Condensed matter physics is a researchCondensed matterCorporealphysical propertyAndMicrostructureAnd the relationship between them, that is, by studying theElectronics、Ions、atomandmoleculeTo understand its physical properties.Condensed matter physics is one of the largest and most important branches of physics today.On the one hand, it is the outward extension of solid physics, which makes the research object include many liquid substances besides solid substances, such asliquid helium、Molten salt、liquid metal, andliquid crystal、latexAndpolymerAnd even some special gaseous substances, such asBose Einstein condensationBose gas and quantum degeneratefermi gas 。On the other hand, it also introduces newConceptual systemIt is not only conducive to dealing with many difficult problems left over by traditional solid physics, but also easy to be popularized and applied to some more difficult problemssolidMore complex substances.Historically, solid physics was founded in the 1930s and 1940s, while the name of condensed matter physics first appeared in the 1970s. In the 1980s and 1990s, it gradually replaced solid physics as a discipline name, or understood solid physics as a synonym of condensed matter physics.[1]
Condensed matter physics is todayphysicsOne of the largest and most important branch disciplines.Its research level is frommacroscopic、mesoscopic reachmicrocosmicTo further understand all kinds of condensed matter physical phenomena from the microscopic level;Material dimension fromthree-dimensionalTo low peacekeepingFractional dimension；Structure from cycle toAperiodicAnd quasi cycle, complete to incomplete and near complete;The external environment, from conventional conditions to extreme conditions and the interaction of various extreme conditions, has formed a more profound and universal theoretical system than solid state physics.After more than half a century of development, condensed matter physics has becomephysicsThe most important, rich and active discipline insemiconductor、magnetism、SuperconductorAnd other major achievements in many disciplines have played a key role in the field of modern high-tech science and technologyNew materialsNew devices and new processes provide a scientific basis.One of the important characteristics of condensed matter physics is the endless hot research topics and emerging interdisciplinary disciplines;Another important feature is its close connection with production practice. Many research topics often have bothfundamental researchWith the nature of development and application research, research results are expected to be rapidly transformed into productivity.
Origin and development
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Condensed matter physics originated from solid state physics andCryophysicsDevelopment of.In the 19th century, people gradually deepened their understanding of crystals.French physicist A in 1840·Bravais All 14 arrangements of three-dimensional crystals are derived, namelyBrave lattice。In 1912, German physicist Feng·LaueFoundX-rayCrystallinediffraction, creating a new era of solid state physics. Since then, people canDiffraction fringeStudy the microstructure of crystals.
In the 19th century, Britain was famousphysical scientistFaradayAt low temperatureliquefactionMost of the gases known at that time.In 1908, Dutch physicist H·Onnes Put the last gas that is difficult to liquefyheliumLiquefaction has created a new record of artificial low temperature - 269 ° C (4K), and found thatSuperconductivity phenomenon。superconductivityIt has broad application prospects. The theoretical and experimental research of superconductivity has made great progress in the 20th century. The record of the highest critical transition temperature has been constantly refreshed. The research of superconductivity has become one of the most popular fields in condensed matter physics.
