Editing Condensed matter physics (section)

==Experimental==
Experimental condensed matter physics involves the use of experimental probes to try to discover new properties of materials. Such probes include effects of [[electric field|electric]] and [[magnetic field]]s, measuring [[response function]]s, [[transport theory (statistical physics)|transport properties]] and [[thermometry]].<ref name=exptcm>{{cite book|last=Richardson|first=Robert C.|title=Experimental methods in Condensed Matter Physics at Low Temperatures|year=1988|publisher=Addison-Wesley|isbn=978-0-201-15002-5}}</ref> Commonly used experimental methods include [[spectroscopy]], with probes such as [[X-ray spectroscopy|X-rays]], [[infrared spectroscopy|infrared light]] and [[inelastic neutron scattering]]; study of thermal response, such as [[specific heat]] and measuring transport via thermal and heat [[conduction (heat)|conduction]].
[[File:Lysozym diffraction.png|thumb|upright|Image of X-ray diffraction pattern from a [[protein]] crystal]]

===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}}

===External magnetic fields===
In experimental condensed matter physics, external [[magnetic field]]s act as [[thermodynamic variable]]s that control the state, phase transitions and properties of material systems.<ref name=iupap-report>{{cite web |last=Committee on Facilities for Condensed Matter Physics|title=Report of the IUPAP working group on Facilities for Condensed Matter Physics : High Magnetic Fields |url=http://archive.iupap.org/wg/wg3/hmff/file_50963.pdf |publisher=International Union of Pure and Applied Physics|year=2004 |quote=The magnetic field is not simply a spectroscopic tool but a thermodynamic variable which, along with temperature and pressure, controls the state, the phase transitions and the properties of materials.|access-date=2016-02-07|archive-url=https://web.archive.org/web/20140222151520/http://www.iupap.org/wg/wg3/hmff/file_50963.pdf|archive-date=2014-02-22|url-status=dead }}</ref>  [[Nuclear magnetic resonance]] (NMR) is a method by which external [[magnetic fields]] are used to find resonance modes of individual nuclei, thus giving information about the atomic, molecular, and bond structure of their environment. NMR experiments can be made in magnetic fields with strengths up to 60 [[Tesla (unit)|tesla]].  Higher magnetic fields can improve the quality of NMR measurement data.<ref name="StatesAstronomy2013"/>{{rp|69}}<ref>{{cite book|title=High Magnetic Fields|chapter=Nuclear Magnetic Resonance in Solids at very high magnetic fields|author1=Moulton, W. G. |author2=Reyes, A. P. |editor=Herlach, Fritz |series=Science and Technology|publisher=World Scientific|year=2006|chapter-url=https://books.google.com/books?id=tN8CbCHzBmcC&pg=PA185|isbn=978-981-277-488-0}}</ref>{{rp|185}} [[Quantum oscillations]] is another experimental method where high magnetic fields are used to study material properties such as the geometry of the [[Fermi surface]].<ref name=doiron-leyraud2007>{{cite journal|last=Doiron-Leyraud|first=Nicolas|title=Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor|journal=Nature|year=2007|volume=447|pages=565–568|doi=10.1038/nature05872|arxiv= 0801.1281 |bibcode= 2007Natur.447..565D|issue=7144|pmid=17538614 |s2cid=4397560|display-authors=etal}}</ref>  High magnetic fields will be useful in experimental testing of the various theoretical predictions such as the quantized [[magnetoelectric effect]], image [[magnetic monopole]], and the half-integer [[quantum Hall effect]].<ref name="StatesAstronomy2013">{{cite book|author=Committee to Assess the Current Status and Future Direction of High Magnetic Field Science in the United States; Board on Physics and Astronomy; Division on Engineering and Physical Sciences; National Research Council|title=High Magnetic Field Science and Its Application in the United States: Current Status and Future Directions|url=http://www.nap.edu/catalog/18355/high-magnetic-field-science-and-its-application-in-the-united-states|date=25 November 2013|publisher=National Academies Press|isbn=978-0-309-28634-3|doi=10.17226/18355}}</ref>{{rp|57}}

