LandauTiszamodel

The Landau–Tisza model is a phenomenological description of superfluidity that combines key ideas from the two-fluid concept introduced by László Tisza and the excitation-focused hydrodynamic theory developed by Lev Landau. It treats a superfluid as an interpenetrating mixture of a viscous "normal" component, which carries entropy, and an inviscid "superfluid" component, which flows without dissipation. Each component has its own density and velocity fields and together satisfy conservation of mass, momentum and energy.

Historically, Tisza proposed the two-fluid picture to explain the unusual thermal and transport properties of liquid helium II, while Landau refined the approach by identifying a spectrum of elementary excitations (phonons and rotons) that determine the normal-fluid behavior and set a critical velocity for dissipation. The combined Landau–Tisza framework emphasizes macroscopic hydrodynamics constrained by the excitation spectrum rather than assuming Bose–Einstein condensation as the sole origin of superfluidity.

Predictions of the model include the existence of second sound (an entropy or temperature wave), the fountain effect, and characteristic relations between superfluid fraction and temperature. It successfully accounts for many low-temperature experimental observations in helium-4.

Limitations include its phenomenological nature and limited microscopic justification in some regimes; later quantum many-body and field-theoretic treatments have provided deeper foundations and corrections. Nonetheless, the Landau–Tisza model remains a cornerstone of the theoretical description of quantum fluids and a useful basis for understanding superfluid hydrodynamics.