Mean field theory of dilute spin-glasses with power-law interactions

The authors argue that in order to describe dilute dipolar or RKKY spin-glasses, a broad distribution of couplings (i.e decaying as a power law) is more appropriate than the traditional Gaussian distribution. They present a mean-field 'replica symmetric' theory for this problem. They find that the spin-glass transition is of a different nature than the one occurring in the SK model, and resembles a percolation transition. The deAlmeida-Thouless temperature is lower than the spin-glass transition temperature. The degree of 'replica symmetry breaking', measured by the absolute value of the negative entropy is found to be smaller than in the SK model and nonmonotonic with temperature. Some experimental consequences are briefly addressed.