The Two-Fluid Model of Superfluidity

Abstract

Liquid 4He presents a continuous phase transition at Tλ ≈ 2.17 K from a normal fluid (He I) to a superfluid (He II). This work explores the theoretical framework explaining He II’s unique behavior. We will focus on Landau’s two-fluid model, which treats He II as a mixture of a superfluid component with zero entropy that remains in the ground state, and a normal fluid component associated to the excitations of Helium. The model successfully explains key experimental phenomena and predicts the existence of second sound, a temperature wave unique to quantum fluids.