February 28, 2023 feature
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Observing phononic skyrmions based on the hybrid spin of elastic waves
Skyrmions are extremely small with diameters in the nanoscale, and they behave as particles suited for information storage and logic technologies. In 1961, Tony Skyrme formulated a manifestation of the first topological defect to model a particle and coined it as skyrmions. Such particles with topologically stable configurations can launch a promising route toward establishing high-density magnetic and phononic (a discrete unit of quantum vibrational mechanical energy) information processing routes.
In a new report published in Science Advances, Liyun Cao and a team of researchers at the University of Lorraine CNRS, France, experimentally developed phononic skyrmions as new topological structures by using the three-dimensional (3D) hybrid spin of elastic waves. The researchers observed the frequency-independent spin configurations and their progression toward the formation of ultra-broadband phononic skyrmions that could be produced on any solid structure.
The new research work opens a vibrant horizon to regulate elastic waves and structures based on spin configuration, thus offering alternative phononic technologies well suited for information processing, biomedical testing and wave engineering applications.
The physics of skyrmions
Skyrmions can be defined as a topologically stable three-component vector-field, as demonstrated in condensed matter systems and helimagnetic materials. Such phenomena form promising avenues for information storage and transfer. Physicists are exploring nontrivial skyrmion configurations for elastic phonons known as "elastic waves in solids" due to their sophisticated polarization states. When compared with photonic systems, elastic phonons provide an excellent platform to carry and process information due to their unique features, which include a scalability towards forming integrated devices and an anti-jamming capacity with extremely low losses.
Phonon physics has led to advanced technologies in high signal-to-noise information processing, alongside intense wave-matter interactions suited for quantum networks. In this new work, Cao and colleagues have developed a nontrivial topological structure of ultrabroadband phononic skyrmion-based on the 3D hybrid spin of elastic waves. The team formed the phononic and photonic skyrmions via different spin textures.
Forming phononic skyrmions via intrinsic hybrid spins
Researchers can establish elastic spin by hybridizing transverse and longitudinal waves in an elastic interface. This hybrid spin can be formed on a free surface that supports Lamb waves and Rayleigh waves and also exist in an infinite isotropic bulk space without interfaces based on two-wave interference.
The researchers created a compact structure by building the phononic skyrmion system within a thin-plate model that supported the hybrid spin of the Lamb wave that arose from the hybridization between longitudinal and transverse waves in the upper and lower plate interfaces of the experimental setup. In order to create the phononic skyrmions in the lab, the team designed a hexagonal metaplate with pillared resonators and excited three pairs of counter-propagating plane Lamb waves with hybrid spins during the experiment.
Tunable characteristics of the elastic, robust phononic skyrmions
Cao and colleagues observed the ultra-broadband topological robustness feature of the phononic skyrmions caused by the frequency-independent 3D hybrid spin texture of the elastic waves. They also facilitated fluid-solid coupling to develop a non-trivial acoustic skyrmion field in fluids. The team then used a 3D printer to print a hexagonal-symmetry metaplate with pillared resonators and noted good agreement between the experimental and simulated dispersions. They then confirmed broadband characteristics of the phononic skyrmions and observed transitions of different types of skyrmions in the geometric space, which showed the contribution of pillared resonators towards constructing 3D skyrmion configurations.
The work additionally established the robustness of the nontrivial topological phononic skyrmion lattices. For instance, when the team introduced defects to the setup, they did not affect the skyrmion lattice architecture, proving that phononic skyrmions were robust against the defects, indicating stability of the skyrmion field.
Outlook
In this way, Liyun Cao and colleagues described and observed the formation of ultra-broadband phononic skyrmions in theory and in practice based on the 3D hybrid spin of elastic waves. The phononic skyrmions were robust against local defects of disorder, and demonstrated ultra-bandwidth, well-suited for high-speed topological phononic information processing technologies. The 3D hybrid spin states can open new pathways to regulate phonons and explore new topological orders.
The work presents a range of possibilities to create new topological phononic materials across the macro-to-microscale. The scientists showed the possibility of creating tunable, phononic skyrmions in any elastic wave system, including solid-solid, solid-gas or solid-liquid interfaces. Of note, the fluid-solid coupling can pave the way toward skyrmion lattice matter systems in fluids, well suited to observe cell dynamics in microfluidics instruments and for biomedical testing. These outcomes will facilitate advanced integrated information platforms to connect interdisciplinary physics across electronics, phononics/photonics and the life sciences.
More information: Liyun Cao et al, Observation of phononic skyrmions based on hybrid spin of elastic waves, Science Advances (2023). DOI: 10.1126/sciadv.adf3652
Shujie Yang et al, Harmonic acoustics for dynamic and selective particle manipulation, Nature Materials (2022). DOI: 10.1038/s41563-022-01210-8
Journal information: Nature Materials , Science Advances
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