Skyrmions are topologically stable quasiparticles that can form in a vector field, such as the spin texture of a magnetic material. As such, conventional wisdom suggests that skyrmions should not appear in acoustic waves, which are spinless scalar waves. Now, Ming-Hui Lu of Nanjing University in China and colleagues have created acoustic skyrmions using an acoustic metasurface and an array of loudspeakers [1]. The result extends the range of media known to sustain skyrmions and could lead to new ways of manipulating microscopic objects.
The key to the new result is a property of acoustic waves that the researchers say is often overlooked: Although the density oscillations that constitute these waves have no intrinsic orientation themselves, they are accompanied by coherent motion of the local acoustic medium. It is in this 3D velocity field that the team formed their acoustic skyrmions.
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