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Topological characteristics of the spectrum of the Schrödinger operator in a magnetic field and in a weak potential
A. S. Lyskova
Abstract:
A study is made of the two-dimensional Schrödinger operator
$H$ in a periodic magnetic
field
$B(x,y)$ and in an electric field with periodic potential
$V(x,y)$. It is assumed
that the functions
$B(x,y)$ and
$V(x,y)$ are periodic with respect to some lattice
$\Gamma$
in
$R^2$ and that the magnetic flux through a unit cell is an integral number. The operator
$H$ is represented as a direct integral over the two-dimensional torus of the reciprocal
lattice of elliptic self-adjoint operators
$H_{p_1,p_2}$, which possess a discrete spectrum
$\lambda_j(p_1,p_2)$,
$j=0,1,2,\dots$. On the basis of an exactly integrable case – the Schrödinger operator in a constant magnetic field – perturbation theory is used to
investigate the typical dispersion laws
$\lambda_j(p_1,p_2)$ and establish their topological characteristics (quantum numbers). A theorem is proved: In the general case, the Schrödinger operator has a countable number of dispersion laws with arbitrary quantum numbers in no way related to one another or to the flux of the external magnetic field.
Received: 03.12.1984