  Repeated/cyclic shearing can drive amorphous solids to a steady-state
encoding a memory of the applied strain amplitude. However, recent experiments
find that the effect of such memory formation on the mechanical properties of
the bulk material is rather weak. Here we study the memory effect in a yield
stress solid formed by a dense suspension of cornstarch particles in paraffin
oil. Under cyclic shear, the system evolves towards a steady-state showing
training-induced strain stiffening and plasticity. A readout reveals that the
system encodes a strong memory of the training amplitude as indicated by a
large change in the differential shear modulus. We observe that memory can be
encoded for a wide range of training amplitude both above and below the
yielding, albeit, the strength of the memory decreases with increasing the
training amplitude. In-situ boundary imaging shows strain localization close to
the shearing boundaries, while the bulk of the sample moves like a solid plug.
In the steady-state, the average particle velocity (<v>) inside the solid-like
region slows down with respect to the moving plate as the strain approaches the
training amplitude, however, as the readout strain crosses the amplitude, <v>
suddenly increases. We demonstrate that inter-particle adhesive interaction is
crucial for such a strong memory effect. Interestingly, our system can also
remember more than one input only if the training strain with a smaller
amplitude is applied last.
