By using the formula for Transition Temperature, we can obtain the Transition temperature for Bose Einstein Condensation to occur at 3.14 K, however, it shows the properties of superfluidity at 2.18 K. So, is the phenomenon happening after 2.18 K called BEC or not. I have read somewhere that it is called second order Transition of $\lambda$ Transition. So, is it BEC after all, since BEC is a first order Transition. Then, how can we apply the BEC in Helium 4 then. Also, is the difference in around 1K between two temperatures due to interaction.
When cooled to around 2.18K - the lambda point - liquid helium enters a superfluid phase. This is similar to a BEC, but remember that strictly speaking, BEC deals with bosons in the gas phase. In this case, since the helium is in the liquid phase, there are significant interactions between He atoms not present in the theory of a non-interacting gaseous BEC. Therefore you cannot treat the He-4 system using the same method as for a BEC. The fact that He-4 atoms are bosons is significant here however. That is why you can see superfluidity at 2.18K instead of at much lower temperatures like those required for He-3 (fermions). I hope that answers your question.