An historical account of the two-fluid theory for superfluidity

In 1924, Einstein showed the theoretical possibility of the three-dimensional Bose-Einstein condensate, for mass particles. When published, his work did not attract the scientific community, until approximately ten years later, when Fritz London retook it along with Laszlo Tisza, to generate a theory able to explain the superfluidity in terms of two fluids: one formed by atoms within the condensate state, and the second formed with atoms in the normal state. Later, under the commitment of Kapitsa, Landau began the research about the superfluidity problem, with conceptually different assumptions than those of London and Tisza. Landau thought that atoms are the medium in which excitations are propagated, through a two-fluid model. The development of such theories took place in the 1930s and 1940s, when Europe was convulsed by political and social problems. In this work, we clarify the differences between both models, usually confused, and we analyse the influence of the historical reality in which the main scientific actors that gave birth to such theories were involved, elucidating why the path initiated by Einstein, ended in two different intents to describe the superfluidity phenomenon: two two-fluid theories. April is the cruellest month... Thomas S.