| dc.description.abstract | Wave vortices (WV), as coherent entities, have been widely observed in various wave systems, such as optical, acoustic, elastic, water surface, quantum-fluid and atom waves. They are characterized by helical wave fronts winding around screw dislocation filaments with undefined phases and null amplitudes. Previous studies have demonstrated the generation of WVs in linear wave media through the superposition of single-scale plane waves with different propagation directions or the same propagation direction with different phases. In nonlinear wave media, modulation instability induces waveform undulations, leading to pair generation of WVs and multiscale WVs in weakly disordered waves and wave turbulence, respectively. However, whether multiscale WVs exist and how multiscale WVs can be generated in the linear disordered multiscale wave system remains open question.
Down to the microscopic level, the competition between mutual interactions among particles and thermal agitations excites multiscale disordered phonons with various propagation directions in cold crystals. In cold solids far from the melting transition, thermally excited small-amplitude phonons do not interact with each other, making harmonic crystals excellent examples for exploring multiscale spatiotemporal waveform dynamics and testing whether WVs act as coherent entities in linear disordered multiscale wave system.
In this work, employing empirical mode decomposition, we experimentally and numerically demonstrate the observations of multiscale acoustic vorticity waves and vorticity wave vortices as multiscale coherent entities in thermally driven disordered vibrations of two-dimensional dusty plasma and Yukawa crystals under low viscous damping. In each low-frequency mode, the vorticity waves appear in the form of irregular vortex arrays with spatiotemporally varying vortex shapes and vorticities, predominately contributed by transverse phonons. These disordered waves can be viewed as a collection of localized coherent entities of multiscale vorticity wave vortices with vorticity wave crests winding around worm-like screw-dislocation filaments in the xyt space, exhibiting stretched-exponential lifetime distribution and short-range spatial correlations. These findings provide insights into the complex dynamics of disordered linear wave systems and offers a novel framework to study disordered waves in various media for advances in condensed matter physics and material science. | en_US |