Microkelvin physics

This review is concerned with the techniques and physical problems associated with the temperature range below 200 μK. First, we treat the basic physics of nuclear cooling. Then we introduce some of the experimental difficulties and discuss how these problems can be solved in practice, ending with a discussion of several cryostats which have been designed for this temperature regime. In the second part of the review we take a look at a selection of physical topics which are of interest below 200 μK, those chosen being superfluid 3He, 3He-4He solutions and magnetic ordering in solid 3He. (author)