A boundary-singular two-dimensional partial data inverse problem

Abstract: We consider uniqueness in an inverse Schr\"odinger problem in a bounded domain in $\mathbb{R}^2$ given the Dirichlet-to-Neumann map on part of the boundary. On the remaining boundary we impose a new type of singular boundary condition with unknown parameter. Owing to recent results on this class of boundary conditions, we discuss the necessity of an extra point condition to well-define the data for the inverse problem. Our results are two-fold. At a single frequency the inverse problem displays non-uniqueness, since an unknown boundary condition can spoil `seeing' the Schr\"odinger potential via the Dirichlet-to-Neumann map. On the other hand, taking as input data the Dirichlet-to-Neumann map at every frequency $\lambda\in\mathbb{R}$ for which it is well-defined yields full uniqueness of the potential and all the boundary conditions. We adapt recent methods in related two-dimensional inverse problems and develop new techniques to cope with the singularity in the boundary condition.