*Excitation of a spin liquid on a honeycomb lattice with
neutrons*
An international team of researchers, including
physicists from the University of Cambridge, have finally managed to observe a
"fingerprint" of a new state of matter that was predicted 40 years
ago but had never been observed. This new state of matter, known as
quantum spin liquid, is a state of matter in which electrons break apart.
This contradicts our current knowledge of our fundamental electron building
block, thought to be indivisible.
The article, from the University of Cambridge,
defines quantum spin liquids to be an unexplained state that has never been
conclusively observed up to this point. This was due to a thought for this
state being present in only specific magnetic materials. Researchers first came
across measurements of these fractional particles in a two-dimensional
graphene-like structure. Based on their experimental results, they were
successfully able to compare and match these findings with the Kitaev model,
the main model for a quantum spin liquid.
Dr. Dmitry Kovrizhin believes that this observation
is "an important step for our understanding of quantum matter."
Previously, he and his co-workers have tried to ask the question "if I
were performing experiments on a possible quantum spin liquid, what would I
observe?" It is believed that in typical metallic compounds, the electrons
behave similarly to magnets. The article explains, if one were to cool the
material to a low enough temperature, the electron's poles would spread out and
line up. Due to this alignment, experiments would yield distinct sharp lines. However,
in a quantum spin liquid, this does not occur. Regardless of how much the
material is cooled, even to absolute zero, the electrons will not align due to
quantum fluctuations. In an experiments, looking at the fractionalization in
alpha-ruthenium chloride, researchers analyzed the magnetic properties of the
powder by illuminating it it neutrons. The ripples resulted in broad humps
versus the distinct sharp lines seen with magnetic materials. This data aligned
nicely with research completed in 2014 by Dr. Knolle and his collaborators,
providing evidence of this observation of quantum spin liquid.
Source: http://www.cam.ac.uk/research/news/new-state-of-matter-detected-in-a-two-dimensional-material
Researchers have observed the ‘fingerprint’ of a mysterious new quantum state of matter in a two-dimensional material, in which electrons break apart.
Researchers have observed the ‘fingerprint’ of a mysterious new quantum state of matter in a two-dimensional material, in which electrons break apart.
It’s an important step for our understanding of quantum matter.Dmitry Kovrizhin
An international team of researchers have found evidence of a mysterious new state of matter, first predicted 40 years ago, in a real material. This state, known as a quantum spin liquid, causes electrons – thought to be indivisible building blocks of nature – to break into pieces.
The researchers, including physicists from the University of Cambridge, measured the first signatures of these fractional particles, known as Majorana fermions, in a two-dimensional material with a structure similar to graphene. Their experimental results successfully matched with one of the main theoretical models for a quantum spin liquid, known as a Kitaev model. The results are reported in the journal Nature Materials.
Quantum spin liquids are mysterious states of matter which are thought to be hiding in certain magnetic materials, but had not been conclusively sighted in nature.
The observation of one of their most intriguing properties — electron splitting, or fractionalisation — in real materials is a breakthrough. The resulting Majorana fermions may be used as building blocks of quantum computers, which would be far faster than conventional computers and would be able to perform calculations that could not be done otherwise.
“This is a new quantum state of matter, which has been predicted but hasn’t been seen before,” said Dr Johannes Knolle of Cambridge’s Cavendish Laboratory, one of the paper’s co-authors.
In a typical magnetic material, the electrons each behave like tiny bar magnets. And when a material is cooled to a low enough temperature, the ‘magnets’ will order themselves over long ranges, so that all the north magnetic poles point in the same direction, for example.
But in a material containing a spin liquid state, even if that material is cooled to absolute zero, the bar magnets would not align but form an entangled soup caused by quantum fluctuations.
“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, also from the Theory of Condensed Matter group of the 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?”
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.
“This is a new addition to a short list of known quantum states of matter,” said Knolle.
“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.”
Reference:
A. Banerjee et al. ‘Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet.’ Nature Materials (2016). DOI: 10.1038/nmat4604
The researchers, including physicists from the University of Cambridge, measured the first signatures of these fractional particles, known as Majorana fermions, in a two-dimensional material with a structure similar to graphene. Their experimental results successfully matched with one of the main theoretical models for a quantum spin liquid, known as a Kitaev model. The results are reported in the journal Nature Materials.
Quantum spin liquids are mysterious states of matter which are thought to be hiding in certain magnetic materials, but had not been conclusively sighted in nature.
The observation of one of their most intriguing properties — electron splitting, or fractionalisation — in real materials is a breakthrough. The resulting Majorana fermions may be used as building blocks of quantum computers, which would be far faster than conventional computers and would be able to perform calculations that could not be done otherwise.
“This is a new quantum state of matter, which has been predicted but hasn’t been seen before,” said Dr Johannes Knolle of Cambridge’s Cavendish Laboratory, one of the paper’s co-authors.
In a typical magnetic material, the electrons each behave like tiny bar magnets. And when a material is cooled to a low enough temperature, the ‘magnets’ will order themselves over long ranges, so that all the north magnetic poles point in the same direction, for example.
But in a material containing a spin liquid state, even if that material is cooled to absolute zero, the bar magnets would not align but form an entangled soup caused by quantum fluctuations.
“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, also from the Theory of Condensed Matter group of the 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?”
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.
“This is a new addition to a short list of known quantum states of matter,” said Knolle.
“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.”
Reference:
A. Banerjee et al. ‘Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet.’ Nature Materials (2016). DOI: 10.1038/nmat4604
I find it really interesting that electrons have the ability to break apart to form this new phase of matter. I wonder what the implications of the physics of this have to offer, as in how would this affect interactions with other phases of matter? -Joe Quinlan
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