule, transforming the gas to solid H3S.

The team is now setting their sights to producing superconductors with still higher transition temperatures. In their opinion, this will mean increasing the pressure to at least twice that used in their current experiment. That may also mean they will no longer be able to use H2S and instead have to use other substances such as pure hydrogen or compounds such as hydrogen rich polymers. With the latter, superconductivity may be possible at high temperatures but without the accompanying necessity for high pressure.

Head of the working group, Mikhael Eremets feels that other material may have a lot of potential for performing as conventional superconductors at high temperatures. While theoretically, there is no limit for conventional superconductors to achieve transition temperatures, the experiments conducted by the team give adequate reasons to hope that superconductivity at room temperatures can be a reality.