Spin Domains Generate Hierarchical Ground State Structure in J=+/-1 Spin   Glasses
  Unbiased samples of ground states were generated for the short-range Ising spin glass with Jij=+/-1, in three dimensions. Clustering the ground states revealed their hierarchical structure, which is explained by correlated spin domains, serving as cores for macroscopic zero energy "excitations". 
Guy Hed, Alexander K. Hartmann, Dietrich Stauffer and Eytan Domany