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\title{Complete Solid State Physics: Reciprocal Lattice}
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\section{Reciprocal Lattice}

The reciprocal lattice is defined by vectors $\mathbf b_i$ satisfying

$$
\mathbf a_i\cdot \mathbf b_j=2\pi\delta_{ij}.
$$

Waves in a crystal are naturally organized by reciprocal vectors because
crystal momentum is conserved modulo a reciprocal lattice vector.

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