Four decades after it was first predicted to exist, evidence of a new state of matter known as a quantum spin liquid has been discovered in an actual material, physicists from the University of Cambridge and their colleagues reported Monday in the journal Nature Materials.
Quantum spin liquids have long been thought to cause electrons, the invisible building blocks of nature, to become fragmented, the researchers explained in a statement. Now, the first signatures of the mysterious particles created by this process (also known as Majorana fermions) have been detected in a series of experiments involving a two-dimensional, graphene-like material.
The results of these experiments were a close match to one of the primary theoretical models for a quantum spin liquid – a model known as a Kitaev model. While researchers have predicted that this state of matter was present in some magnetic materials, it had not been conclusively spotted in nature, and the discovery could greatly benefit the development of quantum computers.
“This is a new quantum state of matter, which has been predicted but hasn’t been seen before,” co-author Dr. Johannes Knolle from the Theory of Condensed Matter group at the university’s Cavendish Laboratory, explained in a statement. “This is a new addition to a short list of known quantum states of matter.”
‘Important step forward’ in the field of quantum computing
Now that Dr. Knolle and his colleagues have observed the phenomenon of fractionalization (or electron splitting), there is a possibility that the Majorana fermions produced as a result of this process could be used as the foundation of quantum computing technology that would be much faster and capable of completing calculations beyond the scope of conventional systems.
In most magnetic materials, the electrons behave in a manner similar to regular bar magnets, the study authors explained. When a material is cooled to a low-enough temperature, the electrons in the magnets order themselves so that all of the similar poles point in the same direction. In those containing a spin liquid state, however, the magnets do not align. Instead, they become entangled due to quantum fluctuations.
“Until recently,” said co-author Dr. Dmitry Kovrizhin, also at the Cavendish Laboratory, “we didn’t even know what the experimental fingerprints of a quantum spin liquid would look like. 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?”
The Cambridge researchers, along with colleagues from the Oak Ridge National Laboratory in Tennessee, used neutron scattering techniques to search for signs of electron splitting in crystals of ruthenium chloride (RuCl3). They illuminated the RuC13 crystals with neutrons to test their magnetic properties, and found signatures matching the theoretical Kitaev model.
Their research provides the first direct evidence of a quantum spin liquid and electron splitting in a two-dimensional material – a breakthrough that Dr. Kovrizhin called “an important step for our understanding of quantum matter.” He added that it was “fun to have another new quantum state that we’ve never seen before – it presents us with new possibilities to try new things.”
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Image credit: Genevieve Martin, Oak Ridge National Laboratory
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