Spectral asymptotics of all the eigenvalues of Schrödinger operators on flat tori

Abstract We study Schrodinger operators with Floquet boundary conditions on flat tori obtaining a spectral result giving an asymptotic expansion of all the eigenvalues. The expansion is in λ − δ with δ ∈ ( 0 , 1 ) for most of the eigenvalues λ (stable eigenvalues), while it is a “directional expansion” for the remaining eigenvalues (unstable eigenvalues). The proof is based on a structure theorem which is a variant of the one proved in [31] , [32] and on a new iterative quasimode argument.