Physical Review B
Ground state and low-lying excitations in a Heisenberg spin-glass model in three dimensions
Fumitaka Matsubara, Takayuki Shirakura, S. Takahashi, Y. Baba
Abstract
We developed a hybrid genetic algorithm and studied the ground state and low-lying excitations of the $\ifmmode\pm\else\textpm\fi{}J$ Heisenberg model on a three-dimensional $L\ifmmode\times\else\texttimes\fi{}L\ifmmode\times\else\texttimes\fi{}L(L\ensuremath{\leqslant}11)$ lattice. Our results suggest occurrence of a Parisi state. That is, there exists a metastable state with a finite energy of $\ensuremath{\Delta}E\ensuremath{\sim}O(J)$ in the thermodynamic limit and the energy barrier $\ensuremath{\Delta}W$ between the metastable state and the ground state is $\ensuremath{\Delta}W\ensuremath{\propto}J{L}^{\ensuremath{\theta}}$ with $\ensuremath{\theta}\ensuremath{\sim}0.53$. Our results also suggest that the energy $\ensuremath{\Delta}E$ of small scale excitations are related to a scale of the excitation $V$ in a similar manner to those of the ferromagnetic model, i.e., $\ensuremath{\Delta}E\ensuremath{\propto}J{L}^{{\ensuremath{\theta}}_{L}}{V}^{{\ensuremath{\theta}}_{v}}$ with ${\ensuremath{\theta}}_{L}\ensuremath{\sim}\ensuremath{-}4.7$ and ${\ensuremath{\theta}}_{v}\ensuremath{\sim}2.0$. This fact suggests that similarity exists in the ground state structure between the $\ifmmode\pm\else\textpm\fi{}J$ and the ferromagnetic Heisenberg models, though the spin directions of those two models differ greatly from one another.