I'm asked to prove that the condition for the existence of an energy gap at the boudnry of the Brillouin zone on a 1D lattice is equivalent to the condition for Bragg refraction. I don't understand this question. Doesn't an energy gap arise solely when there is a potential? Meanwhile, Bragg refraction only depends on the lattice structure, the potential is irrelevant. What am I missing here?(adsbygoogle = window.adsbygoogle || []).push({});

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# Energy gap and bragg refraction

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