The λ point of helium-4 is around 2.2K 4, below which it begins to exhibit such behaviors which were found to be closely linked to that of an ideal Bose-Einstein gas 3. It is at and below this point that helium can be described in its superfluid form, helium II. By reducing the pressure in the container, it causes evaporation and heat loss to occur so that temperatures under the λ point can be attained. In order to achieve these extremely low temperatures, liquid helium is cooled using a vacuum pump. Once below the λ point, liquid helium spontaneously rises up the sides and out of its containers. In order for liquid helium to diverge from the rules of classical mechanics, it has to be further cooled past a critical point known as its lambda (λ) point (Fig. It exhibits properties such as possessing viscosity, filling its container and having limited heat conduction capabilities. At temperatures just under its boiling point, liquid helium behaves like a normal liquid. Furthermore, its low atomic mass means that helium atoms tend to stay apart from each other as this decreases its ground state energy, a naturally occurring quantum phenomenon.ĭespite this, its liquid phase has been studied extensively over the years. The low temperatures required for helium to transition from a liquid to gas can be attributed to its weak interatomic forces due to it being a noble gas. Helium-4, the most common isotope of helium, has a boiling point of just 4.2 K under standard atmospheric pressure. The rate of transfer is dependent on temperature and hence in an undisturbed system, this flow equilibrates as a linear function against time. This was shown to form a film that creeps out of the sides of a container owing to a thermodynamically reversible process. This superfluid phase possesses an extremely high heat capacity and conductivity due to its unique mechanism of heat transfer as a flow of entropy. Tl dr: As a container of liquid helium is cooled past its λ point, a fraction of its particles ‘condense’ and exist in their lowest energy state.
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