Mechanical annealing and multiple memories in an amorphous solid

Studies of amorphous or disordered jammed solids have shown that applying many cycles of oscillatory shear can train or anneal them, leading to a steady state with periodic particle motions. However, this process leaves an imprint of the annealing strain amplitude and of a direction of shear. In experiments with a 2D amorphous soft solid, we show that an alternative "ring-down" annealing protocol with progressively smaller amplitudes suppresses this imprint, resulting in a symmetric microstructure, and disentangling the memory of annealing from a more general behavior called return-point memory. Based on this protocol, we introduce a test of the minimum separation between multiple memories, and show that it agrees with independent measurements of the rearranging soft spots within an experimental sample.