New phase of matter discovered

Scientists have discovered a novel phase of matter characterised by an unusual ordering of electrons, that offers possibilities for new electronic device functionalities.
This phase could hold the solution to a long-standing mystery in condensed matter physics having to do with high-temperature superconductivity - the ability for some materials to conduct electricity without resistance, even at "high" temperatures approaching 100 degrees Celsius.
"The discovery of this phase was completely unexpected and not based on any prior theoretical prediction," said David Hsieh, an assistant professor at the California Institute of Technology in US.
"The whole field of electronic materials is driven by the discovery of new phases, which provide the playgrounds in which to search for new macroscopic physical properties," Hsieh said.

The researchers made the discovery while testing a laser-based measurement technique that they recently developed to look for what is called multipolar order.
In crystals with electrons moving around its interior, under certain conditions, it can be energetically favourable for electrical charges to pile up in a regular, repeating fashion inside the crystal, forming what is called a charge-ordered phase.

The building block of this type of order, namely charge, is a scalar quantity - that is, it can be described by just a numerical value, or magnitude.
In addition to charge, electrons also have a degree of freedom known as spin. When spins line up parallel to each other (in a crystal, for example), they form a ferromagnet - the type of magnet you might use on your refrigerator and that is used in the strip on your credit card.

Because spin has both a magnitude and a direction, a spin-ordered phase is described by a vector.
If the building block of the ordered phase was a pair of oppositely pointing spins - one pointing north and one pointing south - described by what is known as a magnetic quadrupole.
Such examples of multipolar-ordered phases of matter are difficult to detect using traditional experimental probes.
As it turns out, the new phase that the Hsieh group identified is precisely this type of multipolar order.
The specific compound that the researchers studied was strontium-iridium oxide (Sr2IrO4), a member of the class of synthetic compounds broadly known as iridates.

These multipolar orders might exist in many more materials, Hsieh said.
The study was published in the journal Nature Physics.