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ChargeorderedstateanditsstabilizationinorganiccompoundsF.Nad'.b,P.Monceaub・*,H.M.Yamamotoc'1nstitUιeojRodioeη宮ineeringondEledronics,RI、S,Mokh0Ⅷyα11/フ,125009MOSCOW,R山SioblnstitutN巨el,Dept.MCBI;CNRS・UIE25ruedesMar砂IS,BP166,38042Crenoblecedeχ9,Fronce'conde11SedMolecularMotehabιaboratoriesR1κEN,2-1Hirosawawoko.shi,saitoma351-0198,japan

ContentslistsavailableatscienceDirect

ARTIC工E

PhysicaB404(2009)4乃→75

journalhomepage:WWW.elsevier.com/10cate/physb

Keywords:

10W-dimensionalcompoundsStabili2ationofchargeorderedstateDielectricspectroscopyClass-1ikestate

INFO

PhysicaB

1.1n廿odⅡC廿on

Asknown,achargeordered(CO)stateisoneofapossiblegroundstateinquasi-one-dimensional(1D)andquasi-two-dimensional(2D)organiccompounds(seeReviewn-31andreferencestherein).1ΠShort,thesecompoundsconsistofthreebasicsubsystemsinteractingeachother:organicmolecu】esStackedinonedirection,chainsofanionsplacedbetweenmolecularchainsandelectrons.1nusualconditionstheelectrons

(holes)arehomogeneouslydistributedontheorganicmoleculesformingthesitesofthecfysta11attice.However,underce此ainCond辻ions(tempera加re,pressure,electronconcentration)theeleC廿onsubsystemcanobtainanenergy宮ainbyaredistribuuonOfchargesbetweenneighbormolecules^:hargedisproportiona-tion(CD)-whichcorrespondstoa4kFchargemodulauonalongthemolecularchains.i.e.acostate.suchachargesuperstrudureisoneformofW璃nercrystaⅡizationinamolecularlattice.Themaind"venforcefortheformauonofcDandcoisstrongelectron-electroninteractionsofcoulombtypeindudingnext-neighborinteractions.Therearemanytheories,mainlybasedontheextendedHubbardmodel,whichprovethepossibilityoftheformationofacostateinlDand2DorganiccompoundsHowever,thechangeintheelectronsubsystemandtheformationOfthecoupsetthepreviouslyexistingchargebalancealongaⅡthecrystaland.inresult,thetwoothersubsystemshavetorespondonthatchangebyappropriateshiftsordeformations.

ABSTRACT

WithlDand2Dorganiccompoundsasexamples,itisshownthatforstabilizationofthechargeoTderedStatetheappropriatereorganiza廿onofanionandmolecularsublatticesisnecessary.

@2008ElsevierB.V.Nlrightsreserved.

^凹^

Studiesshowthatatace此aintemperaturethehomogeneousdistributionofchargealongmolecularchainschangesbytheappearanceofcharge-richandcharge-poormolecules.TheformationofthecDwithdecreasingtemperaturewascon6rmedbyx-raydiffractionpa壮emscorrespondingtoa4kFchargedensitymodulauonofthewignerclystaltype.

Thestudiesofrealandimaginarypartsof血econdudanceinOtherquasi-1DorganiccompoundsofthedMTrF)2Xfamily(wherexareanionsofvariouschargesymmetry)showtheCharacteristicfeaturesindicatingasecond-orderphasetransiuonnearsometemperatureTcointoanewcogroundstate:sharpdecreaseoftheconductanceanddivergenceofthedielectricPermituvityε'inaccordancewiththecurielaW12,3.Theseresultswerecon6rmedbyNMRstudiesindMTrF)2XwhichshowthesplittingofNMRlinesatTくTΦCorrespondingtotheformauonofcDalongTMTrFchainS151.Atthesametime,X-raystudiesofthesecompoundsdonotbringanyindicationofChangesinthemolecularlatticeat加etransitionintothecostate,Whichwasca11ed"structurelesstransition"161.

