Dynamical properties of the Haldane chain with bond disorder

摘要

By using Lanczos exact diagonalization and quantum Monte Carlo combined with stochastic analytic continuation, we study the dynamical properties of the S = 1 antiferromagnetic Heisenberg chain with different strengths of bond disorder. In the weak disorder region, we find weakly coupled bonds which can induce additional low-energy excitation below the one-magnon mode. As the disorder increases, the average Haldane gap closes at delta(Delta) similar to 0.5 with more and more low-energy excitations coming out. After the critical disorder strength delta(c) similar to 1, the system reaches a random-singlet phase with prominent sharp peak at omega = 0 and broad continuum at omega 0 of the dynamic spin structure factor. In addition, we analyze the distribution of random spin domains and numerically find three kinds of domains hosting effective spin-1/2 quanta or spin-1 sites in between. These "spins" can form the weakly coupled long-range singlets due to quantum fluctuation which contribute to the sharp peak at omega = 0.