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Finite-temperature Spin-wave Theory Of 2d Heisenberg Antiferromagnetic Model

Posted on:2011-08-29Degree:MasterType:Thesis
Country:ChinaCandidate:M M LiangFull Text:PDF
GTID:2190330332478797Subject:Theoretical Physics
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In this thesis, we present a finite-temperature spin-wave theory for two-dimensional (2D) quantum Heisenberg antiferromagnetic model. As far as the two-dimensional (2D) quantum Heisenberg antiferromagnet is concerned, its low-temperature physics is generally accepted to be determined by the spin-wave excitations upon the long-range Neel order. At high temperature, the static magnetic susceptibility shows a Curie-Weiss law. So far, an uniform theory well defined in all of the temperature region is still unknown. To solve this problem, we introduce a perturbation spin-wave theory in our thesis based upon the inspiration of Takahashi's modified spin-wave theory. We present, in details, the application of a linearized spin-wave theory on the 2D Heisenberg antiferromagnetic model in a square lattice. The temperature dependence of the free energy, internal energy, entropy, specific heat and the magnetic susceptibility are calculated. Our results at low temperature agree good with numerical quantum Monte Carlo and high-temperature series expansion method. The high-temperature results are also consistent to the numerical simulations. In this thesis, we also provide the results when the lowest-order correction of the spin-wave interaction to the energy spectrum are included. The temperature dependence of the static magnetic susceptibility agrees quantitatively with the quantum Monte Carlo. These primary results indicate that the perturbation spin-wave theory should be a good theoretical method to study the 2D quantum Heisenberg antiferromagnets.
Keywords/Search Tags:spin wave, Heisenberg antiferromagnet, specific heat, magnetic susceptibility
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