Depression of the superfluid transition in4He
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We study superfluid4He near Tλ in a homogeneous metastable state where a finite superfluid velocity vs is present. Neglecting vortices we perform a renormalization-group calculation of the critical velocity vsc(T) at which the superfluid state becomes unstable. We apply this result to the situation where the superfluid velocity is induced by a finite heat current Q. A critical heat current Qc(T) corresponding to vsc(T) is found which implies a transition temperature Tλ (Q)=Tλ[1−AoQx]. We determine the exact exponent x=[(d−1)v]−1 ≈0.744 in d=3 dimensions and calculate Ao in one-loop order. Our results for Ao and x are compared with recent experimental data.
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