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Problem: Spin Waves Again

    Derive the Heisenberg Hamiltonian in the Dyson-Maleev representation of spins. Neglect the terms containing more than two boson operators, and determine the elementary excitations of the system. Under what circumstances is this approximation justified? (The Heisenberg Hamiltonian is tex2html_wrap_inline6339 ; the Dyson-Maleev representation expresses the spin operator at site i as tex2html_wrap_inline6343 , tex2html_wrap_inline6345 and tex2html_wrap_inline6347 , where tex2html_wrap_inline6349 and tex2html_wrap_inline6351 are boson creation and annihilation operators, in units of tex2html_wrap_inline6353 .)gif  

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Laszlo Mihaly
Thu Oct 31 13:23:11 EST 1996

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