Introduction to 4He
Phase Diagram of 4He
Basics of 4He
4He liquefies at 4.2K and remains a liquid down to absolute
4He undergoes a superfluid phase transition at 2.17K known as
the lambda transition.
As a superfluid, this liquid can flow without dissipation (zero viscosity!)
through very small holes, long narrow paths, and sinters. Just like superconductors,
currents can persist in loops indefinitely.
Experimentally, it is observed that superflow is stable for currents less
than some critical current. The value of this critical current
is fixed for a given experimental setup. However, this critical current
does not have a universal value and depends on the details of each particular
Updated October 25, 1999
Send comments or questions to: Richard