445lec28 - PHYS 445 Lecture 28 - Superfluids Lecture 28 -...

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PHYS 445 Lecture 28 - Superfluids 28 - 1 © 2001 by David Boal, Simon Fraser University. All rights reserved; further resale or copying is strictly prohibited. Lecture 28 - Superfluids What's Important: 4 He condensation superfluids Bose-Einstein condensation Text : Reif 4 He condensation As 4 He is cooled, it undergoes a phase transition to a liquid state (referred to as He I ) at T = 4.2 K. Upon further cooling (less than 2.2 K at 1 atm pressure), He I changes to He II, also a liquid. He II is not a normal liquid, and is referred to as a superfluid. Superfluids are characterized by high heat conductivity superleaks (can flow through holes 100 Å across) low viscosity (no gradient across fluid when it flows through a pipe) Such behavior is collective, in that there is little relative motion. It is thought that superfluid He II is a Bose-Einstein condensate in which most atoms are in their ground state so that they move cooperatively. Bose-Einstein condensates
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445lec28 - PHYS 445 Lecture 28 - Superfluids Lecture 28 -...

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