A symmetry formula for correlation functions in the superintegrable chiral Potts spin chain

We prove an exact finite-volume symmetry formula for two-point functions in the periodic $N$-state superintegrable chiral Potts spin chain. We show that, for every chain length $L$ and every simultaneous eigenvector of the Hamiltonian and the one-site translation operator, the correlations satisfy $⟨Z_0^r{Z}_R^{†r}{⟩}^{\ast }=⟨Z_0^r{Z}_{L-R}^{†r}⟩$ for $1⩽r⩽N-1$. Hence, whenever $L$ is even, the midpoint correlation $⟨Z_0^r{Z}_{L\mathrm{/}2}^{†r}⟩$ is real. Then we generalise the three-state chain case to arbitrary $N$ and to every translation eigensector. This resolves a conjecture of Fabricius and McCoy.