L.Landau1937 forSecond-order phase transitionProposedSymmetry breakingLater, it became the main axis of the concept system of condensed matter physics.In a particularState of matterOne ofSymmetrical elementThere can be no ambiguity about the existence of.When a symmetrical element in the original phase changes temperature orTransformerThe sudden loss in the process means that the phase transition and the ordered phase have occurred.introduceOrder parameterUsed for qualitative andrationTo describe the deviation between the ordered phase and the original phase.When the temperature drops to zero (0K), the ordered phase reachesground stateInstead of the ordered phase at zero temperatureexcited state。But the excited state has recovered and brokenSymmetryThe tendency of.The low-energy excited state is nonlocalQuasiparticleIs calledMeta excitationCollection of.NonlinearThe localized excitation state is called "Chenwei" topological defect.Both elementary excitations and topological defects will affect different physical properties.[1]
When the material is at high enough temperatureGaseous, which is uniform andIsotropyIn terms of statistical significance, thetranslationandRotational symmetry, and the ones that govern itLaws of physicsThe symmetry of is the same.Cooling will make the gascoagulationAs a liquid, although the overall symmetry remains unchangedShort program。Cool down again and make the liquidfreezingAs a crystal, the symmetry of translation and rotation is broken, and the remaining symmetry belongs to 230Space groupOne of.Solid colorfulPhysical propertiesYes andSymmetry breakingClosely related, and most of the liquids with attractive physical properties areliquid crystalOr complex liquid, also related to some symmetry breaking.Crystalline stateThe meta excitations in areLattice vibrationorphonon, is the key to understanding the thermal properties of solids,Crystalline stateThe topology defect in isdislocation, is to understand the solidplasticityAnd strength.[1]
research contents
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The basic task of condensed matter physics is to clarifyMicrostructureAndPhysical propertiesSo as to judge some types of condensed matterMicroparticleWhether the collective of（Wave particle duality）It is of the utmost importance.Low electronic mass,normal atmospheric temperatureIt obviously presents quantum characteristics;The ions or atoms are heavy, and onlyliquid heliumOr at very low temperature (μ K to nK)alkali metalThe quantum characteristics of atoms are highlighted only when the gas is thin.This also explains why the low temperature condition is very important for the study of condensed matter physics.MicroparticleIt is divided into two categories: one isFermion, with half integerspin, obeyPauli exclusion principle；The other isBoson, with integerspin, the sameEnergy stateAllow any number of particles to occupy.The physical behavior of these two kinds of particles is quite different.[1]
Solid electron theory
The study of electronic behavior in solids has always been the core issue of solid state physics.This is still the case in condensed matter physics.The behavior of electrons in solids can be divided into three regions according to the interaction between electrons.[1]
① Weak correlation area.Based on electronic receivinglatticeSuperscatteredEnergy band theory, which provides a suitable theoretical framework for the electronic behavior in solids. It has been applied to semiconductors and simple metals with extraordinary success, and also forms the theoretical basis of semiconductor physics.[1]
② Medium correlation area.Including general metal and strongMagnetic material。Landau's Fermi liquid theory successfully describes general metals andthreeHe in liquidMeta excitationAnd physical behavior.W. Developed by Cohen and othersdensity functional theory It provides efficient and complex computingStructural materialsThe theoretical framework of the electronic structure in.The exchange interaction between electrons (including direct, indirect, super exchange, double exchange and itinerant exchange) leads to the magnetic ordered phase（Ferromagnet, antiferromagnet and more ferromagnet).Excited States of Magnetic Ordered Phase（MagnonAndMagnetic domain）It also provides an understanding of its physical parameters andMagnetization curveThe physical basis of ferromagnetism is formed by the opportunity of ".".[1]
③ Strong correlation area.Bad metals with very low electron concentration are involved.The energy band theory was established soon, EWignerIt is assumed that the Coulomb repulsion force makes the electrons localized on the Wigner lattice, and then N. Mott thinks that NiO and other oxides are caused by correlationinsulator, i.e. Motel insulator.1960sKondo ChunFor diluted magnetic alloyresistanceThe minimum phenomenon is theoretically explained asKondo effect。In the 1980s and 1990s, strange physical properties were found in a series of doped Mott insulators, such asCopper oxideFound inHigh temperature superconductor, manganese oxideGiant magnetoresistance effectEtc.In addition, it is also related to the Kondo effectLanthanideandActinide seriesMany ordered phases and abnormal physical properties have been found in heavy electron alloys.The research on the physical properties of the above kinds of strongly related substances has not yet been satisfactorily solved.[1]
Macroscopic quantum state
