Contents - Max-Planck-Institut für Physik komplexer Systeme

Externalcollaborations Icurrentlyworkwithseveralexternalgroups.Sofarthefollowingtwocooperationshaveleadtopublications:
• WithAndersKarlhedeandhisgroupatStockholmUniversity,IworkonfractionalquantumHall
effects. DuringmytimeonPKSwe,amongotherthings,foundanewsolvablelimitoftheFQH
system—onathickandshortcylinder—whichisverysimilartotheHaldane-Shastryspinchain.
• WithMasaakiNakamura,TokyoInstituteofTechnology,andJuhaSuorsa,OsloUniversity,we
haveworkedoutrelationsbetweenquantumspinchainsandfractionalquantumHallstates. In
particularwehaveinvestigatedtheconnectionbetweentheodddenominatorruleforFQHstates
andintegerversushalf-integerspinchains.
Articlescompletedandwrittenatthe mpipks
1. ”EffectivespinchainsforfractionalquantumHallstates”,E.J.Bergholtz,M.NakamuraandJ.Suorsa,PhysicaE
43,755(2011).
2. ”SymmetryBreakingontheThree-DimensionalHyperkagomeLatticeofNa4Ir3O8”,E.J.Bergholtz,A.M.Läuchli
andR.Moessner,Phys.Rev.Lett.105,237202(2010).
3. ”Entanglement Scaling of Fractional Quantum Hall states through Geometric Deformations”, A. Läuchli, E.J.
BergholtzandM.Haque,NewJ.Phys.12,075004(2010).
4. ”DisentanglingEntanglementSpectraofFractionalQuantumHallStatesonTorusGeometries”,A.M.Läuchli,E.J.
Bergholtz,J.SuorsaandM.Haque,Phys.Rev.Lett.104,156404(2010).
5. LinkbetweenthehierarchyoffractionalquantumHallstatesandHaldane’sconjectureforquantumspinchains,M.
Nakamura,E.J.BergholtzandJ.Suorsa,Phys.Rev.B81,165102(2010).
6. Spinchaindescriptionofrotatingbosonsatnu=1,E.Wikberg,E.J.BergholtzandA.Karlhede,J.Stat. Mech.
(2009)P07038.
7. QuantumHallCircle,E.J.BergholtzandA.Karlhede,J.Stat.Mech.(2009)P04015.
3.3.2 JuniorProfessorship
Unconventionalsuperconductivityandmagnetisminstronglycorrelatedelectronicsystems
(Prof.IlyaEremin)
Themicroscopicunderstandingofmany-particlephysicsincorrelatedmaterialswithunderlyinglattice
structureisattheheartofcurrentresearcheffortsinsolidstatephysics.Thisinterestraisedintheeighties
withthediscoveryofmaterialswith f-electrons,whichbehaveasheavyfermionsystemsandfurther
explodedwiththediscoveryofcuprateandrecentlyiron-basedsuperconductors. Manyunconventional
superconductorsarehighlycorrelatedandcomplexsystemswhosephasediagramsincludemagnetic,
superconducting,andchargeorderedphasesincloseproximity. Generally,Iaminterestedinstudying
bothanalyticallyandnumericallythepossiblemechanismsoftheunconventionalsuperconductivityand
theirfingerprintsandconsequencesforthespinandthechargedynamics. Furthermore, Iamalso
aimingtounderstanddeepertheaspectsoftheco-existenceandcompetitionbetweenunconventional
superconductivityandmagneticandchargeorderedphases.InApril2010IbecameAssociateProfessor
forSolidStateTheoryattheRuhr-UniversityinBochum. Thereportcoverstheperiodofmystayat
mpipkstillthisdate.
Projectsatthe mpipks TogetherwithJ.-P.Ismer(Ph. D.studentatthe mpipkswhoisdefending
histhesisinMayof2011)Iworkontheunderstandingofthecompetitionbetweendensitywavesand
unconventionalsuperconductivity. TogetherwithPeterFuldeandAlirezaAkbari,Ihavealsostudied
thepropertiesoftherare-earthimpuritiesinnovelsuperconductors.Forexample,wehaveanalyzedthe
boundstateinducedbythe4f-impurityinthecuprateandiron-basedsuperconductors.TogetherwithJun
ChangwehaveinvestigatedtheCooper-pairformationbyanharmonicrattlingmodesinthe β-pyrochlore
superconductorKOs2O6.IncollaborationwithJ.Knolle,andR.Moessnerwehavestudiedthespinwave
excitationswithinitinerantscenariointheparentmagneticphaseofiron-basedsuperconductors(seealso
contributiononpage94).Ourresultswereusedbytheneutronscatteringexperimentstoelucidatethe
natureofthespinexcitationinthesecompounds.
JuniorProfessorship 107