Solid state - Energy of electron in Brillouin zone

In summary, the energy of an electron in the second Brillouin zone can be less than the energy of an electron in the first zone due to the overlapping of bands in a simple cubic lattice and the difference in distance from the origin at different points in the Brillouin zone. This phenomenon occurs in any shape other than a sphere, which is not possible for the Brillouin zone.
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Homework Statement



Using geometrical arguments or otherwise, derive how the energy of an electron in the second Brillouin zone may be less than the energy of an electron in the first zone. [3]

Homework Equations





The Attempt at a Solution



I'm thinking this has something to do with overlapping bands, I think divalent metals show these characteristics. I'm not really sure where to start off from with a derivation though.
 
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Suppose we have a simple cubic lattice, whose 1st Brillouin zone (1BZ) is a cube. Let's consider a vertex and the center of a face on this cube.

We know the the distance of the vertex from the origin is sqrt(3) times that of the center of the face. Therefore, in the (nearly) free electron model, the energy at the vertex is bigger.

Now consider a point near the vertex but still inside 1BZ and a point near the center of a face but a little bit outside 1BZ. Which one has the bigger energy?

This kind of thing happens in any shape other than sphere, which is impossible to be the shape of the Brillouin zone.
 
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1. What is the Brillouin zone in solid state physics?

The Brillouin zone is a concept in solid state physics that describes the range of allowed electron energies in a crystal lattice. It is a mathematical construct that represents the repeating pattern of the crystal lattice in reciprocal space.

2. How does the energy of electrons in the Brillouin zone affect the behavior of a solid?

The energy of electrons in the Brillouin zone plays a crucial role in determining the electronic and optical properties of a solid material. It affects phenomena such as electrical conductivity, thermal conductivity, and the ability of a material to absorb or emit light.

3. What is the relationship between the Brillouin zone and band structure?

The Brillouin zone is intimately connected to the concept of band structure in solid state physics. The allowed electron energies in the Brillouin zone correspond to energy levels or bands in the electronic structure of a material. The band structure determines many of the material's properties and how it interacts with light and other forms of energy.

4. How is the Brillouin zone calculated or measured?

The Brillouin zone can be calculated from the crystal lattice parameters of a material using mathematical formulas. It can also be experimentally measured using techniques such as X-ray diffraction or electron diffraction. These methods allow scientists to visualize the repeating pattern of the crystal lattice in reciprocal space and determine the Brillouin zone.

5. What are some practical applications of understanding the energy of electrons in the Brillouin zone?

Understanding the energy of electrons in the Brillouin zone is essential for the development of new materials with specific properties. It is also crucial for the design and improvement of electronic and optoelectronic devices, such as transistors, solar cells, and LEDs. Additionally, this understanding can lead to advancements in fields such as energy storage and conversion, nanotechnology, and quantum computing.

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