The fundamental gap for a one-dimensional Schrödinger operator with Robin boundary conditions
Ben Andrews, Julie Clutterbuck, Daniel Hauer · Proceedings of the American Mathematical Society · 2020
For Schrödinger operators on an interval with either convex or symmetric single-well potentials and Robin or Neumann boundary conditions, the gap between the two lowest eigenvalues is minimized when the potential is constant. We also have results for the p p -Laplacian.