Quasifluid

Quasifluid is a term used in physics to describe a state or description of matter in which macroscopic flow properties resemble those of a classical fluid, but the underlying degrees of freedom are not a simple liquid. Instead, the fluid-like behavior arises from many-body interactions among quasi-particles or collective quantum states, producing an emergent, coarse-grained velocity field.

The concept rests on hydrodynamic descriptions that become valid when momentum-conserving collisions dominate over momentum-relaxing processes, allowing a Navier–Stokes–like framework with an effective viscosity and conductivity. In such regimes, the system can exhibit continuous flow, diffusion, and other fluid-like phenomena even though its microscopic constituents are quantum or strongly correlated.

Quasifluid behavior appears in several contexts. In condensed matter physics, electron fluids in metals and graphene can display viscous flow and nonlocal transport. Ultracold atomic gases at strong interactions offer clean platforms to study hydrodynamic regimes. Related ideas arise in strongly coupled plasmas and other many-body quantum systems where collective motion dominates single-particle dynamics.

Observables signaling quasifluid dynamics include collective flow profiles in confined geometries, signatures of low effective viscosity, and transport that aligns with hydrodynamic predictions. The term is not universally standardized; some researchers prefer "quantum fluid" or "electron hydrodynamics" for related ideas. In all uses, quasifluid emphasizes emergent, large-scale fluid behavior arising from microscopic interactions.

See also: hydrodynamics, quantum fluids, quasi-particles, electron hydrodynamics.