Editing Condensed matter physics (section)

===Scattering===
{{Further|Scattering}}

Several condensed matter experiments involve scattering of an experimental probe, such as [[X-ray]], optical [[photon]]s, [[neutron]]s, etc., on constituents of a material. The choice of scattering probe depends on the observation energy scale of interest. [[Visible light]] has energy on the scale of 1 [[electron volt]] (eV) and is used as a scattering probe to measure variations in material properties such as the [[dielectric constant]] and [[refractive index]]. X-rays have energies of the order of 10 [[electron volt|keV]] and hence are able to probe atomic length scales, and are used to measure variations in electron charge density and crystal structure.<ref name=chaikin-lubensky>{{cite book|last1=Chaikin|first1=P. M.|last2=Lubensky|first2=T. C.|title=Principles of condensed matter physics|year=1995|publisher=Cambridge University Press|isbn=978-0-521-43224-5|url-access=registration|url=https://archive.org/details/principlesofcond00chai}}</ref>{{rp|33–34}}

[[Neutron]]s can also probe atomic length scales and are used to study the scattering off nuclei and electron [[Spin (physics)|spins]] and magnetization (as neutrons have spin but no charge). Coulomb and [[Mott scattering]] measurements can be made by using [[electron beams]] as scattering probes.<ref name=chaikin-lubensky/>{{rp|33–34}}<ref name="Zhang2012">{{cite book|author=Wentao Zhang|title=Photoemission Spectroscopy on High Temperature Superconductor: A Study of Bi2Sr2CaCu2O8 by Laser-Based Angle-Resolved Photoemission|date=22 August 2012|publisher=Springer Science & Business Media|isbn=978-3-642-32472-7}}</ref>{{rp|39–43}}  Similarly, [[positron]] annihilation can be used as an indirect measurement of local electron density.<ref name=siegel-1980>{{cite journal|last=Siegel|first=R. W.|title=Positron Annihilation Spectroscopy|journal=[[Annual Review of Materials Science]]|year=1980|volume=10|pages=393–425|doi=10.1146/annurev.ms.10.080180.002141|bibcode= 1980AnRMS..10..393S}}</ref> [[Laser spectroscopy]] is an excellent tool for studying the microscopic properties of a medium, for example, to study [[forbidden transition]]s in media with [[non-linear optics|nonlinear optical spectroscopy]].<ref name=NRC1986/> {{rp|258–259}}