Ultra-fast laser pulses unlock ‘quite unusual’, unseen phase of matter

12 Nov 2019

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Researchers have used powerful lasers to reveal a new phase of matter that could unlock undiscovered properties in materials of all kinds.

When energy is added to any material, its structure typically becomes less orderly. For example, adding heat to ice will melt its structure, resulting in liquid water.

However, physicists at MIT have reported in Nature Physics the discovery of a new, previously unseen phase of matter where the opposite is true. They showed that when a pattern called a charge density wave (CDW) in a particular material is hit with an ultra-fast laser pulse, a highly ordered state is created.

This surprising discovery, they said, could help us find ways of unlocking previously unknown properties in materials of all kinds. The material used in the experiments was lanthanum tritelluride, which naturally forms itself into a layered structure.

Within the material, the CDWs of electrons form spontaneously and are confined to a single direction. But when it’s hit with a laser burst for less one picosecond, the CDW is obliterated and a new one forms at right angles to the original.

This phenomenon has never been seen in the material, existing for only a matter of picoseconds. The fact that the original one comes back into view, the researchers said, suggests that its presence is somehow suppressed by the original CDW.

Potential for superconductors

“This is quite unusual. In most cases, when you add energy to a material, you reduce order,” said Anshul Kogar, a postdoc researcher of the study.

“It’s as if these two [kinds of CDW] are competing — when one shows up, the other goes away. I think the really important concept here is phase competition.”

Given the fact that two states of matter might be in competition, with one dominating the other, is fairly common in quantum materials, the researchers said that this discovery could show that there may be latent states lurking in many kinds of matter. They just need to be unlocked somehow.

Nuh Gedik, another researcher, said: “By knocking out that dominant state with light, maybe those other states can be realised. What if all you need to do is shine light on a material, and this new state comes into being?” he added.

These findings could answer why superconductivity occurs at high temperatures in certain materials, potentially opening the door to future superconductors that don’t need to operate at freezing temperatures.

Colm Gorey was a senior journalist with Silicon Republic