However, for the cases of helium-4 and its isotope helium-3, there is a pressure range where they can remain liquid down to absolute zero because the amplitude of the quantum fluctuations experienced by the helium atoms is larger than the inter-atomic distances.
One prominent example is that of superconductivity where quasi-particles made up of pairs of electrons and a phonon act as bosons which are then capable of collapsing into the ground state to establish a supercurrent with a resistivity near zero.
Quantum mechanical effects become significant for physics in the range of the de Broglie wavelength.
Mathematically, this is stated like so: It is easy to see how the above definition relates to the particle density, n. We can write as
is an estimation of the Fermi energy of the system, where processes important to phenomena such as superconductivity take place.