Nonuniqueness for specifications in $\ell^{2+ε}$

For every $p>2$, we construct a regular and continuous specification ($g$-function), which has a variation sequence that is in $l^p$ and which admits multiple Gibbs measures. Combined with a recent result of Johansson and Oberg, this determines the optimal modulus of continuity for a specification which admits multiple Gibbs measures.