Solution
= Solution
At large positive g, $\epsilon_k=2Jg-2J\cos k+O(J/g)$. The gap grows as $2J(g-1)$ while the leading bandwidth remains 4J. The field-polarized vacuum is unique.
= Solution
At large positive g, $\epsilon_k=2Jg-2J\cos k+O(J/g)$. The gap grows as $2J(g-1)$ while the leading bandwidth remains 4J. The field-polarized vacuum is unique.