Dynamical solutions of a quantum Heisenberg spin glass model

Details Dynamical solutions of a quantum Heisenberg spin glass model Dynamical solutions of a quantum Heisenberg spin glass model

2004-07-13

arxiv.org/abs/cond-mat/0407328v1

Physics

Condensed Matter

Statistical Mechanics

8 pages, 7 figures

Scientific paper

10.1140/epjb/e2004-00346-y

We consider quantum-dynamical phenomena in the $\mathrm{SU}(2)$, $S=1/2$ infinite-range quantum Heisenberg spin glass. For a fermionic generalization of the model we formulate generic dynamical self-consistency equations. Using the Popov-Fedotov trick to eliminate contributions of the non-magnetic fermionic states we study in particular the isotropic model variant on the spin space. Two complementary approximation schemes are applied: one restricts the quantum spin dynamics to a manageable number of Matsubara frequencies while the other employs an expansion in terms of the dynamical local spin susceptibility. We accurately determine the critical temperature $T_c$ of the spin glass to paramagnet transition. We find that the dynamical correlations cause an increase of $T_c$ by 2% compared to the result obtained in the spin-static approximation. The specific heat $C(T)$ exhibits a pronounced cusp at $T_c$. Contradictory to other reports we do not observe a maximum in the $C(T)$-curve above $T_c$.

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