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The clock model places a planar <unit vector> at every <lattice> site but restricts its angle to finitely many equally spaced values. Nearest-neighbour spins usually interact through the cosine of their angular difference.


Clock model

{c}
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The XY model is the infinite-state limit of the <clock model>: each spin is a <unit vector> with a continuous angle and the global symmetry is $O(2)$.


XY model

{title2=$\lVert v\rVert=1$}
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A unit vector is a <vector> whose <norm> is one.


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 Incoming links: Unit vector