Definition
Umklapp scattering is a process in solid-state physics where the momentum of phonons (quanta of lattice vibrations) is not conserved within the original Brillouin zone, leading to thermal resistance in materials.
Etymology
The term "Umklapp" comes from the German word "umklappen," meaning "to flip over" or "to turn around," reflecting the momentum shift that occurs during the process.
Example usage
'The thermal conductivity of the crystal was reduced due to Umklapp scattering at higher temperatures.'
Interesting fact
Umklapp scattering is crucial in determining the thermal conductivity of materials, especially at high temperatures where it becomes the dominant scattering mechanism.
Source: Kittel, C. (2005). Introduction to Solid State Physics.
Explanation and detail
Phonons and Momentum Conservation
In a crystal lattice, heat is primarily transported by phonons. When phonons scatter, their momentum is typically conserved. However, in Umklapp processes, the phonon momentum is effectively flipped, transferring it to the lattice as a whole, thus appearing as a loss of momentum within the original Brillouin zone.
Impact on Thermal Conductivity
Umklapp scattering becomes significant at higher temperatures and limits the thermal conductivity of materials. This is because it disrupts the flow of phonons, which are essential for heat transfer. As a result, materials with high Umklapp scattering rates can be less efficient at conducting heat.
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