However,inspiteoftheunitceⅡofthemolecularlatticeisnot

Changed,thespacesymmetryischangedasaresultofthelostoftheinversioncentre【2,3,フ.Forcompensationofsuchchanges,itWasproposed3.71thattheshi丘oftheanionchainsasa、Nhole

Withthewavevectorq=oturnsouttobethemostadvanta-geous.Thatleadstotheremovalofthechargesymmetrydisbalanceandtherestorationof血estabilityofthemolecularCfystal.Thus.thestabilizationofthecostateoccursbytheshiftoftheanionchainswithrespecttotheirinitialsymmetricalPosiuons.2.stabi"za廿onofcoinlDorganiccomp0Ⅱnds

The6rstexperimentalevidenceoftheformationofcoinlD

Compoundswasobtainedinthe(DI-DCNQI)2Agsalt【4.NMR

'correspondingヨUthor

E・mailaddress:pieπe.monceau@grenoble.cnrs.fr(P.Monceau)

0921-45261$-seefrontmatter02008ElsevierB.V.AⅡrightsreserved.doi:10.1016b.physb2008.".039

Theexperimentalevidenceoftheformationofcointhe2D

OrganiCΦmpoundθ一(BEDT・Trn2Rbzn(SCN)4(Rbznsa1りWas

3.S仏biliza廿onofcoin2Dorganiccompounds

474

Obtained6rstbyNMRstⅡdieS18].considerablechangesintheNMRlineshapeweref0ⅡndbelowTCO=20OKresultingfrom

ENadetal./physicaB404ι2009)4乃一475

temperature5

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destroyedonheatingaboveabout150K.S11Chaqualitativepicture{1U.1nthequenchedatfastVeri丘edbyx-Tay1S

diffuserodS工Alithql=G,k,}),observedpreviouslyState

T>TC。,becomewealくerbutstiⅡexistbel0工NTCO.Additiona11y,TくTΦanotherdiffuserodswithq2=(0,k,1)appear.Themodula廿onofq241Peisdisorderedintheinterlayerdirection.A丘erannealing,q2growsintothesateⅡitere負ectionsofc*/2.Thus,thetendencytotheformationofco,exhibitedbytheelectronsubsystembutnotsupportedbytheappropriatemodi負Cationsinthemolecularlattice,doesnotleadtothe

formationofastablecostate己tthefastcooling.

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111H.seo,」.phys.SOC.japan69(200の805.【21F.Nad,P.Monceau,J.phys.SOC.Japan75(2006)051005.BIRMonceau,].C.1asjaunias.K.Biljakovic,F.Nad.Thephysicsofor宮anjc

Supefconductorsandconductors.in:A.Lebed(Ed.),springerseriesinMヨterialsdences,V01.110.2008.P.27フ

[4】K.Hilaki,K.Kanodヨ,phys.Rev.Le廿.80(1998)4737[51DS.chow,etヨ1,phys.Rev.Lett.85(2000)1698.[61」.P.P011get,S.Ravy,」.phys.1(pa"S)6(1996)1501;

].P.pouget,S.Raw,synth.Met.85(1997)1523[71J.RieTa.D.poilblanc,phys.Rev.B62(200の16243;

」.RieTa,D.poilblanc,phys.Rev.B63(2001)241102[81K.Miyagawa,A.Kawamoto.KKanoda,phys.Rev.B62(200のR7679[91K.Yamamoto.etal.,phys.Rev.B65(2002)08511011のENad,P.MonceヨⅡ,H.M.Yヨmamoto,」.phys.condens.Matter18(2006)L509[111M.watanabe.etal.,synth.Met.135-136(2003)665.[121YTanaka,K.YonemitSⅡ.」.phys.SOC.jaP且n76(2007)053708.[131ENad.P.Monceau.H.M.Yamamoto.phys.Rev.B76(2007)205101.1141P.Monceau.ENad,H.M.Yamamoto.]ournalofphysics:conferencesefieS13ユ

(2008)012008.

