Landau's two-fluid model

Landau's two-fluid model describes superfluid helium as composed of two interpenetrating components: a "normal" fluid with viscosity and entropy, and a "superfluid" without viscosity or entropy. The normal part behaves like a conventional fluid, while the superfluid flows without resistance. These components coexist and interact, explaining phenomena like frictionless flow and thermal conductivity at very low temperatures. The model helps scientists understand how helium exhibits both liquid and superfluid behaviors simultaneously, providing a framework for studying quantum effects on a macroscopic scale.