Abstract:
Under consideration is a Hamiltonian $H$ describing the motion of a quantum particle on a $d$-mentional lattice in an exterior field. It is proven that if $H$ has an eigenvalue at the lower bound of its spectrum then this eigenvalue is nondegenerate and the corresponding eigenfunction is strictly positive (thereby a lattice analog of the Perron–Frobenius theorem is proven).
Key words:spectral properties, one-particle Hamiltonian on a lattice, Birman–Schwinger principle, eigenvalue, strictly positive function.