- D. I. Borisov, “Some singular perturbations of periodic operators”, Theor Math Phys, 151, № 2, 2007,
614 
- Tomáš Dohnal, Michael Plum, Wolfgang Reichel, “Localized Modes of the Linear Periodic Schrödinger Operator with a Nonlocal Perturbation”, SIAM J. Math. Anal., 41, № 5, 2009,
1967