Superfluidity

The ability of the fluid to flow through fine capillaries without outward friction refers to superfluidity. It is one of the interesting properties of superfluid, which occurs in certain substances and under some special conditions. This property occurs in extra-terrestrial systems like neutron stars. There exists some evidence, which shows that some other terrestrial systems also hold this property like excitons. Read below to know more about the discovery of superfluid helium, theoretical explanation, and some of the examples possessing this property. 

Discovery of Superfluid Liquids

The phenomena of superfluid helium is a stimulating property, which one can observe directly in ultracold atomic gases and helium isotopes. Helium-3 and Helium-4 are the two stable isotopes of helium, which remain liquid at low pressures to absolute zero. Both isotopes exhibit the property to get superfluid's. In Helium-4, this property was discovered below 2.17 K and Helium-3 shows no signs of the property below 2.65 K temperature. American physicists Robert C. Richardson, Douglas D. Osheroff, and David M. Lee discovered that below 270.5-degree Celsius, the isotope of liquid helium superfluid has three different phases, say A, B, and C. 

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The above picture shows that liquid helium can flow through fine channels and thus acts as a superfluid.

Theoretical Explanation of Superfluid Liquids

Helium-4 isotope can flow without any friction through narrow capillaries that any ordinary liquid cannot. The phenomenon is based on the idea that an extremely large number of atoms show quantum mechanical behaviour. It means that a coherent and quantum mechanical wave function describes the system. According to quantum mechanics, a single electron cannot rotate around the nucleus in an atom. The electron should rotate in such a way so that its angular momentum is quantized and becomes a multiple of h/2π. 

Talking about examples of superfluid's, the situation is different. Helium-4 is one of the special cases in which atoms have null total spin angular momentum, and the distribution between different states is governed by Bose statistics principle. Without any interactions, a gas of such atoms would undergo Bose condensation at some temperature To. Below this temperature, some fraction of all the atoms occupy one state, often the lowest energy state. The fraction of atoms starts increasing as the temperature falls towards absolute zero. These atoms are known to be condensed. 

A similar phenomenon is observed for a liquid such as Helium-4. When this liquid flows through a narrow capillary, the walls of the channel cannot scatter the condensed atoms one at a time. It is because these atoms are enforced by Bose statistics to reside in the same state. As this type of process is quite unconvincing, the liquid flows through small channels without apparent friction. 

Properties of Superfluid's

A superfluid acts as a mixture of an ordinary element possessing standard fluid properties along with a superfluid component. The entropy, as well as viscosity possessed by the superfluid factor, is zero. Following are some of the well-known properties of superfluid liquids:

• Film Flow:

Alcohol and petroleum are some of the ordinary liquids that slink up matter walls due to their surface tension. The same property is observed in liquid helium, but the flow of the liquid is restricted by critical viscosity, not by its own. The critical velocity is about 20 cm/s, due to which Helium can flow effortlessly up the walls of containers. 

• Rotation: 

When a super liquid is placed in a rotating container, a remarkable property becomes visible. On rotating the channel at a speed less than the critical velocity, the liquid remains motionless instead of rotating. When the first critical angular velocity is reached, the liquid comes into the rotating state that consists of quantized vortices. It implies that superfluid can spin at certain values. 

Superfluidity and Superconductivity - Is There Any Relation Between Them?

According to modern science, superconductivity is like a superfluid phenomenon that ascends in electrically charged systems. The term superconductivity means that an electric current can flow without any resistance like a super liquid, which can flow down a narrow channel without any friction. The phenomenon of superconductivity exists in various metals like Nb, Al, and Sn at low temperatures. It occurs due to the movement of conduction electrons without any resistance in a metal. So, one can understand this phenomenon as superfluidity of the conduction electrons. 

Final Thoughts

Superfluid refers to the state of matter in which the matter possesses the properties of liquid with zero viscosity. There exists some connection between superconductors and superfluids. One can understand the superconductivity phenomenon as a superfluid occurring in an electrically charged system.