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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Ohio(Neiman). Problemsfromcellbiophysicsareexploredincollaborationwithexperimentalgroups<br />
fromMunichandDresden. Specifically,weworkonintracellulardiffusionandtransport(Heinrich)and<br />
ontheproblemofcapturingofkinetochores(Tolić-Nørrelykke).Activemotilitymodelsarestudiedina<br />
jointprojectwitharesearchgroupinBerlin(Schimansky-Geier).<br />
Division:CondensedMatter<br />
(Head:Prof.Dr.R.Moessner)<br />
Incondensedmatterphysics,complexbehaviourarisesduetotheinteractionsbetweenalargenumberof<br />
microscopicdegreesoffreedom;thesefundamentaldegreesoffreedomcanthemselvesbeverysimple.<br />
Theresultingbehaviourisfascinatinginitsrichness: manydifferentphasesexistasdistinct‘vacua’,<br />
eachwithitsowncharacteristicpropertiessuchasground-statecorrelations,excitations,anddynamics<br />
inandoutofequilibrium. TheCondensedMatterdivisionstudiessuchcollectivebehaviour. Most<br />
fundamentally,theaimistoconnectthemacroscopicbehaviourofmatterwiththemicroscopicproperties<br />
ofitsconstituentparticles.Thisworkisnotonlyaimedatidentifyingandunderstandingnovelbehaviour,<br />
butalsoatidentifyingtheprinciplesaccordingtowhichwecanunderstandhowthephysicalworldis<br />
organised.<br />
Toachievethis,weutilisethemethodsofmany-bodyphysics,bothofanalytical(e.g.fieldtheories,<br />
exactsolutions),andnumerical(e.g.MonteCarlo,exactdiagonalisation)nature. Toguideandtest<br />
theory,abroadrangeofresultsfromexperimentalinvestigationsareavailable,whichthemselvesprofit<br />
fromthecombinatorialrichnesssuppliedbytheperiodictableofelements,andfromthepossibilityto<br />
custom-tailordegreesoffreedomandtheirinteractions. Progressoftennucleatesaroundexperimental<br />
breakthroughs,suchasthepossibilitytoinvestigatereal-timequantumdynamicsandwell-controlled<br />
time-dependentHamiltoniansinsystemsofcoldatoms,orverycleanelectronicsystemsprovidedby<br />
semiconductorheterostructuresandgraphene.<br />
Finally,theconceptsandmethodsofstatisticalmechanicshaveamuchwiderrangeofapplicabilitybeyond<br />
materials-basedmany-bodyphysics.Forinstance,theypermitustotakeabroaderviewofsubjectssuch<br />
asquantumcomplexitytheory,wheretheycanbeusedtoattackquestionsabouttypicalratherthan<br />
worstcasecomplexityincomputationalensembles.<br />
ResearchTopics<br />
Thesearchforemergentmagneticmonopoles: In2008,wepredictedthattheclassofmagneticmaterials<br />
whichgoesunderthenameofspiniceshouldexhibitelementaryexcitationsintheformofmagnetic<br />
monopoles.Subsequently,amulti-facetedexperimentaleffortgotunderwaywiththeaimoftestingthis<br />
prediction,asthiswouldinparticularconfirmspinicetobethefirstthree-dimensionalmagneticmaterial<br />
inwhichfractionalisationoccurs,inaphasedescribedbyaweaklyfluctuatingemergentgaugefield.<br />
WecollaboratedwithSantiagoGrigeraandAlanTennantwhoconductedasetofthermodynamicsand<br />
neutronscatteringexperiments. Inprovidingaparameter-free,quantitativeDebye-Hueckeltheoryfor<br />
themeasuredheatcapacity,wewereabletoestablishthattheinteractingmagneticmonopolescouldbe<br />
describedasaweaklyinteractingmagneticCoulombliquid.Inaddition,weanalysedthespincorrelations<br />
duetothe‘Dirac’stringsofflippedspinswhichrunbetweendifferentmonopoles. Inaseparatelineof<br />
work,weinvestigatedthephaseorderingkineticsuponapproachingtheCoulombphase,withparticular<br />
viewofgeneratingalargeout-of-equilibriumpopulationofmonopolesatlowtemperature. Also,we<br />
providedatheoreticframeworktoexplaintheirrationalchargeofthemagneticmonopoleswhichalso<br />
accountsforpreviouslyknowninstancesofirrationalchargeinonedimension.<br />
Disorderinspinliquids: Theinterplayofdisorderandinteractionspresentsoneofthemostfascinating<br />
andchallengingaspectsofcondensedmatterphysics. Inthecontextofspinsystemswithquenched<br />
disorder,thephysicsofspinglassesandinfiniterandomnessphasesarejusttwoinstancesofconceptually<br />
newphysicswhichhaveariseninthepast. Itisnaturaltoaskmoregenerallywhathappenswhen<br />
quencheddisorderisintroducedinamagneticsystemexhibitinganovelcorrelatedgroundstate.Indeed,<br />
besidesasearchfornewtypesofdisorder-inducedphases,thepropertiesofmanyquantumsystems<br />
canbeprobedsensitivelythroughthecontrolledintroductionofimpurities.Wehavestartedtoaddress<br />
thissetofquestionsinthecontextofKitaev’shoneycombmodel,oneofthefewanalyticallytractable<br />
instancesofagaplessquantumspinliquid.Wehavefoundthatimpuritiesnucleateamagneticmoment<br />
1.8. DepartmentsandResearchGroups 17
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