Why Isn't Bloch's Theorem Reduced to Unity?

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SUMMARY

The discussion centers on Bloch's Theorem, which states that the wave function satisfies the equation \(\psi(\textbf{r}+\textbf{R})=e^{i\textbf{k}\cdot \textbf{R}}\psi(\textbf{r})\). The confusion arises regarding why this does not simplify to \(\psi(\textbf{r}+\textbf{R})=1\psi(\textbf{r})\) when \(\textbf{k}\) is a vector in the reciprocal lattice. It is established that \(\textbf{k}\) is not restricted to reciprocal lattice vectors, as it can represent a range of wave vectors, thus allowing for directional properties in wave functions.

PREREQUISITES
  • Understanding of Bloch's Theorem in solid-state physics
  • Familiarity with reciprocal lattice vectors
  • Knowledge of wave functions and their properties
  • Basic concepts of quantum mechanics and wave-particle duality
NEXT STEPS
  • Study the implications of Bloch's Theorem in solid-state physics
  • Explore the concept of reciprocal lattice and its significance in crystallography
  • Learn about the first Brillouin zone and its role in band theory
  • Investigate the relationship between wave vectors and wave function directionality
USEFUL FOR

Students and professionals in physics, particularly those focusing on solid-state physics, quantum mechanics, and materials science, will benefit from this discussion.

toqp
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This is not any homework problem but just something I don't understand. The Bloch theorem states that
\psi(\textbf{r}+\textbf{R})=e^{i\textbf{k}\cdot \textbf{R}}\psi(\textbf{r})

Now the k is a vector in the reciprocal lattice (usually in the first Brillouin zone), which is defined as the set of vectors K that satisfy
e^{i\textbf{K}\cdot\textbf{R}}=1

Now, if k points to a point in the reciprocal lattice, then why isn't the Bloch theorem
\psi(\textbf{r}+\textbf{R})=e^{i\textbf{k}\cdot \textbf{R}}\psi(\textbf{r})
just
\psi(\textbf{r}+\textbf{R})=1\psi(\textbf{r})?
 
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AFAIK, k is not limited to a reciprocal lattice vector. I think that would only be for standing waves. The complex phase gives the wave a direction.
 

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