2. Spin Waves and Magnons


We have already seen that extreme conditions are necessary to obtain Bose Einstein condensation in atomic gases. The instrumentation needed is highly complex and extremely expensive. An ultra high vacuum chamber is needed to avoid interactions between trapped and free atoms. The appropriate lasers are highly stable single frequency lasers with tunable frequency which makes them very expensive. Together with all the controlling units such a system for Bose Einstein condensation can cost up to a few million dollars.

I already pointed out in section 1c) that atoms are not the only particles that can form a gas. Electrons in a conductor can also be treated as a gas. Though electrons have spin ½ and therefore obey Fermi-Dirac statistics so they are no candidates for BEC.

We have also seen that in quantum mechanics particles behave like waves. This statement can also be flipped so in quantum mechanics sometimes waves behave like particles.

In this chapter I will treat a special kind of waves, called Spin Waves (SW). The elementary particle of which is the magnon. Magnons have a spin equal to one and therefore obey Bose-Einstein statistics and are very good candidates for Bose-Einstein condensation under less extreme conditions. The first section treats the question:

What are Spin Waves?