Field-induced gap in ordered Heisenberg antiferromagnets

Abstract

Heisenberg antiferromagnets in a strong uniform magnetic field $H$ are expected to exhibit a gapless phase with a global O(2) symmetry. In many real magnets, a small energy gap is induced by additional interactions that can be viewed as a staggered transverse magnetic field $h=cH$, where $c$ is a small proportionality constant. We study the effects of such a perturbation, particularly for magnets with long-range order, by using several complimentary approaches: numerical diagonalizations of a model with long-range interactions, classical equations of motion, and scaling arguments. In an ordered state at zero temperature, the energy gap at first grows as $(cH{)}^{1/2}$ and then may dip to a smaller value, of order $(cH{)}^{2/3}$, at the quantum critical point separating the ``gapless'' phase from the gapped state with saturated magnetization. In one spatial dimension, the latter exponent changes to 4/5.

6 pages, 5 figures

References in corpus (1)

• Coupled $S=1/2$ Heisenberg antiferromagnetic chains in an effective staggered field

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