A Numerical Study of Ultrametricity in Finite Dimensional Spin Glasses
  We use a constrained Monte Carlo technique to analyze ultrametric features of a 4 dimensional Edwards-Anderson spin glass with quenched couplings J=\pm 1. We find that in the large volume limit an ultrametric structure emerges quite clearly in the overlap of typical equilibrium configurations. 
Angelo Cacciuto (Cagliari, Italy), Enzo Marinari (Cagliari, Italy) and   Giorgio Parisi (Roma La Sapienza, Italy)