aka Sherington-Kirkpatrick model
Introduced in Solvable Model of a Spin-Glass, it is an infinite-range version of the EA Hamiltonian; equivalently a Spin glass in infinite dimensions. It's exact solution agrees with the Mean field theory solution. Note that the interactions are now between all pairs. The Hamiltonian is:
for a system of spins.
The Sherrington-Kirkpatrick model and its diluted version I - Dmitry Panchenko - Dmitry Panchenko
Solution via the Replica method
Phase transition
A Phase transition was found:
Negative entropy
if one chooses the EA order parameter to describe the broken symmetry of the low-temperature spin glass phase, the entropy becomes negative at very low temperature. This is problematic and is solved by the introduction of different order parameters, which cause Replica symmetry breaking.