coefficient is always larger than zero, and approaches 1 as the potential step goes to infinity. The Klein zone If the energy of the particle is in the range , then partial reflection rather than total reflection will result. Resolutions for the massive case While the traditional resolution uses particle–anti-particle pair production in the context of quantum field theory (Hansen 1981), a simpler resolution exists that substitutes physical pair production for the scattering of negative energy solutions under the barrier (Alhaidari 2009). This strategy was also applied to obtain analytic solutions to the Dirac equation for an infinite square well. Other cases These results were expanded to higher dimensions, and to other types of potentials, such as a linear step, a square barrier, a smooth potential, etc. Many experiments in electron transport in graphene rely on the Klein paradox for massless particles. See also List of paradoxes References Further reading Physical paradoxes