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6. LIQUID HELIUM(-4) What happens when you have a material made of bosonic atoms that remains liquid all the way down to zero temperature? It becomes a "superfluid" and does crazy things like: - climb the walls of its container and empty itself onto the floor ("fountain effect")
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- If you put it in a bucket, and then start rotating the bucket, the superfluid will remain completely still. Then, at a critical rotation frequency, the fluid will start to develop quantized vortices.
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7. LIQUID HELIUM-3 This is a distinct form of helium, purified so that it only has fermionic atoms (1 neutron per atom instead of 2). It isn't supposed to become a superfluid because it is made of fermions, which cannot undergo Bose condensation. But He-3 goes superfluid anyway.
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Somehow, two fermionic atoms bind to each other (in a process analogous to superconductivity, where two electrons bind together), to make "composite bosons". These composite bosons form a superfluid.
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Another crazy thing about He-3: at low-T its solid phase has more entropy than its liquid phase. (I know, this violates everything your high school chemistry teacher taught you about what entropy is) This means that, under the right conditions, He-3 _freezes_ when you heat it up
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Iron is especially difficult because it contains both magnetism and freely-conducting electrons. This is something we still don't have a good theory of. So far our theories of magnetism are mostly built to describe little bar magnets (the electrons themselves) frozen in place.
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9. COPPER To me, the funniest thing about copper is always that it turns green when it rusts. So our Statue of Libery started out looking like a flaming beacon of hope and quickly turned into Kermit the frog.
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Here's something else weird about copper. Electrons in its interior are flying around at (literally) a million miles per hour. If you take a census of their momentum, you'll find that all the values sit neatly inside a geometric surface ("Fermi surface") that looks like this:
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