Distribution of local Lyapunov exponents in spin-glass dynamics

Abstract

We investigate the statistical properties of local Lyapunov exponents which characterize magnon localization in the one-dimensional Heisenberg-Mattis spin glass HMSG at zero temperature by means of a connection to a suitable version of the Fokker-Planck FP equation. We consider the local Lyapunov exponents LLEs ,i n particular, the case of instantaneous LLE. We establish a connection between the transfer-matrix recursion relation for the problem and an FP equation governing the evolution of the probability distribution of the instantaneous LLE. The closed-form stationary solutions to the FP equation are in excellent accord with numerical simulations for both the unmagnetized and magnetized versions of the HMSG. Scaling properties for nonstationary conditions are derived from the FP equation in a special limit in which diffusive effects tend to vanish, and also shown to provide a close description to the corresponding numerical-simulation data. I. INTRODUCTION The analytic treatment of quenched disordered systems in condensed-matter physics invokes many concepts from statistical theory. Among these, we shall be concerned in this paper with the connection between the probability distribution of Lyapunov characteristic exponents for the equilibrium problem of low-lying magnetic excitations in spin glasses, and the Fokker-Planck FP equation, 1 which is a key element in the description of nonequilibrium stochastic