Contents - Max-Planck-Institut für Physik komplexer Systeme
Contents - Max-Planck-Institut für Physik komplexer Systeme
Contents - Max-Planck-Institut für Physik komplexer Systeme
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Onthistopic,wecollaboratewiththegroupofErikLefebvre(CEA/DAM,Arpajon,France)andVladimir<br />
Tikhonchuk(CELIA,Bordeaux, France). Theexperimentalinvestigationofionaccelerationandits<br />
applications(e.g.,toprotonradiographyinplasmaexperiments)isdoneincollaborationwiththegroup<br />
ofJulienFuchs(LULI,Palaiseau,France). CollaborationwithRolandSauerbreyandUlrichSchramm<br />
(ForschungszentrumDresdenRossendorf)isalsoacknowledged.<br />
Jointresearchprogram mpipksandMPI-CPfS<br />
Overthepastdecade,anumberofemergentphasesinelectronicsystemshavebeenthesubjectof<br />
combinedexperimentalandtheoreticalinterest. Thesenovelphasesultimatelyarisefromthestrong<br />
Coulombrepulsionbetweenelectronsandtheinterplaybetweenitinerantandlocaldegreesoffreedom.As<br />
aresult,thewayamanyparticlesystemcanevolvefromonephasetoanotherhasattractedconsiderable<br />
attentionasanewparadigmforaddressingtheuniversalfeaturesofcorrelatedquantumsystems. The<br />
jointresearchgroupofthe mpipksandtheMPI-CPfScombinestheexpertiseinExperimentalsolidstate<br />
physicsandchemicalmetalsscienceoftheMPI-CPfSwiththoseontheoreticalquantummanyparticle<br />
physicsofthecondensedmatterresearchfieldof mpipkstoaddresstheseuniversalfeatures.Thegroup<br />
ofDr.StefanKirchner,“CollectivePhenomenainSolidStateandMaterialsScience“,islocatedatboth<br />
institutes.Itwasstartedin2009andisinvolvedinresearchonboththetheoreticalandtheexperimental<br />
aspectsofthisresearchprogram.Jointseminarsbetweenthetwoinstitutesfeaturetheoristsworkingin<br />
thebroadareaofstronglycorrelatedelectronphysics,superconductivityandmagnetism.<br />
JuniorResearchGroup:CollectivePhenomenainSolidStateandMaterialScience<br />
(Head:Dr.StefanKirchner)<br />
Thejointjuniorresearchgroupofthe<strong>Max</strong><strong>Planck</strong><strong>Institut</strong>esforthePhysicsofComplexSystemsand<br />
forChemicalPhysicsofSolidsbeganitsworkinFebruary2009.Researchinterestsofthegroupcenter<br />
aroundstronglycorrelatedelectronsystemswithacurrentemphasisonquantumcriticalityinrareearth<br />
intermetalliccompounds.<br />
Phasetransitionsconnectdifferentstatesofmatterandareubiquitous. Ifthetemperaturevanishesat<br />
whichthetransitionoccurs,aquantumphasetransitiontakesplace.Suchatransitioncanbecontinuous<br />
ordiscontinuousdependingonwhethertheorderparameterthatcharacterizesthephasetransitionis<br />
continuousornot.Quantumcriticalityoccursasmatteristunedthroughacontinuouszero-temperature<br />
phasetransitionandisfoundtoaffectthepropertiesofmatterinawidetemperatureandparameterrange<br />
fanningoutfromthezero-temperaturecriticalpoint. Sofar,theexistenceofquantumcriticalpoints<br />
hasbeenestablishedbeyondreasonabledoubtonlyinheavyfermionsystemsalthoughgrowingevidence<br />
existsthatquantumcriticalityalsogovernsthephasediagramofotherstronglycorrelatedmaterials,like<br />
e.g. thehigh-temperaturecupratesuperconductors. Inthetraditionalapproachtoquantumcriticality,<br />
thecriticalregimeisdescribedintermsofaGinzburg-Landau-Wilsonfunctionaloftheorderparameter<br />
anditsfluctuationswheretheorderparameterisaphysicalquantitycharacterizingtheorderedsideof<br />
thecriticalpoint. Quantummechanicsentersinthisapproachonlyinincreasingtheeffectivespatial<br />
dimensionsinwhichtheGinzburg-Landau-Wilsonfunctionalisdefined.Asaresult,thisclassicaltheory<br />
inelevateddimensionspredictsmeanfieldbehaviorformanysystems. Inthecontextofmagnetic<br />
quantumcriticality,theclassicalGinzburg-Landau-Wilsonapproachisknownasthespin-densitywave<br />
theory.Experimentalandtheoreticalworkforheavyfermionsystemshasestablishedtheexistenceofat<br />
leastoneotherclassofquantumcriticalpoints. Thisadditionalclassofquantumcriticalpointsdefies<br />
adescriptionintermsofaGinzburg-Landau-Wilsonfunctional. Characteristictoallquantumcritical<br />
pointsisthedivergingcorrelationlengthascriticalityisapproached. Thisdivergenceisattheheartof<br />
thescale-invariantenergyspectrumandtheoriginof’universality’i.e. thephenomenonthatthepower<br />
lawdivergenceofphysicalquantitiesislargelyindependentofphysicaldetailsofthesystem.Atpresent,<br />
neitherafieldtheoreticformulationforthenewclassofquantumcriticalpointsisknownnorageneral<br />
classificationofquantumcriticalpointsintouniversalityclassesisavailable.<br />
Thelackofanyintrinsicscaleatcriticalitysuggeststhatquantumcriticalpointsareparticularlysusceptible<br />
toexternalperturbationsasanyperturbationhastobeconsideredlargecomparedtothe(vanishing)<br />
intrinsicscales. Thus,understandingtheeffectsofnon-equilibriumcorrelationsnearquantumphase<br />
transitionsseemsofeminentpracticalrelevancewithrespecttoguidanceofexperimentalworksince<br />
28 ScientificWorkanditsOrganizationatthe<strong>Institut</strong>e–anOverview
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