What is special about ka=n? ?
What is special about ka=n? ?
This corresponds to electron wavelengths of 2a/n, or twice the lattice spacing coresponds to an integer multiple of the free particle wavelength, and a free particle with this wavelength would be reflected by the lattice.
This corresponds to the “stop bands” in a periodically loaded waveguide. The width of the stop band depends on the details of the interaction.