摘要(英) |
We experimentally investigate particle micro-motion and the effective temperature in a quasi-2D dusty plasma Coulomb liquid confined in a narrow mesoscopic channel sheared by two parallel counter laser beams along the opposite boundaries. Liquid at the discrete level can be treated as a strongly coupled many-body system driven by stochastic noise. In addition, under an external shear, it deviates from equilibrium and becomes more complicate. Its micro-dynamics is an interesting and important issue in the study of complex systems and nano-science. However, it is difficult to construct the picture of the particle micro-motion due to the lack of proper direct observation tools and the complexity under the large degrees of freedom. Recently, the development of the dusty plasma liquid formed by the charged micro-meter sized particles suspended in low pressure discharges provides an inspiring experimental platform to study this issue. Due to the proper scale, the spatiotemporal evolutions of particle positions can be directly observed by optical microscope. In this work, by applying two laser shears to push the particle and using the idea of fluctuation-dissipation theorem, we investigate the shear induced micro-transport and the effective temperature:
1. The momentum transport (viscosity) is acquired from the ratio of mean velocity to the shear stress. For small shear, the system has a linear response, and the momentum loaded each region is uniformly. For large shear, the momentum transport is non-uniform due to the non-linear mutual coupling.
2. The particle transport (diffusivity) is acquired from the ratio of mean square displacement to the observation interval which indicates the strength of thermal fluctuation. Although the external shear is applied to the boundary and along the longitudinal direction, the transverse diffusivity is enhanced no matter the boundary and the center region. The momentum loaded to each region is finally converted to heat through the mutual coupling network.
3. The effective temperature of the system is estimated through the Einstein relation. It has similar physical meaning to the thermodynamics temperature, which indicates the energy contained in each mode and the energy cascading direction from low frequency to high frequency modes. |
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