===Magnetic resonance spectroscopy===
The [[local structure]], as well as the structure of the nearest neighbour atoms, can be investigated in condensed matter with magnetic resonance methods, such as [[electron paramagnetic resonance]] (EPR) and [[nuclear magnetic resonance]] (NMR), which are very sensitive to the details of the surrounding of nuclei and electrons by means of the  hyperfine coupling. Both localized electrons and specific stable or unstable isotopes of the [[Atomic nucleus|nuclei]] become the probe of these [[hyperfine structure|hyperfine interactions]]), which couple the electron or nuclear spin to the local  electric and magnetic fields. These methods are suitable to study defects, diffusion, phase transitions and magnetic order. Common experimental methods include [[nuclear magnetic resonance|NMR]], [[nuclear quadrupole resonance]] (NQR), implanted radioactive probes as in the case of [[muon spin spectroscopy]] (<math> \mu</math>SR), [[Mössbauer spectroscopy]], <math>\beta</math>NMR and [[perturbed angular correlation]] (PAC). PAC is especially ideal for the study of phase changes at extreme temperatures above 2000&nbsp;°C due to the temperature independence of the method.

===Cold atomic gases===
{{Main|Optical lattice}}

[[File:Bose Einstein condensate.png|thumb|left|The first [[Bose–Einstein condensate]] observed in a gas of ultracold [[rubidium]] atoms. The blue and white areas represent higher density.]]

[[Ultracold atom]] trapping in optical lattices is an experimental tool commonly used in condensed matter physics, and in [[atomic, molecular, and optical physics]]. The method involves using optical lasers to form an [[interference (wave propagation)|interference pattern]], which acts as a ''lattice'', in which ions or atoms can be placed at very low temperatures. Cold atoms in optical lattices are used as ''quantum simulators'', that is, they act as controllable systems that can model behavior of more complicated systems, such as [[Geometrical frustration|frustrated magnets]].<ref name=buluta-science2009>{{cite journal|last=Buluta|first=Iulia|author2=Nori, Franco|title=Quantum Simulators|journal=Science|year=2009|volume=326|issue=5949|doi=10.1126/science.1177838|bibcode= 2009Sci...326..108B|pages=108–11|pmid=19797653|s2cid=17187000}}</ref> In particular, they are used to engineer one-, two- and three-dimensional lattices for a [[Hubbard model]] with pre-specified parameters, and to study phase transitions for [[antiferromagnetism|antiferromagnetic]] and [[spin liquid]] ordering.<ref name=greiner-nature2008>{{cite journal |last=Greiner |first=Markus |author2=Fölling, Simon |title=Condensed-matter physics: Optical lattices |journal=Nature|year=2008|volume=453|pages=736–738|doi=10.1038/453736a|bibcode= 2008Natur.453..736G|issue=7196|pmid=18528388|s2cid=4572899 }}</ref><ref name=jaksch-aop2005>{{cite journal|last=Jaksch|first=D.|author2=Zoller, P. |title=The cold atom Hubbard toolbox|journal=Annals of Physics|year=2005|volume=315|issue=1|pages=52–79|doi=10.1016/j.aop.2004.09.010|arxiv= cond-mat/0410614 |bibcode= 2005AnPhy.315...52J|citeseerx=10.1.1.305.9031|s2cid=12352119}}</ref><ref name=":0" />

In 1995, a gas of [[rubidium]] atoms cooled down to a temperature of 170 [[Kelvin|nK]] was used to experimentally realize the [[Bose–Einstein condensate]], a novel state of matter originally predicted by [[S. N. Bose]] and [[Albert Einstein]], wherein a large number of atoms occupy one [[quantum state]].<ref name=nytimes-BEC>{{cite news|last=Glanz|first=James|title=3 Researchers Based in U.S. Win Nobel Prize in Physics|url=https://www.nytimes.com/2001/10/10/us/3-researchers-based-in-us-win-nobel-prize-in-physics.html|access-date=23 May 2012|newspaper=The New York Times|date=October 10, 2001}}</ref>