In this work, the normal density ρ n and moment of inertia of a moving superfluid are investigated. We find that, even at zero temperature, there exists a finite normal density for the moving superfluid. When the velocity of superfluid reaches sound velocity, the normal density becomes total mass density ρ , which indicates that the system losses superfluidity. At the same time, the Landau’s critical velocity also becomes zero. The existence of the non-zero normal density is attributed to the coupling between the motion of superflow and density fluctuation in transverse directions. With Josephson relation, the superfluid density ρ s is also calculated and the identity ρ s + ρ n = ρ holds. Further more, we find that the finite normal density also results in a quantized moment of inertia in a moving superfluid trapped by a ring. The normal density and moment of inertia at zero temperature could be...

中文翻译：

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运动超流体的法向密度和惯性矩

在这项工作中，研究了移动超流体的法向密度ρn和惯性矩。我们发现，即使在零温度下，移动的超流体也存在有限的法向密度。当超流体的速度达到声速时，正常密度变为总质量密度ρ，这表明系统失去了超流体。同时，兰道的临界速度也变为零。非零法向密度的存在归因于超流运动与横向密度波动之间的耦合。利用约瑟夫森关系，还可以计算出超流体密度ρs，并且恒等式ρs +ρn =ρ成立。此外，我们发现有限的法向密度还会在被环捕获的运动超流体中产生量化的惯性矩。