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Frustrated antiferromagnets at high fields: the Bose-Einstein condensation in degenerate spectra

G. Jackeli·M. E. Zhitomirsky
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Abstract

Quantum phase transition at the saturation field is studied for a class of frustrated quantum antiferromagnets. The considered models include (i) the $J_1$-$J_2$ frustrated square-lattice antiferromagnet with $J_2={1/2}J_1$ and (ii) the nearest-neighbor Heisenberg antiferromagnet on a face centered cubic lattice. In the fully saturated phase the magnon spectra for the two models have lines of degenerate minima. Transition into partially magnetized state is treated via a mapping to a dilute gas of hard core bosons and by complementary spin-wave calculations. Momentum dependence of the exact four-point boson vertex removes the degeneracy of the single-particle excitation spectra and selects the ordering wave-vectors at $(π,π)$ and $(π,0,0)$ for the two models. The asymptotic behavior of the magnetization curve differs significantly from that of conventional antiferromagnet in $d$-spatial dimensions. We predict a unique form for the magnetization curve $ΔM=S-M\simeq μ^{(d-1)/2}(\logμ)^{(d-1)}$, where $μ$ is a distance from the quantum critical point.

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G. Jackeli, M. E. Zhitomirsky. 2004-05-13. Frustrated antiferromagnets at high fields: the Bose-Einstein condensation in degenerate spectra. https://doi.org/10.1103/physrevlett.93.017201

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