CryophysicsThe major achievement of the research is the discovery of superconductivity in metals and alloys (resistanceTcThe following sudden drop is zero,fluxAll are repelled and become completely diamagnetic) andSuperfluid phenomenon（Viscosity coefficientstayTcThe following sudden drop is zero).The appearance of these macroscopic quantum state phenomena isGauge symmetry（wave functionPhase can be any value).As early as 1924EinsteinAccording toBose Einstein statisticsProposedBose Einstein condensationThe assumption that the ideal Bose gas will appear at low temperatureground stateMacroNumber of particles%.fourHe atom is a boson, sofourHeSuperfluidAfter discovery, F. London proposedSuperfluid stateIt is the result of Bose Einstein condensation.The description of superconductivity proposed by LondonelectrodynamicsOfLondon equationIt actually containsMacroscopic quantum stateThe concept of.1952 VGinzburg And the phenomenology proposed by L. LandauSuperconductivity theoryThe complex order parameter similar to the macro wave function is explicitly introduced to describeSuperconductive state。1957 JBadinAnd put forward the correctSuperconducting microscopic theory, i.eBCS theoryThe key is that a pair of electrons in momentum spaceElectron phonon interactionAnd formedCooper Yes, so thatElectronic systemIt also has some characteristics similar to boson system.In 1972, it was found below 2.7mKthreeHe superfluid state,threeHe atom is also a fermion, so this is alsoFermionPairing results.From the symmetry of the order parameter, we can judge the characteristics of the paired state:Conventional superconductorIs the spin singlet of s wave pairing,High temperature superconductorIs the spin singlet of d-wave pairing,threeHeSuperfluidIt is a p-wave paired spin tristate with magnetism.There are also some suspected p-wave pairingUnconventional superconductor, under study.The mechanism of unconventional superconductors has yet to be clarified.In 1995, E. Konar et aleighty-sevenRb gas is cooled to extremely low temperature (μ K) to realize Bose Einstein condensation, which extends the research field of condensed matter physics to rarefied gas at extremely low temperature.[1]
Nanostructure and Mesoscopic Physics
Since the physical properties of some simple materials have been relatively clear, since the middle of the 20th century, efforts have been made to classify different materials according to specific structural dimensions (related to a certain physical propertyFeature length）To organize materials and devicescomplexSo as to obtain excellentphysical property 。If the selected structure size is within the nanometer range (1-100 nm), it isnanostructure。At the end of the 20th century, this field has aroused widespread attention in academia and society.[1]
quantum mechanicsThink particles can pass through nanoscalebarrierAnd presentTunnel effect。Using this effect, tunnel junctions such asSandwich structure, such as semiconductorTunnel diode, single electron superconducting tunnel junctionCooper YesSuperconducting tunnel junction.The latter embodiesJosephson effectHas becomeSuperconducting electronicsThe core device of.Using the spin dependent tunneling effect, a magnetic memory with tunneling magnetoresistance has been fabricated.[1]
nanostructurestayfundamental researchIt also played a very important role: integer and fraction were found in two-dimensional electron gasquantum hall effect As well as Wigner lattice, Luttinger liquid theory was verified in one-dimensional conductor, and mesoscopic quantum transport phenomenon was found in some artificial nanostructures.[1]
Soft Matter Physics
Soft matterAlso called complex liquid, it is between solid and liquidPhase，liquid crystal、latex、polymerAnd so on.Most soft materials areOrganic matterAlthough it is disordered on the atomic scaleMesoscopic scaleOn the other hand, there may be some regular and orderly structure.For example, the liquid crystal molecule is rod like, although its center of mass does not have position order, the orientation of the rod may be ordered.Another example is that the polymer is composed of soft long-chain molecules. Due to the relevance of long-range disorder, it follows a similarCritical phenomenonOfScaling law。The establishment of liquid crystal physics and polymer physics in the 1970s and 1980s successfully extended condensed matter physics from traditional hard matter to soft matter.Soft substances are exposed to small external stimuli (temperature, external field orexternal force）Its physical property is characterized by its remarkable response, thus producing obvious practical effects.OneThe button batteryDriveableLCD watchA few years is proof.In the process of changing soft matter, the internal energy changes very little, and the change of entropy is very significant, so the change of its organizational structure is mainly driven by entropy, which is quite different from the hard matter driven by internal energy.Entropy induced order and entropy induced deformation are soft matterSelf assemblyThe physical basis of.[1]
Organic matter（Small moleculeandpolymer）The electronic structure and electronic properties have also received extensive attention.Organic light-emitting devices and electronic devices are under development.[1]
The theoretical basis of condensed matter physics isquantum mechanics, basically complete and mature.However, due to the large number oftwenty-three）MicroparticleAnd the research objects are further complicated, new structures, new phenomena and new mechanisms are still emerging in endlessly, which need to be explored from experiments, theories and calculations, and still pose a strong challenge to human intelligence.[1]
Condensed matter physics is closely related to the development of high and new technology.Information, materials andEnergy technologyThe challenges faced in the 21st century will provide opportunities for the further development of condensed matter physics.Condensed matter physics still existsInterdisciplinaryThere is much to be done.With the development of condensed matter physics, materials with complex structures have been increasingly involved.The cross penetration between it and chemistry has become more and more obvious, and even the boundaries between disciplines have become blurred.It andbiologyThe cross penetration between them is also changing with each passing day, which includes mutual support in experimental technology and joint exploration in mechanism and theory.[1]
