Condensed matter

In the natural sciences, condensed matter denotes the solid and liquid state of aggregation in contrast to gas and plasma .

First Brillouin zone of an FCC grid

Condensed Matter Physics

The physics of condensed matter differs significantly from free particles ( elementary particle physics , atomic physics ) due to the mutual interaction of the building blocks of matter . Many phenomena such as deformability , magnetic order , or electrical conductivity can be traced back to a certain order of interaction between the building blocks of condensed matter. They are therefore to be treated very differently in condensed matter than in free particles, or they only appear in condensed matter.

The treatment of the physics of condensed matter is characterized by the fact that the large number of particles that form the system to be described excludes an elementary solution of the individual equations of motion. Instead of a description of the states of the individual particles of the system, statements about frequencies (or normalized to the number of possible states: probabilities) with which certain states of any particles in the system occur.

The general, microscopic description is based on the many-particle theory , which also takes particle interactions into account. For most applications, however, a description within the framework of the theory of the mean field is sufficient, in which all particles move independently of one another in an averaged, effective potential. Representatives of the latter are the Hartree-Fock method and density functional theory with the help of which, for example, a large number of material parameters can be obtained. With the material data obtained, the system can be treated with the help of classical field equations , taking macroscopic system properties such as system geometry and external loads into account . For example, elastic deformations in macroscopic continuum mechanics are calculated using the modulus of elasticity and Poisson's number . If, however, there are significant correlations between the particles in solids (for example long-range correlation of the atomic positions themselves crystal lattices, or correlation of the electron spins → magnetic order such as ferromagnetism and antiferromagnetism ), the description can no longer be made in the approximation of independent particles. The tools of many-body theory must then be used. ${\ displaystyle \ Rightarrow}$

The concepts of condensed matter physics are applied far beyond the area of solid and liquid matter (examples: risk management , insurance statistics , neural networks ).

Subject areas

Solid state physics

Crystalline silicon carbide

The solid-state physics deals with the physics of matter in the solid state of aggregation . Crystalline solids are of particular importance, i.e. those that have a translationally symmetrical (periodic) structure , as this translational symmetry drastically simplifies the treatment of many physical phenomena or even makes it possible in the first place.

Physics of liquids

The physics of liquids deals with matter in its liquid state. The building blocks of the liquid show a high degree of mutual mobility ( translation and rotation ).

Soft condensed matter

Polarization micrograph of a liquid crystal

The term soft condensed matter is used to summarize substances that differ from the "hard matter" of crystalline solids by two essential features:

On the one hand, the characteristic length scale is in the range of molecules, i.e. in a range between 1 nm and 1 µm. The basic building blocks of soft matter therefore have a complex substructure.
On the other hand, these building blocks are subject to strong thermal fluctuations, so that the relevant energy scale is set by the thermal excitation energy . The energies occurring here are therefore considerably smaller (typically a few meV) than in hard matter, where they are in the range of a few electron volts (eV). ${\ displaystyle k _ {\ mathrm {B}} T}$

Soft matter mainly includes amorphous substances that do not have a long-range crystalline order, such as: polymers , liquid crystals , colloids and membranes .

Systems (exemplary)

Wafer of silicon - bedeutendster today Semiconductors

Phenomena (exemplary)

A magnet hovers over a high-temperature superconductor (approx. −197 ° C) cooled with liquid nitrogen.

literature

Ch. Kittel : Introduction to Solid State Physics . 14th edition. R. Oldenbourg, Munich 2005, ISBN 3-486-57723-9 .
NW Ashcroft , ND Mermin : Solid State Physics . 3. Edition. R. Oldenbourg Wissenschaftsverlag, Munich 2007, ISBN 978-3-486-58273-4 .
H. Ibach, H. Lüth: Solid State Physics . 6th edition. Springer, Berlin 2002, ISBN 3-540-42738-4 .
K. Kopitzki, P. Herzog: Introduction to solid state physics . Teubner Verlag, ISBN 978-3-8351-0144-9 .
G. Czycholl: Theoretical solid state physics . Springer, ISBN 978-3-540-74789-5 .
Siegfried Hunklinger: Solid State Physics . 3rd, improved and updated edition. Oldenbourg Wissenschaftsverlag, Munich 2011, ISBN 978-3-486-70547-8 .
Rudolf Gross, Achim Marx: Solid State Physics . Oldenbourg Wissenschaftsverlag, Munich 2012, ISBN 978-3-486-71294-0 .

Web links

Britney's Guide to Semiconductor Physics (English)