title: Fluctuation-dissipation ratio of a spin glass in the aging regime.
abstract: We present the first experimental determination of the time autocorrelation C(t',t) of magnetization in the nonstationary regime of a spin glass. Quantitative comparison with the response, the magnetic susceptibility chi(t',t), is made by using a new experimental setup allowing both measurements in the same conditions. Clearly, we observe a nonlinear fluctuation-dissipation relation between C and chi, depending weakly on the waiting time t'. Following theoretical developments on mean-field models, and lately on short range ones, it is predicted that in the limit of long times the chi(C) relationship should become independent of t'. A scaling procedure allows us to extrapolate to the limit of long waiting times.
authors.affiliation: DSM/Service de Physique de l'Etat Condensé, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France.
authors.forename: D
authors.initials: D
authors.lastname: Hérisson
authors.forename: M
authors.initials: M
authors.lastname: Ocio