Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Helium-3's Phase diagram shows that at the right temperature and pressure combination, the solid region dips downward as temperature increases. That means that you can heat it up and it will freeze. What is going on?

share|cite|improve this question
up vote 0 down vote accepted

Amazingly, below 0.3K the latent heat of fusion of $^3$He is negative i.e. you need to inject heat to make the solid freeze. This is the basis of Pomeranchuk cooling.

This is miles outside my area of expertise, but I believe it's because in the liquid you get large scale alignment of the spins called para magnons, and these lower the energy of the liquid relative to the solid.

share|cite|improve this answer
"large scale alignment of the spins called para magnons" so they lower energy and entropy so much that the solid actually is more disordered and in a higher energy state. Strange. – Kevin Kostlan Nov 10 '13 at 15:10
When it freezes you also do work. SO the He is sucking up both heat and work! – Kevin Kostlan Nov 10 '13 at 17:40

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.