Dynamical solutions of a quantum Heisenberg spin glass model

TL;DR

This paper investigates the quantum dynamics of an SU(2), S=1/2 infinite-range quantum Heisenberg spin glass, deriving self-consistency equations, and analyzing the critical temperature and specific heat behavior with dynamical correlations.

Contribution

The study formulates dynamical self-consistency equations for a quantum Heisenberg spin glass and assesses the impact of dynamical correlations on the critical temperature and specific heat.

Findings

Dynamical correlations increase the critical temperature by 2%.

The specific heat shows a cusp at the transition temperature.

No maximum in specific heat above the transition temperature was observed.

Abstract

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 $T_c$.