Meromorphic continuations of finite gap Herglotz functions and periodic   Jacobi matrices
  We find a necessary and sufficient condition for a Herglotz function $m$ to be the Borel transform of the spectral measure of an exponentially decaying perturbation of a periodic Jacobi matrix. The condition is in terms of meromorphic continuation of $m$ to a natural Riemann surface and the structure of its zeros and poles.   The analogous result is also established for the Borel transform of the spectral measure of eventually periodic Jacobi matrices.   This paper generalizes the corresponding result from [17] for exponentially decaying perturbations of the free Jacobi matrix. 
Rostyslav Kozhan
math.SP math-ph math.MP