The Expansion Coefficient of Liquid Helium 3 and the Shape of Its Stability Limit

We propose the existence of a new feature in the phase diagram of liquid helium 3. Instead of being monotonic in temperature, the liquid-gas spinodal line should present a minimum at 0.4 K. In analogy with cold water where this was proposed by Speedy, we explain that such a minimum is a consequence of the thermal expansion coefficient being negative down to the spinodal line. We justify this from a comparison with our recent measurements of the temperature dependence of cavitation in liquid helium 3 and from new theoretical arguments.