  When a spin glass is cooled down, a memory of the cooling process is
imprinted in the spin structure. This memory can be disclosed in a continuous
heating measurement of the ac-susceptibility. E.g., if a continuous cooling
process is intermittently halted during a certain aging time at one or two
intermediate temperatures, the trace of the previous stop(s) is recovered when
the sample is continuously re-heated [1]. However, heating the sample above the
aging temperature, but keeping it below Tg, erases the memory of the thermal
history at lower temperatures. We also show that a memory imprinted at a higher
temperature can be erased by waiting a long enough time at a lower temperature.
Predictions from two complementary spin glass descriptions, a hierarchical
phase space model and a real space droplet picture are contested with these
memory phenomena and interference effects.
  [1] K. Jonason, E. Vincent, J. Hammann, J. P. Bouchaud and P. Nordblad, Phys.
Rev. Lett. 31, 3243 (1998).
