Dynamical properties of the Haldane chain with bond disorder |
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Authors: | Jing-Kai Fang Jun-Han Huang Han-Qing Wu Dao-Xin Yao |
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Institution: | 1. Center for Neutron Science and Technology, School of Physics, Sun Yat-sen University, Guangzhou 510275, China2. State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics, Sun Yat-sen University, Guangzhou 510275, China |
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Abstract: | 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 δ? ~ 0.5 with more and more low-energy excitations coming out. After the critical disorder strength δc ~ 1, the system reaches a random-singlet phase with prominent sharp peak at ω = 0 and broad continuum at ω > 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 longrange singlets due to quantum fluctuation which contribute to the sharp peak at ω = 0. |
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Keywords: | Haldane chain Heisenberg model magnetic excitation quantum phase transition random singlet disorder exact diagonalization quantum Monte Carlo |
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