A vanishing theorem in $K$-theory for spectral projections of a non-periodic magnetic Schrödinger operator
We consider the Schrödinger operator $H(μ) = \nabla_{\bf A}^*\nabla_{\bf A} + μV$ on a Riemannian manifold $M$ of bounded geometry, where $μ>0$ is a coupling parameter, the magnetic field ${\bf B}=d{\bf A}$ and the electric potential $V$ are uniformly $C^\infty$-bounded, $V\geq 0$. We assume that, for some $E_0>0$, each connected component of the sublevel set $\{V<E_0\}$ of the potential $V$ is relatively compact. Under some assumptions on geometric and spectral properties of the connected components, we show that, for sufficiently large $μ$, the spectrum of $H(μ)$ in the interval $[0,E_0μ]$ has a gap, the spectral projection of $H(μ)$, corresponding to the interval $(-\infty,λ]$ with $λ$ in the gap, belongs to the Roe $C^*$-algebra $C^*(M)$ of the manifold $M$, and, if $M$ is not compact, its class in the $K$ theory of $C^*(M)$ is trivial.