Související znalosti
Theso-calledlowtemperatureusuallymeanslowerthanthetemperatureofliquidnitrogen(77K),andmoreimportantlowtemperaturephenomenaoccurbelowthetemperatureofliquidhelium(4.2K).Thetechnologyofliquefyingair,hydrogenandheliumgas,aswellasthedevelopmentofvariousultra-lowtemperaturetechnologies(seeultra-lowtemperaturetechnology),hasenabledpeopletoobtainextremelylowtemperatureandultra-lowtemperatureexperimentalconditions.Atlowtemperatures,thethermal,electricalandmagneticpropertiesofmatterwillchangedrastically.Forexample,thespecificheatcapacityofasolidwillchangeabruptlyatcertaintemperatures;atasufficientlylowtemperature,inprinciple,allparamagneticmaterialscanexhibitferromagneticorantiferromagneticproperties(seemagneticmedia);theconductivityofmetalsissignificantlyimproved,whilethoseofsemiconductorsTheconductivityisgreatlyreduced.Thesephenomenaareallrelatedtoquantummechanicaleffectsatlowtemperatures.
Předmět historie a aktuální situace
In1908,H.Kamerlin-Onnessrealizedtheliquefactionofheliumforthefirsttime.Whenthetemperatureofliquidheliumislowerthantheentrypoint,itwillchangefromtheHeⅠphasetotheHeⅡphase.TheHeⅡphasehassuperfluidity,theviscositycoefficientbecomeszero,anditcanpassthroughthecapillaryunimpeded.Atthesametime,itsthermalconductivityisgreatlyincreased,whichisaboutabovetheentrypoint.3×106timesthetemperature.In1911,Onnesdiscoveredforthefirsttimethatsomemetalsexhibitzeroresistanceatextremelylowtemperatures,whichiscalledsuperconductivity.In1933,W.Meissnerdiscoveredthatsuperconductorsarecompletelydiamagnetic,andthemagneticfieldinthebodyisalwayszero(seesuperconductivity).Inaddition,thespecificheatcapacityofthesuperconductorhasasuddenchangeatthesuperconductingcriticaltemperature,andthereisnothermoelectricphenomenoninthesuperconductingstate,andsoon.Thesebizarrephenomenaofsuperfluidityandsuperconductorsarecloselyrelatedtomacroscopicquantumphenomenaatlowtemperatures,andtheyalloriginatefromsomesortoforderlytransformationthatoccursatlowtemperatures.Theresearchonsuperfluidityandsuperconductivityhasgreatlydeepenedpeople'sunderstandingofthelawsofthematerialworld,soithasalwaysbeenthefocusoflow-temperaturephysicsresearch.Researchonthepropertiesofliquid3Heand4Hehasledtotheemergenceofnewrefrigerationmethods(dilutedrefrigerators).Thestudyofvariouspropertiesandapplicationsofsuperconductorshasformedthesub-disciplineofsuperconductivityphysics.TheresearchandapplicationofsuperconductingdevicesbasedontheJosephsoneffecthasformedanewdisciplineofsuperconductingelectronics.After1986,theresearchandexplorationofhighcriticaltemperaturesuperconductingmaterialsshowedbroadprospectsforsuperconductingapplications.
Physicistsareconstantlylookingforsuperconductingmaterialswithhighercriticaltransitiontemperatures,andthehigh-temperaturesuperconductivityrecordisconstantlybeingrefreshed.Atpresent,high-temperaturesuperconductivityhasbecomeoneofthemostpopularresearchfieldsincondensedmatterphysics.