Jussi Behrndt, Pavel Exner, and Vladimir Lotoreichik
Schroedinger operators with delta-interactions supported on conical surfaces
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ABSTRACT.  We investigate the spectral properties of self-adjoint Schr\"odinger operators with attractive $\delta$-interactions of constant strength 
$lpha > 0$ supported on conical surfaces in $\mathbb{R}^3$. It is shown that the essential spectrum is given by $[-lpha^2/4,+\infty)$ and that the discrete spectrum is infinite and accumulates to $-lpha^2/4$. Furthermore, an asymptotic estimate of these eigenvalues is 
obtained.