Eur. Phys. J. B 41, 525-533 (2004)
https://doi.org/10.1140/epjb/e2004-00346-y

Dynamical solutions of a quantum Heisenberg spin glass model

Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Federal Republic of Germany

Corresponding author: ^a bechmann@physik.uni-wuerzburg.de

Received: 13 July 2004
Published online: 5 November 2004

Abstract

We consider quantum-dynamical phenomena in the , 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 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.