Cooling metals to the microkelvin regime, then and now

Better understanding of the behaviour of materials and the techniques of nu clear cooling, gained in recent years, now allows us to cool metallic sampl es to the microkelvin regime, with hold times at the higher temperatures of tens of hours. In the early days of nuclear cooling when sources of heat l eaks were hardly understood, such performance would have appeared an imposs ible dream. However, we are now at the point where solid state experiments can be realistically contemplated in the sub-10 mu K regime. (C) 2000 Publi shed by Elsevier Science B.V. All rights reserved.