TY  - RPRT
TI  - Perturbation theory for Floquet eigenvalues in a zero-range potential.
AU  - G Alvarez
AU  - B Sundaram
PY  - 1990
DO  - 10.1103/physreva.42.452
UR  - https://pubmed.ncbi.nlm.nih.gov/9903822/
ID  - 9903822
ER  -