An international team of researchers - including physicists from the University of Cambridge - has discovered a new state of matter that was predicted 40 years ago. The mysterious state, known as a quantum spin liquid, causes electrons to break into pieces and could help scientists get closer to creating a quantum computer.
Although scientists have long hypothesized that quantum spin liquids hide in certain magnetic materials, these mysterious states of matter have not been observed in nature until now. The new observation of one of their most unique properties, electron splitting, is a breakthrough in the field.
The international team measured the first signatures of these unique fractional particles - Majorana fermions - in a two-dimensional material that possessed a similar structure to graphene. The results matched up with the main theoretical model for a quantum spin liquid, the Kitaev model.
After electron splitting occurs in quantum spin liquids, the resulting Majorana fermions can be used the create quantum computers that could perform calculations not possible in standard computers.
"This is a new quantum state of matter, which has been predicted but hasn't been seen before," said Johannes Knolle, co-author of the study and a member of Cambridge University's Cavendish Laboratory.
In standard magnetic materials, electrons behave like small bar magnets. At lower temperatures, these magnets order themselves. For example, at times they will align all of the north magnetic poles in the same direction.
Conversely, materials that contain spin liquid states do not align even at the lowest temperatures, instead forming a web that is caused by quantum fluctuations.
"Until recently, we didn't even know what the experimental fingerprints of a quantum spin liquid would look like," said Dmitry Kovrizhin, co-author of the paper and also from 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?"
The team used neutron scattering techniques to examine electron splitting in crystals of ruthenium chloride (RuCl3), testing the magnetic properties of the crystals by using neutrons to illuminate them in order to observe the resulting pattern of ripples.
The resulting electron splitting patterns matched with what was predicted by the Kitaev model, providing the first direct evidence of a quantum spin liquid state of matter, as well as electron splitting, in a two dimensional material.
"This is a new addition to a short list of known quantum states of matter," Knolle said.
"It's an important step for our understanding of quantum matter," Kovrizhin added. "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."
The findings were published in the April 4 issue of Nature Materials.
