Spontaneous magnetization in the quantum Heisenberg ferromagnet

OpenAI

For the nearest-neighbor isotropic quantum Heisenberg ferromagnet on ℤᵈ with d≥3 and every positive half-integer spin S, a translation-invariant zero-field KMS equilibrium state exists at sufficiently low positive temperature with magnetization at least S/4.

Sources for this record

What was already known

Positive-temperature spontaneous magnetization for this standard quantum ferromagnet was a longstanding problem. Earlier spin-wave and other-model results did not establish this ordered equilibrium state.

AI involvement AI-led

OpenAI attributes the manuscript and Lean artifact to an internal model. The released record does not identify a human-origin central argument.

OpenAI attributes the research collection to an internal model; the record does not establish the low-human-input threshold for AI-autonomous on this particular theorem.

Importance Major

Would resolve the low-temperature ordered-state version of Lieb’s Problem A in every dimension at least three.

Limitations

The theorem concerns existence of an ordered KMS state, not the distinct finite-volume two-point formulation or companion Bloch-law results. No named human explanation of the ordered-state argument was found.

Technical verification Formal (Lean 4)

The released Lean scope note and OAI main proof identify an ordered translation-invariant KMS state at low temperature for nearest-neighbor models in every dimension at least three. Formal is source-reported for that scoped statement; it does not cover companion Bloch-law claims and no local build was performed.

Formal checking

The source reports a Lean proof of the low-temperature ordered-state theorem.

Checker
OpenAI Lean formalization
Scope
Nearest-neighbor d≥3, positive-spin low-temperature ordered KMS state with magnetization at least S/4
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Few

No named human explanation of the central ordered-state argument was found in the released material. Few is the evidence default.

Correction and publication history

2026-10-18 · publication

The result establishes a low-temperature ordered KMS state in the stated nearest-neighbor model.

Read this published revision