The tiny YbMgGaO4 crystal, here perched on a stand for testing, appears to be the next extremely rare material to produce an equally as rare observable quantum spin liquid. Credit: Georgia Tech / Martin Mourigal
Inside a new exotic crystal, physicist Martin Mourigal has observed strong indications of “spooky” action, and lots of it. The results of his experiments, if corroborated over time, would mean that the type of crystal is a rare new material that can produce an observable quantum spin liquid. Currently, only a small handful of materials are believed to possibly have these properties. This new crystal was synthesized for the first time only a year ago.
A “liquid” found inside a solid object may sound confusing to many people. The workings of computers, cell phones, superconductors and MRI machines are based on quantum materials. Quantum entanglement has since been proven in experiments, but now scientists like Mourigal, an experimental physicist at the Georgia Institute of Technology, and his team, have taken it much farther. The synthetic crystal he has examined, an ytterbium compound with the formula YbMgGaO4, is likely brimming with observable ‘spooky’ connections.
This massive “spooky” entanglement makes a system of electrons a quantum spin “liquid”~ here, it describes the collective nature of electrons’ spins in the crystal. “In a spin ‘liquid,’ the directions of the spins are not tidily aligned, but frenzied, although the spins are interconnected, whereas in a spin ‘solid’ the spin directions have a neat organization,” Mourigal said. If the discovery stands, it could open a door to hundreds of yet unknown quantum spin liquid materials that must exist according to theory and mathematical equations. In the future, new quantum materials could become a virtual sorcerer’s stones in quantum computing engineers’ hands.
The ytterbium crystal was first synthesized a year ago by scientists in China, where the government in Beijing has invested heavily in hopes of creating synthetic quantum materials with novel properties. It appears they may have now succeeded, said Mourigal, an assistant professor at Georgia Tech’s School of Physics. “Imagine a state of matter where this entanglement doesn’t involve 2 electrons but involves, 3, 5, 10 or 10 billion particles all in the same system,” Mourigal said. “You can create a very, very exotic state of matter based on the fact that all these particles are entangled with each other. There are no individual particles anymore, but one huge electron ensemble acting collectively.”
A massive part of Oak Ridge National Laboratory’s Spallation Neutron Source during its construction phase in earlier years. The hole in the center is where the target crystal for neutron scattering is placed. Credit: Oak Ridge National Laboratory
One of the only previously observed apparent quantum spin liquids occurs in a natural crystal herbertsmithite, an emerald green stone found in 1972 in a mine in Chile. It was named after mineralogist Herbert Smith, who died nearly 20 years prior to the discovery. Researchers confirmed its spin liquid nature in 2012 after MIT scientists succeeded at reproducing a purified piece of the crystal in their lab. Because of its chemical makeup, herbertsmithite produces just one single entanglement scheme. Physics math says there must be myriads more. “It’s important to create the encyclopedia of them,” Mourigal said. “This new crystal may be only our second or third entry.”
Physicists from the University of Tennessee succeeded in replicating the original ytterbium crystal, and Mourigal examined it at Oak Ridge National Laboratory (ORNL), where it was cooled down to a temperature of -273.09 degrees Celsius (0.06 Kelvin). The cooling slowed the natural motion of the atoms to a near stop, which allowed them to observe electron spins’ dance around the Ytterbium (Yb) atoms in the YbMgGaO4 crystal. They used a powerful superconducting magnet to line the spins up in an orderly fashion to create a starting point for their observations. “Then we removed the magnetic field, and let them go back to their special kind of wiggling,” Mourigal said. The scientists to watch the concert of electrons’ spins by bombarding them with neutrons.
Normally, when one electron flips its spin, researchers would expect it to create a neat chain reaction, resulting in a wave going through the crystal. But something odd happened. “This jumbly kind of spin wave broke down into many other waves, because everything is collective, everything is entangled,” Mourigal said. “It was a continuum of excitations, but breaking down across many electrons at once.”
It was qualitatively similar to what was observed using the same technique on herbertsmithite. To authenticate the observations made by Mourigal’s team, theoretical physicists will have to crunch the data with methods that, in part, rely on topology. Mourigal thinks chances are they will pass muster. “At first glance, this material is screaming, ‘I’m a quantum spin liquid,'” he said. But it must undergo a years-long battery of stringent mathematical tests. The theoretical physicists will wrap the data around a mathematical “donut” to confirm it is a quantum spin liquid. Mourigal said. “As a mathematical mental exercise, they virtually spread the spin liquid around a donut shape, and the way it responds to being on a donut tells you something about the nature of that spin liquid.”
Though entangled particles appear to defy space and time, the shape of space they occupy affects the nature of the entanglement pattern. The possibility of a quantum spin liquid was first demonstrated in the 1930s, but only using atoms placed in a straight line. Physicists have been searching in the decades since for materials containing them. http://www.rh.gatech.edu/news/584639/spooky-sightings-crystal-point-extremely-rare-quantum-spin-liquid
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