Quick and Dirty Preview of Solid State Physics
JHU Seal Quick and Dirty Preview of Solid State Physics

Jeffrey Wasserman
Second Year Seminar
Presented April 9, 2002
Johns Hopkins University

JHU Logo
Table of Contents

  1. Presentation Title
  2. What is Solid State Physics?
  3. What does Solid State Physics entail?
  4. Relative Importance of Solid State Physics
  5. Why is there interest in Solid State Physics?
  6. Historical Approach Part I - The Drude Model
  7. Successes of the Drude Model
  8. Historical Approach Part II - The Sommerfeld Model
  9. Inadequacies of the Drude and Sommerfeld Models
  10. Crystals and Lattices
  11. More About Lattices
  12. Reciprocal Lattice
  13. X-Ray Diffraction and Scattering from Lattices
  14. Effects of the Periodicity of the Lattice
  15. Bloch Waves and Brillouin Zones
  16. Brillouin Zones in Three Dimensions
  17. The Fermi Energy and the Fermi Surface
  18. The Nearly-Free Electron Gas
  19. Illustration of Nearly-Free Electron Gas in 1 Dimension
  20. Nearly-Free Electron Gas and Conductivity
  21. Nearly-Free Electron Gas in Aluminum
  22. Tightly-Bound Electrons - Overview
  23. Tightly-Bound Electrons and Band Structure
  24. Further Topics and Applications
Previous Slide Next Slide
Image 0
The previously-described band structure is important for determining the conductivity of the material. This is due to the Fermi energy and where it lies on the band structure.

At everyday temperatures, the Fermi level blurs a bit due to the Fermi-Dirac distribution, but the Fermi energy itself can typically be used to estimate the conductivity. For elements with an even number of valence electrons, the Fermi energy lies in the gap between energy bands. This implies that a significant amount of energy the size of the gap must be added to the system to insert another electron. This inserted electron would give rise to conductivity, but is difficult if it has to overcome the energy gap. These materials are insulators, because it requires significant energy to get a current flow.

However, materials with an odd number of valence electrons have the Fermi energy halfway in each band. That is, the Fermi energy does not lie in a gap. To insert another electron, only a small amount of energy is required, equal to the spacing between the quasi-continuous energy levels. These materials are conductors.

A third class of materials exists, which should be classified as insulators. However, the band gap is small enough that thermal excitation gives the electrons enough energy to jump the band, and they give rise to some current. These materials are semi-conductors.