Klein paradox for bound states - A puzzling phenomenon

While Klein paradox is often encountered in the context of scattering of relativistic particles at a potential barrier, we presently discuss a puzzling situation that arises with the Klein-Gordon equation for bound states. With the usual minimal coupling procedure of introducing the interaction potential, a paradoxical situation arises when the 'hill' becomes a 'well', simulating a bound-state like situation. The phenomenal phenomenon for bound states is contrary to the conventional wisdom of quantum mechanics and is analogous to the well-known Klein paradox, a generic property of relativistic wave equations. PACs Nos. 03.65.Ge, 03.65.Pm