H. Schulz-Baldes, M. Zarrouati Rigorous spectral analysis of the metal-insulator transition in a limit-periodic potential (121K, Postscript) ABSTRACT. We consider the almost-periodic Jacobi matrices associated to the real Julia sets of $f_\lambda(z)=z^2-\lambda$ for which $\lambda\in [2,\infty)$ can be seen as the strength of the limit-periodic coefficients. The typical local spectral exponent of their spectral measures is shown to be a harmonic function in $\lambda$ decreasing logarithmically from $1$ to $0$.