Physicists first received a magnetic superfluid liquid

Scientists were able to create a system that behaves like a superfluid liquid with magnetic properties. They were able to observe this in a laser trap at temperatures close to absolute zero. The results are published in the journal Physical Review Letters.

In ultracold quantum gases, particles can interact with each other in unusual modes. For example, in the framework of superfluidity. Many new properties of such objects are explained by the transition to the state of the Bose-Einstein condensate, in which many particles occupy one quantum state, due to which their behavior is very strongly correlated.

In a new work, physicists from the University of Paris-North XIII (France) cooled 40,000 chromium atoms to 400 nanokelvin to obtain a Bose-Einstein condensate. As a result, all atoms went to the lowest energy level, in which they have a nonzero magnetic spin moment. The spins of all the atoms in the rugby ball-shaped cloud of atoms were directed to one side, placing them in an external magnetic field, the strength of which gradually increased along the condensate. Because of this field, adjacent spins formed pairs, after which they tended to be directed in one direction. Then, using a radio frequency pulse, the scientists turned their backs 90 ° and began to observe the resulting dynamics.

If the magnetic field were uniform, then the spins of all atoms would begin to change direction with the same frequency and would remain parallel. In the case of an inhomogeneous field, but in the absence of pairing between the spins, they would start rotating at different frequencies, which would destroy parallelism. However, in this system with an inhomogeneous field and interaction, the spins began to oscillate around the initial positions with an amplitude depending on the position in space, while remaining substantially in the same direction.

This collective behavior of the spins corresponds to a ferromagnetic liquid, that is, to a disordered body in which strong magnetization arises in the presence of an external field. Also, this behavior can be described as a spin wave, which is observed in liquids and solids, where the close arrangement of atoms promotes the interaction between adjacent spins. However, the Bose-Einstein condensate is about 10 million times more rarefied than ordinary bodies in a condensed state. Such dynamics was observed for the first time in such a sys

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