Advanced memory effects in the aging of a polymer glass

A new kind of memory effect oil low frequency dielectric measurements oil plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant epsilon. A temporary stop of cooling produces a downward relaxation of epsilon. Two main features are observed (i) when cooling is resumed epsilon goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) (ii) upon reheating epsilon keeps the memory of all the cooling stops (Advanced memory). The dependence of this effect on frequency and oil the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.