solid-state physics

The branch of physics that deals with the physical properties of solid materials, especially the electromagnetic, thermodynamic, and structural properties of crystalline solids. Also called condensed matter physics.

The study of the physical properties of solids, such as electrical, dielectric, elastic, and thermal properties, and their understanding in terms of fundamental physical laws. Most problems in solid-state physics would be called solid-state chemistry if studied by scientists with chemical training, and vice versa. Solid-state physics emphasizes the properties common to large classes of compounds rather than the dependence of properties upon compositions, the latter receiving greater emphasis in solid-state chemistry. In addition, solid-state chemistry tends to be more descriptive, while solid-state physics focuses upon quantitative relationships between properties and the underlying electronic structure. See also Solid-state chemistry.

Many of the scientists who study the physics of liquids identify with solid-state physics, and the term “condensed-matter physics” has been used by some researchers to replace “solid-state physics” as a division of physics. It includes noncrystalline solids such as glass as well as crystalline solids. See also Amorphous solid; Glass.

In solid-state physics it is generally assumed that the electronic states can be described as wavelike. The individual electronic states, called Bloch states, have energies which depend upon the wave number (a vector equal to the momentum divided by ℏ, which is Planck's constant divided by 2π), and the wave number is restricted to a domain called the Brillouin zone. This energy given as a function of the wave number is called the band structure. There are several curves, called bands, for each line in the Brillouin zone. See also Brillouin zone.

The total energy of a solid includes a sum of the energies of the occupied electronic states. Since the energy bands depend upon the positions of the atoms, so does the total energy, and the stable crystal structure is that which minimizes this energy. The theory has not proved adequate to really predict the crystal structure of various solids, but it is possible to predict the changes in energy under various distortions of the lattice. There are in fact three times as many independent distortions, called normal modes, as there are atoms in the solid. Each has a wave number, and the frequencies of the normal vibrational modes, as a function of wave number in the Brillouin zone, form vibrational bands in direct analogy with the electronic energy bands. These can be directly calculated from quantum theory or measured by using neutron or x-ray diffraction. See also Crystal; Lattice vibrations; Neutron diffraction; X-ray diffraction.

For more information on solid-state physics, visit Britannica.com.

Solid-state physics, the largest branch of condensed matter physics, is the study of rigid matter, or solids. The bulk of solid-state physics theory and research is focused on crystals, largely because the periodicity of atoms in a crystal — its defining characteristic —facilitates mathematical modeling, and also because crystalline materials often have electrical, magnetic, optical, or mechanical properties that can be exploited for engineering purposes.

The framework of most solid-state physics theory is the Schrödinger (wave) formulation of non-relativistic quantum mechanics. Bloch's Theorem, which characterizes the wavefunctions of electrons in a periodic potential, is an important starting point for much analysis. Since Bloch's Theorem applies only to periodic potentials, and since unceasing random movements of atoms in a crystal disrupt periodicity, this use of Bloch's Theorem is only an approximation, but it has proven to be a tremendously valuable approximation, without which most solid-state physics analysis would be intractable. Deviations from periodicity are treated by quantum mechanical perturbation theory.

Topics

• Amorphous solid
• Crystal structure
  • defects
  • quasicrystal
  • Free electron model
  • reciprocal lattice
  • X-ray crystallography
  • neutron diffraction
  • dynamical theory of diffraction
• Electronic structure
  • bandgap
  • Bloch waves (electron waves in a lattice)
  • conduction band
  • effective mass
  • electron hole
  • Fermi gas
    • Fermi energy
  • Fermi liquid
  • exciton
  • valence band
• Electronic transport
  • Bloch oscillations
  • Drude model
  • electrical conduction
  • Hall effect
  • magnetoresistance
  • superconductivity
• Mechanical properties
  • Debye model of specific heat
  • elasticity
  • Mössbauer effect
  • phonons (lattice vibrations)
• Optical properties
  • crystal optics

See also

External links and references

• Online textbook: Introduction to Modern Solid State Physics by Yuri M. Galperin.

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Solid state physics

General subfields within physics
Classical mechanics · Electromagnetism · Thermodynamics · Statistical mechanics · Quantum mechanics · Relativity · High energy physics · Condensed matter physics · Atomic, molecular, and optical physics

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