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Bruekner approach to the spin-wave gap critical index for the two-layer Heisenberg antiferromagnet | P.V.Shevchenko
; O.P.Sushkov
; | Date: |
28 Sep 1998 | Journal: | Phys. Rev. B 59, 8383 (1999) | Subject: | Statistical Mechanics; Superconductivity | cond-mat.stat-mech cond-mat.supr-con | Abstract: | We consider the two-layer Heisenberg antiferromagnet near a zero temperature quantum phase transition from a disordered dimer phase to a collinear Neel state. At approaching the transition point the spin-wave gap vanishes as $Delta propto (J_perp-J_{perp c})^{
u}$. To account for strong correlations between the S=1 elementary excitations we apply the Brueckner diagram approach which gives the critical index $
uapprox 0.5$. We demonstrate also that the linearized in density Brueckner equations give the mean field result $
u=1$. Finally an expansion of the Brueckner equations in powers of the density, combined with the scaling hypothesis, give $
uapprox 0.67$. This value reasonably agrees with that of the nonlinear O(3) $sigma$-model. Our approach demonstrates that for other quantum spin models the critical index can be different from that in the nonlinear $sigma$-model. We discuss the conditions for this to occur. | Source: | arXiv, cond-mat/9809368 | Services: | Forum | Review | PDF | Favorites |
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