Theory for superfluidity in a Bose system

We present a microscopic theory for superfluidity in an interacting many-particle Bose system (such as liquid ${}^4$He). We show that, similar to superconductivity in superconductors, superfluidity in a Bose system arises from pairing of particles of opposite momenta. We show the existence of an energy gap in single-particle excitation spectrum in the superfluid state and the existence of a specific heat jump at the superfluid transition. We derive an expression for superfluid particle density $n_s$ as a function of temperature $T$ and superfluid velocity ${\mathbf{v}}_s$. We show that superfluid-state free energy density $F$ is an increasing function of $v_s$ (i.e., $\mathrm{\partial }F\mathrm{/}\mathrm{\partial }{v}_s>0$), which indicates that a superfluid has a tendency to remain motionless (this result qualitatively explains the Hess-Fairbank effect, which is analogous to the Meissner effect in superconductors). We further speculate the existence of the equation ${\bf j}=-\Lambda\nabla\times $\text{boldmath}\omega$$,where${\bf j} = n_s{\bf v}_s$isthesuperfluidcurrentdensity,$\text{\boldmath $\omega$}=\nabla\times {\bf v}_s$thesuperfluidvorticity,and$\Lambda$ a positive constant (with the help of this equation, the Hess-Fairbank effect can be quantitatively described).