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The helicity modulus (superfluid density) is evaluated for spin systems in the magnon regime and for an interacting Bose fluid in the Bogoliubov approximation. The quantal XY model and the Bose system each yield the same temperature dependence for the helicity modulus; the behaviour is distinct from that of the square of the order parameter.
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Banavar et al. (1978) studied this question.
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