MIT and Harvard researchers have studied how the initial units of magnetism, called spins (black arrows), revolve around a chain of atoms (colored spheres) and interact with other spins. The background blue (spin up) shows the real image of the spin by displaying the high contrast periodic modulation of the atoms. Credit: Courtesy of Researchers
These findings could help researchers design “spintronic” devices and the magnetic material of the novel.
A new study highlights amazing choreography in spinning molecules. A paper appears in the journal Nature, Researchers from MIT And Harvard University reveals how magnetic forces, atomic scales affect dimensions and how atoms direct their spin.
In experiments with ultracold lithium atoms, the researchers observed different ways in which the spins of atoms evolved. Tippy ballerinas return to a straight position, as if spinning atoms return to the equilibrium target in a way that depends on the magnetic forces between the individual atoms. For example, an atom can turn into equilibrium in a fairly fast, “ballistic” fashion, or in a slower, more diffuse method.
Researchers have found that these behaviors, which have not been observed recently, can be mathematically described by the Heisenberg model, a set of equations commonly used to predict magnetic behavior. Their results address the basic nature of magnetism, showing the diversity of behavior in a simple magnetic material.
This improved understanding of magnetism will help engineers create “spintronic” devices that transmit, process, and store information using the spin of quantum particles instead of the flow of electrons.
John D., a professor of physics at MIT. “By studying a simple magnetic material, we have advanced the understanding of magnetism,” says Wolfgang Ketterle, Arthur and MIT team leader. “When you see a new phenomenon in one of the simplest models of physics for magnetism, you have the opportunity to fully describe and understand it. This is what makes me get out of bed in the morning and cheers me up. “
Keater’s co-authors are Paul Nicholas Japson, a graduate student at MIT and lead author, Jesse-Amato Grill, Ivana Dimitrova, both MIT postdocks, Harvard University and Stanford University postdock van Wei Ho, and Eugene Daimler, a professor of physics. At Harvard. Is a researcher at the MIT-Harvard Center for All Ultra Old Atoms. The MIT team is affiliated with the Department of Physics and Research Laboratories of Electronics.
The stars of spin
Quantum spin is considered to be the microscopic unit of magnetism. On a quantum scale, atoms can spin clockwise or counterclockwise, giving them a compass needle-like direction. In magnetic materials, the spin equilibrium states of many atoms can show a variety of events, including where Atom Spin is aligned, and dynamic behavior, where the spin in many molecules resembles a wave-like pattern.
This is the next method that was studied by researchers. The dynamics of the wavelength spin pattern are very sensitive to the magnetic forces between the atoms. The avy wavy pattern fades much faster to isotropic magnetic forces than anisotropic forces. (Isotropic forces do not depend on how all spins are oriented in space).
Kettler’s group was to study the phenomenon with an experiment in which they used laser-cooling techniques to bring lithium molecules down to about 50 nanoclavins – more than 10 million times colder than in international space.
At such ultracold temperatures, the atom freezes near, so that researchers can see in detail any magnetic effects that are masked by the thermal motion of the atom. The researchers then used a system of lasers to trap and arrange multiple wires, like a string on a string with 40 atoms. In all, they produced about 1,000 wire mesh, containing about 40,000 atoms.
“You can think of a laser as a tweezer that catches atoms, and if they’re hot they escape,” Japson explains.
They then applied a pattern of radio waves and a pulsed magnetic force across the lattice, which induced each atom to turn its spin into a helical (or wavelike) pattern. These wave-like patterns of wire simultaneously correspond to the periodic density modulation of the “spin up” molecule that forms a pattern of stripes, which researchers can image on a detector. They then observed how the striped patterns disappeared as the individual spins of the atoms approached their equilibrium state.
Kettle compares the experiment to putting a guitar string. If researchers look at the spin of equilibrium atoms, this will not tell them much about the magnetic forces between the atoms, as the rest of the guitar strings will not reveal much about its physical properties. By lengthening a string, bringing it out of balance, and seeing how it vibrates and finally returns to its original position, one can learn something basic about the physical properties of a string.
“What we’re doing here is, we’re putting the words of the spin. We are putting this helix pattern, and then observing how this pattern behaves as a function of time, ”says Kettle. “This allows us to see the effect of different magnetic forces between spins.”
Ballistics and ink
In their experiment, the researchers modified the force of the applied pulse magnetic force to change the width of the stripes of the atomic spin pattern. They measured how quickly, and how, the patterns diminished. Depending on the nature of the magnetic forces between the atoms, they observed surprisingly different behaviors in how quantum spins returned to equilibrium.
They found a transition between ballistic behavior, where the spin quickly turned to equilibrium, and dissipated behavior, where the spin spreads more irregularly, and the overall striped pattern gradually spreads toward equilibrium, as ink drops slowly dissolve in water. Is.
Some of these behaviors have been theoretically predicted, but have never been seen in detail to date. Some other results were completely unpredictable. What’s more, the researchers found that their observations mathematically fit from the calculations they made with the Heisenberg model for their experimental parameters. He joined Harvard theorists, who performed advanced calculations of spin dynamics.
“It was interesting to see that there were properties that were easy to measure, but difficult to calculate, and other properties could be calculated, but not measured,” says Ho.
In addition to advancing the understanding of magnetism at the basic level, the team’s results can be used as a type of quantum simulator, to explore the properties of new materials. Such platforms can function like a special-purpose quantum computer that calculates the behavior of content, in a way that exceeds the capabilities of today’s most powerful computers.
“With all the current thrills about the promise of quantum information science to solve experimental problems in the future, it’s great to see a fruit like this today,” says John Gillespie, program officer in the Division of Physics. National Science Foundation, a fund for research.
References: Paul Nicklaus Japson, Jesse Amato-Grill, Ivana Dimitrova, Van Wei Ho, Eugene Daimler and Wolfgang Ketterle, 16 December 2020, “Spin transfer in a Heisenberg model compatible with allotracold atoms” Nature.
DOI: 10.1038 / s41586-020-3033-y
The research was also supported by the Department of Defense and the Gordon and Betty Moore Foundation.
