Department of Physics, Tokyo Institute of Technology1
When a periodic shear is applied to many-particle assemblies with disordered configuration, the particles gradually self-organize to avoid future collisions and transform into an organized configuration. For a small shear amplitude d, the particles finally settle into a reversible state where all the particles return to their initial position after each shear cycle, while they reach an irreversible state for d above a threshold amplitude dc [1]. Using periodically sheared vortices in amorphous MoxGe1-x films with random pinning, we have demonstrated the critical behavior of the reversible-irreversible transition (RIT) or irreversibility transition. The relaxation time to reach the steady state, plotted against d, shows a power-law divergence at dc, indicative of a nonequilibrium RIT [2,3]. The critical exponent agrees with the value expected for an absorbing phase transition in the two-dimensional directed-percolation universality class [4,5]. In previous experiments, RIT was induced by increasing d at a fixed vortex density n (i.e., fixed field B). This situation is qualitatively equivalent to the one where n (i.e., B) is increased at fixed d. However, it is not evident whether the same critical behavior is observed irrespective of the parameters. In colloidal suspensions, RIT was observed in different regimes of n [6], but it is difficult to conduct an experiment where n is systematically changed at fixed d. Here, we perform such an experiment using the vortex system and find that the same critical behaviors of RIT are observed irrespective of the control parameters (d or n). The results further demonstrate the universality of RIT.
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[2] S. Okuma, Y. Tsugawa, and A. Motohashi, Phys. Rev. B 83, 012503 (2011).
[3] M. Dobroka et al., New J. Phys. 19, 053023 (2017).
[4] S. Maegochi, K. Ienaga, S. Kaneko, and S. Okuma, Sci. Rep. 9, 16447 (2019).
[5] H. Hinrichsen, Adv. Phys. 49, 815 (2000).
[6] N. C. Keim and P. E. Arratia, Phys. Rev. Lett. 112, 028302 (2014): K. H. Nagamanasa et al., Phys Rev E 89, 062308 (2014).
Keywords: nonequilibrium transition, dynamic ordering, absorbing phase transition