Hysteretic response to different modes of ramping an external field in sparse and dense Ising spin glasses

Abstract

We consider the hysteretic behavior of Ising spin glasses at $T=0$ for various modes of driving. Previous studies mostly focused on an infinitely slow speed $\dot{H}$ by which the external field $H$ was ramped to trigger avalanches of spin flips by starting with destabilizing a single spin while few have focused on the effect of different driving methods. First, we show that this conventional protocol imposes a system size dependence. Then, we numerically analyze the response of Ising spin glasses at rates $\dot{H}$ that are fixed as well, to elucidate the differences in the response. Specifically, we compare three different modes of ramping ($\dot{H}=c/N$, $\dot{H}=c/\sqrt{N}$, and $\dot{H}=c$ for constant $c$) for two types of spin glass systems of size $N$, representing dense networks by the Sherrington-Kirkpatrick model and sparse networks by the lattice spin glass in $d=3$ dimensions known as the Edwards Anderson model. Depending on the mode of ramping, we find that the response of each system, in form of spin-flip avalanches and other observables, can vary considerably. In particular, in the $N$-independent mode applied to the lattice spin glass, which is closest to experimental reality, we observe a percolation transition with a broad avalanche distribution between phases of localized and system-spanning responses. We explore implications for combinatorial optimization problems pertaining to sparse systems.