This interaction causes triplet spin states to have lower energy than singlet states. For 10 points each:
[10h] Name this interaction caused by the indistinguishability of quantum particles. By the spin-statistics theorem, fermion wavefunctions are antisymmetric under this interaction while boson wavefunctions are symmetric.
ANSWER: exchange interaction
[10m] The exchange interaction couples neighboring spins in the Ising model, which explains this phenomenon. This phenomenon occurs when domains in a solid spontaneously align.
ANSWER: ferromagnetism [prompt on magnetism]
[10e] This scientist names the Hamiltonian describing spins in a lattice and discovered the exchange interaction independently of Paul Dirac. This scientist discovered the uncertainty principle.
ANSWER: Werner Heisenberg [accept Heisenberg Hamiltonian; accept Heisenberg uncertainty principle]
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