A new ordered phase of matter has been discovered by Caltech researchers, which has big implications for superconductors – materials that conduct electricity with no resistance. The team thinks that this phase happens just before a material turns superconductive. Scientists are interested in superconductors as they transmit electricity and signals without losing energy.
Two phases (not to be confused with states) of matter had been observed in materials so far, which describe how electrons are distributed within the material. The first one is called charge-ordered phase and requires a regular accumulation of electrons inside a crystal. Electrons in charge-ordered phase materials are spread out in specific and repeating patterns which correspond with the most energetically favorable distribution.
Electrons have a property called spin. In very simplistic (and not entirely accurate) terms, you can imagine the electrons as tiny spinning tops, and the direction in which the tops point is the direction of the spin. In most materials, they have random direction. If they are all parallel to each other the material is magnetic and known as spin-ordered phase. Such materials are used in a wide range of products, from fridge magnets to credit cards.
The new ordered phase detected correspond to having pairs of electrons pointing their spin in opposite directions. The phase is called multipolar-ordered phase.
The team discovered this phase in a specific iridate compound called strontium-iridium oxide (Sr2IrO4). This compound is interesting as it shares many properties with cuprates, materials that exhibit superconductivity at (relatively) high temperatures (over -173 °C ,-279.4 °F). Normally, materials have to be cooled to close to absolute zero to become superconductive, limiting their use and applications.
To make cuprates superconductive, it’s necessary to “dope” them by adding or removing electrons, changing the material from an insulator to an ideal conductor. Before becoming a superconductor, cuprates go through a mysterious phase called "pseudogap." Sr2IrO4 displays a similar pseudogap and the new phase of matter discovered by Hsieh’s group exists over the same doping and temperature range, hence suggesting a link to superconductors.
"There is also very recent work by other groups showing signatures of superconductivity in Sr2IrO4 of the same variety as that found in cuprates," Hsieh said in a statement. "Given the highly similar phenomenology of the iridates and cuprates, perhaps iridates will help us resolve some of the longstanding debates about the relationship between the pseudogap and high-temperature superconductivity.
Hsieh believes this ordered-phase might not be rare at all. "Sr2IrO4 is the first thing we looked at, so these orders could very well be lurking in other materials as well, and that's exactly what we are pursuing next."
The research is published in the November issue of Nature Physics.