Scientists Discover the ‘Fingerprint’ of a Mysterious New Quantum State of Matter

Solid. Liquid. Gas. Plasma and a dozen or so other states.  And now… Quantum spin liquid, a state that causes electrons (once, when some of us were still in high school, believed to be one of the basic indivisible building blocks of matter) to break into its constituent quasiparticles, called Majorana fermions. Quantum spin liquid technically is not a liquid, just as plasma isn’t technically a gas.

Scientists Discover the ‘Fingerprint’ of a Mysterious New Quantum State of Matter

This is how they did their experiment, according to the University of Cambridge:

About four decades ago physicists first predicted the state would occur in certain magnetic materials. An international team of physicists, including some from the University of Cambridge, have published a paper in Nature Materials detailing their discovery.

What are the characteristics of a quantum spin liquid? Well, electrons in a magnetic field will tend to align themselves in a single direction as the temperature of a magnetic material approaches absolute zero.

A material that contains a spin liquid state breaks this rule because the electrons would not align at absolute zero, and instead form a complicated mess because of quantum fluctuations.

The researchers detected the first signatures of Majorana fermions in a two-dimensional graphene-like material, matching the Kitaev model of quantum spin liquid.

Knolle and Kovrizhin’s co-authors, led by Dr Arnab Banerjee and Dr Stephen Nagler from Oak Ridge National Laboratory in the US, used neutron scattering techniques to look for experimental evidence of fractionalisation in alpha-ruthenium chloride (α-RuCl3). The researchers tested the magnetic properties of α-RuCl3 powder by illuminating it with neutrons, and observing the pattern of ripples that the neutrons produced on a screen when they scattered from the sample.

A regular magnet would create distinct sharp lines, but it was a mystery what sort of pattern the Majorana fermions in a quantum spin liquid would make. The theoretical prediction of distinct signatures by Knolle and his collaborators in 2014 match well with the broad humps instead of sharp lines which experimentalists observed on the screen, providing for the first time direct evidence of a quantum spin liquid and the fractionalisation of electrons in a two dimensional material. 

Basically, researchers bombarded a powdered material with neutrons. The neutrons would bounce off of the material and scatter onto a screen where they would be recorded, with a pattern of sharp lines associated with normal stuff and broad humps predicted for quantum spin liquid. (disclaimer: the author does not have a PhD in neurophysiochemigastonomy )

“This is a new quantum state of matter, which has been predicted but hasn’t been seen before,” said one of the paper’s co-authors, Dr Johannes Knolle from Cavendish Laboratory, Cambridge.

“This is a new addition to a short list of known quantum states of matter,” he said.

“Until recently, we didn’t even know what the experimental fingerprints of a quantum spin liquid would look like,” said paper co-author Dr Dmitry Kovrizhin from Cavendish Laboratory. “One thing we’ve done in previous work is to ask, if I were performing experiments on a possible quantum spin liquid, what would I observe?”

“It’s an important step for our understanding of quantum matter,” said Kovrizhin. “It’s fun to have another new quantum state that we’ve never seen before – it presents us with new possibilities to try new things.”

Yes. Fun.

Sources: Nature Materials Phys.Org Gizmondo Science Alert Cambridge University



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