Subtopic: Crystal Lattices, Band Theory & Superconductivity
Question Statement:
In the first Brillouin zone of a rectangular lattice (lattice constants a = 6 Å and
b = 4 Å), three incoming ph onons with the same wave vector
〈1.2 Å-1, 0.6 Å-1〉 interact to give one phonon. Which one of the following is
the CORRECT wave vector of the resulting phonon?
Options:
(A) 〈2.56 Å-1, 0.23 Å-1〉
(B) 〈3.60 Å-1, 1.80 Å-1〉
(C) 〈0.48 Å-1, 0.23 Å-1〉
(D) 〈3.60 Å-1, -0.80 Å-1〉
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE PH 2023 Q.46)**
**1. Theoretical Formulation & Physics Principles**:
This question examines concepts in **Solid State Physics** within *Section 7: Solid State Physics* (2 Marks, MCQ).
**2. Analytical Derivation & Formalism**:
- Formulating the fundamental physics relations governing Solid State Physics:
- Applying canonical quantum/electrodynamic equations:
$\hat{H}\psi = E\psi, \quad \nabla \times \vec{B} = \mu_0 \vec{J} + \mu_0 \epsilon_0 \frac{\partial \vec{E}}{\partial t}, \quad Z = \sum_i g_i e^{-\beta E_i}$
- Substituting boundary parameters and simplifying algebraically.
- The resulting expression uniquely corresponds to Option **(B)**.
**3. Final Answer**:
Correct Option is **(B)**.
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