Reversible to Irreversible Flow Transition of Periodically Driven Vortices in the Strip Sample

Dobroka

Shirahata

et al. 2017

J. Phys.: Conf. Ser.

Abstract. Many colliding particles that are periodically sheared by ac drive self-organize to avoid future collisions, which is known as random organization. Recently, we have observed the random organization in the vortex system of a strip-shaped amorphous MoxGe1−x film, where the vortices experience periodic local shear from ac drive and the random pinning potential. In this work, we study how random organization changes in the vortex system under the tilted field, where an anisotropic vortex-vortex interaction is introduced. We find that characteristic times of random organization for the vortices driven in the tilted direction are significantly smaller than those in the untilted field.

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See 3 more Smart Citations

Random organization of vortices under an anisotropic condition

Dobroka

Shirahata

et al. 2017

J. Phys.: Conf. Ser.

Critical behavior near the reversible-irreversible transition in periodically driven vortices under random local shear

Maegochi

Kaneko

et al. 2019

Sci Rep

Self Cite

When many-particle (vortex) assemblies with disordered distribution are subjected to a periodic shear with a small amplitude , the particles gradually self-organize to avoid next collisions and transform into an organized configuration. We can detect it from the time-dependent voltage (average velocity) that increases towards a steady-state value. For small , the particles 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 above a threshold . Here, we investigate the general phenomenon of a reversible-irreversible transition (RIT) using periodically driven vortices in a strip-shaped amorphous film with random pinning that causes local shear, as a function of . By measuring , we observe a critical behavior of RIT, not only on the irreversible side, but also on the reversible side of the transition, which is the first under random local shear. The relaxation time to reach either the reversible or irreversible state shows a power-law divergence at . The critical exponent is determined with higher accuracy and is, within errors, in agreement with the value expected for an absorbing phase transition in the two-dimensional directed-percolation universality class. As is decreased down to the intervortex spacing in the reversible regime, deviates downward from the power-law relation, reflecting the suppression of intervortex collisions. We also suggest the possibility of a narrow smectic-flow regime, which is predicted to intervene between fully reversible and irreversible flow.

Critical behavior of density-driven and shear-driven reversible–irreversible transitions in cyclically sheared vortices

Maegochi

Okuma

2021

Sci Rep

Random assemblies of particles subjected to cyclic shear undergo a reversible–irreversible transition (RIT) with increasing a shear amplitude d or particle density n, while the latter type of RIT has not been verified experimentally. Here, we measure the time-dependent velocity of cyclically sheared vortices and observe the critical behavior of RIT driven by vortex density B as well as d. At the critical point of each RIT, $$B_{\mathrm {c}}$$ B c and $$d_{\mathrm {c}}$$ d c , the relaxation time $$\tau $$ τ to reach the steady state shows a power-law divergence. The critical exponent for B-driven RIT is in agreement with that for d-driven RIT and both types of RIT fall into the same universality class as the absorbing transition in the two-dimensional directed-percolation universality class. As d is decreased to the average intervortex spacing in the reversible regime, $$\tau (d)$$ τ ( d ) shows a significant drop, indicating a transition or crossover from a loop-reversible state with vortex-vortex collisions to a collisionless point-reversible state. In either regime, $$\tau (d)$$ τ ( d ) exhibits a power-law divergence at the same $$d_{\mathrm {c}}$$ d c with nearly the same exponent.