Loss of memory of an elastic line on its way to limit cycles

Abstract

Under an oscillating mechanical drive, an amorphous material progressively forgets its initial configuration and might eventually converge to a limit cycle. Beyond quasistatic drivings, how structurally disordered systems lose or record such memory remains theoretically challenging. Here we investigate these issues in a minimal model system -- with quenched disorder and memory encoded in a spatial pattern -- where the oscillating protocol can formally be replaced by finite positive-velocity driving. We consider an elastic line driven at zero temperature in a fixed disordered landscape, with bi-periodic boundary conditions and tunable system size. This setting allows us to control the area swept by the line at each cycle in a given disorder realisation, as would the amplitude of an oscillating drive. We find that the line converges to disorder-dependent limit cycles, jointly for its geometrical \emph{and} velocity profiles. Moreover, the way it forgets its initial condition is strongly coupled to the nature of the velocity dynamics it displays depending on system size. We conclude on the implications of these results for the response of amorphous materials under \emph{non}-quasistatic oscillating protocols.