In the studies of liquids, the ratchet effect and amplitude dependence of phase locking in a two-dimensional Frenkel-Kontorova model has been revealed by researchers in the Spallation Target Group at Institute of Modern Physics, Chinese Academy of Sciences (IMP).

The researchers have implemented the work in the GPU massive parallel computing center at IMP. Using the molecular dynamics simulations, the transport properties of the 2D model show that, besides the harmonic steps, the large half integer steps in the  longitudinal (x) direction has also clearly observed. These half integer steps are associated with the onset of positive and negative ratchet effects in the transverse (y) direction due to spatial symmetry breaking. Meanwhile, the analytical results of response function have been obtained, which is good agreement with the numerical one.

In the examination of amplitude dependence, it was found that the anomalies occur for the critical depinning force (Fc) and the harmonic steps, where the second lobe is smaller than the third one, the fourth lobe is smaller than the fifth one, and the sixth lobe is larger than the fifth one, while for the half integer steps, the maxima decrease monotonically with the amplitude. The phase difference of the oscillations for Fc and the width of harmonic steps is nearly equal, and 180 degree for Fc and the width of the half integer steps.

The work has been published in The Journal of Chemical Physics 138,034307 (2013).

Weblink: http://dx.doi.org/10.1063/1.4776226

Fig.1 The orbits of the particle for different amplitudes（Imaged by IMP）

Fig.2  The width and the critical depinning force Fc as a function of ac amplitude（Imaged by IMP）