Abstract

We analyze the infinite range Ising spin glass in a transverse field Γ by using Grassmann variables in a field theory where the spin operators are represented by bilinear combinations of fermionic fields. We compare the results of two fermionic models. In the four state (4S)-model the diagonal S i z operator has two vanishing eigenvalues, that are suppressed by a restraint in the two states (2S)-model. Within a replica symmetric theory and in the static approximation we obtain qualitatively similar results for both models. They both exhibit a critical temperature T c ( Γ) that decreases when Γ increases, until it reaches a quantum critical point at the same value of Γ c and they are both unstable under replica symmetry breaking in the whole spin glass phase. Our results are in agreement with recent renormalization group calculations in three-dimensional systems.

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