Persistent currents for 2D Schr\"odinger operator with a strong   $\delta$-interaction on a loop
  We investigate the two-dimensional magnetic Schr\"odinger operator $H_{B,\beta}=(-i\nabla-A)^2 -\beta\delta(\cdot-\Gamma)$, where $\Gamma$ is a smooth loop and the vector potential $A$ corresponds to a homogeneous magnetic field $B$ perpendicular to the plane. The asymptotics of negative eigenvalues of $H_{B,\beta}$ for $\beta\to\infty$ is found. It shows, in particular, that for large enough positive $\beta$ the system exhibits persistent currents. 
Pavel Exner and Kazushi Yoshitomi