Replica symmetry breaking in the transverse-field Ising spin-glass   model: Two frmionic representations
  We analyze the infinite range Ising spin-glass in a transverse-field below the critical temperature by a one step replica symmetry theory(1S-RSB). The set of n replicas is divided in r blocks of m replicas each. We present results for different values of the block-size parameter m. The spin operators are represented by bilinear combinations of fermionic fields and we compare the results of two models: in the four state (4S)-model the diagonal S^z operator has two unphysical vanishing eigenvalues, that are suppressed by a restraint in the two states (2S)-model. In the static approximation we obtain qualitatively similar results for both models. They both exhibit a critical temperature that decreases when the transverse field increases,until it reaches a quantum critical point (QCP) at the same value of the critical field, and they are both unstable under replica symmetry breaking in the whole spin glass phase. Below the critical temperature we present results for the order parameters and free energy. 
Eduardo M.M.Santos and Alba Theumann