Nonequilibrium dynamics of spin glasses and the observability of spin-glass correlations in simple magnetic scattering (invited)

A theory, developed in collaboration with Fisher, of the nonequilibrium behavior of spin glasses for temperatures, T, below the ordering temperature, T_g, is first reviewed. The magnetic structure factor, S(q), of a spin glass that is magnetized either due to the presence of a uniform magnetic field, h, or due to having been field cooled to T<T_g is then examined. It is found that long-range spin-glass correlations, if present, are directly observable in S(q) whenever the sample is magnetized. For example, for T>T_g, h=0, and 0<q≪ξ^-1_s, where ξ_s is the correlation length of any short-range (e.g., spin-density wave, ferro- or antiferromagnetic) order, d²S(q)/dh ²∝-Ĝ_EA(q), where Ĝ_EA(q) is the Fourier transform of the usual Edwards-Anderson (spin-glass) correlation function. Thus, one can, in principle, directly measure (a) the spin-glass correlation length when the sample is at equilibrium, and (b) the nonequilibrium spin-glass correlation length (domain size) when the sample is in a nonequilibrium state produced by field cooling.