Book contents
- Frontmatter
- Contents
- Contributors
- Editor’s acknowledgements
- Introduction: The new physics for the Twenty-First Century
- I Matter and the Universe
- II Quantum matter
- 6 Manipulating atoms with photons
- 7 The quantum world of ultra-cold atoms
- 8 Superfluids
- 9 Quantum phase transitions
- III Quanta in action
- IV Calculation and computation
- V Science in action
- Index
- References
8 - Superfluids
Published online by Cambridge University Press: 05 June 2014
- Frontmatter
- Contents
- Contributors
- Editor’s acknowledgements
- Introduction: The new physics for the Twenty-First Century
- I Matter and the Universe
- II Quantum matter
- 6 Manipulating atoms with photons
- 7 The quantum world of ultra-cold atoms
- 8 Superfluids
- 9 Quantum phase transitions
- III Quanta in action
- IV Calculation and computation
- V Science in action
- Index
- References
Summary
What is a superfluid?
The word “superfluid” was coined to describe a qualitatively different state of a fluid that can occur at low temperatures, in which the resistance to flow is identically zero, so that flow round a closed path lasts for ever – a persistent current. Superfluidity can occur either for uncharged particles such as helium atoms or for charged particles such as the electrons in a metal. In the latter case the flow constitutes an electric current and we have a superconductor. Since an electric current is accompanied by a magnetic field, it is much easier to demonstrate the presence of a persistent current in a superconductor than in a neutral superfluid.
In this chapter I shall describe the properties of superfluids, starting with the simplest and working up to more complicated examples. But in this introductory section I shall depart from the historical order even further by turning to the last page of the detective story so as to catch a glimpse of the conclusion from almost a century of experimental and theoretical research; we shall then have an idea of where we are heading.
The conclusion is that superfluidity is more than just flow without resistance. It is an example of a transition to a more ordered state as the temperature is lowered, like the transition to ferromagnetism. At such a transition new macroscopically measurable quantities appear: in the case of a ferromagnet, the spontaneous magnetization. Such new measurable quantities are known as the order parameter of the low-temperature phase. The new quantities in the case of a superfluid are more subtle and more surprising: the amplitude and phase of the de Broglie wave associated with the motion of the superfluid particles. A superfluid can therefore exhibit quantummechanical effects on a macroscopic scale.
- Type
- Chapter
- Information
- The New PhysicsFor the Twenty-First Century, pp. 200 - 228Publisher: Cambridge University PressPrint publication year: 2006