## Superfluidity Superfluidity is a notable property of . It is characterized by **zero viscosity**, which allows the condensate to flow without resistance. This phenomenon is observed when certain fluids are cooled to extremely low temperatures, close to **absolute zero** ($0\ \text{K}$ or $-273^\circ\text{C}$). In the context of Helium-4, the transition to superfluidity occurs at a specific temperature known as the **Lambda Point ($\lambda$-point)**, which is approximately $2.17\ \text{K}$. Above this temperature, Helium behaves as a normal liquid (Helium I), but below it, it becomes a superfluid (Helium II). ## Key Features Superfluidity exhibits the following special qualities: 1. **Flow through small spaces**: The superfluid can pass through incredibly small capillaries or pores at a steady speed without any external pressure or forces applied, due to its zero viscosity. 2. **Persistent vortices**: The superfluid has the ability to form vortices that persist for extended periods because there is no internal friction to dissipate the energy. 3. **Rollin Film Effect**: A superfluid can spontaneously form a thin film (about 30 nm thick) that "climbs" up the walls of a container, effectively escaping the vessel. 4. **Infinite Thermal Conductivity**: Superfluids can transfer heat extremely efficiently without any temperature gradient, which causes the liquid to stop boiling (bubbling) and become perfectly still as it transitions past the $\lambda$-point. ## Definition of Vortex In fluid dynamics, a **vortex** is a region in a fluid where the flow revolves around an axis line, which may be straight or curved. In superfluids, these vortices are "quantized," meaning they can only exist at specific, discrete strengths.