Rotons and Phonons

Rotons and phonons are the elementary excitations of superfluid helium. Phonons are high frequency sound waves. Rotons are excitations with a very short wavelength (around 3Ã…) about the same as the spacing between the helium atoms in the liquid. At temperatures of 1 K and above, it is the rotons which make the main contribution to the specific heat and the thermal energy.