Replica Symmetry Breaking: Parisi Order Parameter
Ultrametric structure of spin glass states. q(x) encodes overlap distribution between pure states.
Parisi's RSB solution (1979, Nobel 2021): the spin glass order parameter is a function q(x) on [0,1] rather than a single value.
P(q) shows the overlap distribution between replicas. Full RSB → continuous q(x); k-RSB → k step function.