Solid-state physics is the study of rigid , or s, through methods such as , , , and . It is the largest branch of . Solid-state physics studies how the large-scale properties of solid materials result from their ic-scale properties. Thus, solid-state physics forms a theoretical basis of . It also has direct applications, for example in the technology of s and s.


Solid materials are formed from densely packed atoms, which interact intensely. These interactions produce the mechanical (e.g. and ), , , and properties of solids. Depending on the material involved and the conditions in which it was formed, the atoms may be arranged in a regular, geometric pattern (, which include s and ordinary ) or irregularly (an such as common window ). The bulk of solid-state physics, as a general theory, is focused on s. Primarily, this is because the periodicity of s in a crystal — its defining characteristic — facilitates mathematical modeling. Likewise, crystalline materials often have , , , or properties that can be exploited for purposes. The forces between the atoms in a crystal can take a variety of forms. For example, in a crystal of (common salt), the crystal is made up of ic and , and held together with s. In others, the atoms share s and form s. In metals, electrons are shared amongst the whole crystal in ing. Finally, the noble gases do not undergo any of these types of bonding. In solid form, the noble gases are held together with s resulting from the polarisation of the electronic charge cloud on each atom. The differences between the types of solid result from the differences between their bonding.


The physical properties of solids have been common subjects of scientific inquiry for centuries, but a separate field going by the name of solid-state physics did not emerge until the 1940s, in particular with the establishment of the Division of Solid State Physics (DSSP) within the . The DSSP catered to industrial physicists, and solid-state physics became associated with the technological applications made possible by research on solids. By the early 1960s, the DSSP was the largest division of the American Physical Society. Large communities of solid state physicists also emerged in after , in particular in , , and the . In the United States and Europe, solid state became a prominent field through its investigations into semiconductors, superconductivity, nuclear magnetic resonance, and diverse other phenomena. During the early Cold War, research in solid state physics was often not restricted to solids, which led some physicists in the 1970s and 1980s to found the field of , which organized around common techniques used to investigate solids, liquids, plasmas, and other complex matter. Today, solid-state physics is broadly considered to be the subfield of condensed matter physics, often referred to as hard condensed matter, that focuses on the properties of solids with regular crystal lattices.

Crystal structure and properties

Many properties of materials are affected by their . This structure can be investigated using a range of techniques, including , and . The sizes of the individual crystals in a crystalline solid material vary depending on the material involved and the conditions when it was formed. Most crystalline materials encountered in everyday life are line, with the individual crystals being microscopic in scale, but macroscopic s can be produced either naturally (e.g. s) or artificially. Real crystals feature or irregularities in the ideal arrangements, and it is these defects that critically determine many of the electrical and mechanical properties of real materials.

Electronic properties

Properties of materials such as and are investigated by solid state physics. An early model of electrical conduction was the , which applied to the s in a solid. By assuming that the material contains immobile positive ions and an "electron gas" of classical, non-interacting electrons, the Drude model was able to explain electrical and and the in metals, although it greatly overestimated the electronic heat capacity. combined the classical Drude model with in the (or Drude-Sommerfeld model). Here, the electrons are modelled as a , a gas of particles which obey the quantum mechanical . The free electron model gave improved predictions for the heat capacity of metals, however, it was unable to explain the existence of . The is a modification of the free electron model which includes a weak periodic meant to model the interaction between the conduction electrons and the ions in a crystalline solid. By introducing the idea of , the theory explains the existence of , s and insulators. The nearly free electron model rewrites the for the case of a periodic . The solutions in this case are known as s. 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 .

Modern research

Modern research topics in solid-state physics include: * * s * * s * *

See also

* * *


Further reading

* and , ''Solid State Physics'' (Harcourt: Orlando, 1976). * , ' (Wiley: New York, 2004). * H. M. Rosenberg, ''The Solid State'' (Oxford University Press: Oxford, 1995). * , ''The Oxford Solid State Basics'' (Oxford University Press: Oxford, 2013). * ''Out of the Crystal Maze. Chapters from the History of Solid State Physics'', ed. Lillian Hoddeson, Ernest Braun, Jürgen Teichmann, Spencer Weart (Oxford: Oxford University Press, 1992). * M. A. Omar, ''Elementary Solid State Physics'' (Revised Printing, Addison-Wesley, 1993). * {{Authority control Metallurgy