1151H.Tajima,etal..phys.Rev.B62(200の93781161Y.Nogami.etal..synth.Met.103a999)1911[1刀M.waねΠabe,et且1.,」.phys.SOC.japan68(1999)2654;

M.W且仏nabe.etal.,」.phys.1V.France12(2002)pr9-231.[181B.Lshklovskij.A.LE「ros.SOV.phys.」訂P54a981)218【1田K.Kanoda,etal.,J.phys.1VFrance131(2005)21.

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゛"'10""叩.....10叩......'巨匪叩。

Hg.3.Temperaturedependences Ofε'forcszn

indicatedne且rthecul、1esinMHZ

0

CompoundwhichissimilartotheRbznsalt(seeRef.1141andreferencestherein).1nfraredreflectanceandRamanspectrashow

thatnoopticalgapisobselvedinthecsznsaltinaⅡthe

temperaturerangedownt010K1151.NMRstudiesshowthat,asinthecaseofRbznsaltatT>TCO,alinebroadeningisobservedinCsznsaltbelo、んlabout180Kvvhichisassodatedwiththe

developmentofapartialcD.X-raystudiesshowthatincsznSalt,aswe11asinisostruduralcsc0116,171,intherange300-120Kstrongdiffusesheetsareobservedalong2a*十C*and

2a*-C、directions.BelovV90K2Ddiffuserodscorrespondingto

ql=(号,k,})andq2=(0,k,})developfromthedi仟Usesheets.withfurthercoolingthepeakintensityofq2increaseswhiletheqlChar宮emodulauonisalsoretained.Theconelationlengthsofql

andqユranges(domains)arenotverylarge(50-70A)f161.WeundertookmeasurementsoftheconductanceGandthe

dielectricpermittivityε'ofcsznsaltinordertoeluddatethemainfeaturesofitslowtemperaturestate1141.Thetemperature

dependenceofGshowsamaximumnear110Kwithaf0ⅡOwingbenddownW虻hasnねⅡthermalhysteresis.TheArrheniusplotof

Gbelowthemaximumisnotlinearinthetemperaturerange100-42K(Fig.2).1tmeans,probably,thatnorealenergygap

developsincsznsalt.althoughtheaverage"energygap"isConsiderablysma11erthaninRbznsalt.AnappredabledecreaseofCisobservedatT《20K.1ntherange43-20KthemostacCⅡrate

6tofthedependenceoftheacconductancecorrespondstotherelationc~Tn工Alithn=29.Thisvalueofnisverydosetothecase

Ofthehoppingconductivi目Iwithdisorder,ねkingintoaccount

alsotheelectroncorrelationeffectsforwhichc~T31181.Thetemperaturedependenceofε'areshowninFig.3.The

magnitudeofε'beginstogro、Nfromroomtemperature.Below10OKε'(乃dependencesshowmaximaatsometemperature

depende址on丘equencyf.withdecreasingf,thismaximumshiftst010wertemperatⅡres.simⅡltaneously,themaximummagnitude

Ofε'increases.suchformsofε'(T,Ddependencesareverysimilartotheknownslowingdownbehavior、Nhichischaraderisticfor

glasses.

50

Thus,asitf0ⅡOwsfromtheabovementionedresults,vlith

deceasingtemperaturethecsznsaltdoesnotachievethestable3Dcostatebutturnsintoaglass-1ikecostate[14.19].AtlowTtheexistenceoftw0司IpesofdomainslAlithdifferentstrudures,

Competingtoeachother,1eadstothedevelopmentoffrustration,i.e.whenincompatibleandcompetingtwofold(q2)andthreefold

(ql)statescorrespondtotwodegeneratefreeenergyminimawithVerydosevaluesintheirener別.Asaresultofsuch丑frustration

Someglassy-1ikecostatedevelops;itcorrespondstofreezesomedegreeofdisorderonthelong-rangescalebutwithconservationOftheshort-ran宮eordervvithasmaⅡCoherencelength11田.

100150 200

TempeぱUre(K)

differentfreq11enciesSヨ1t丑t

250 300

4.condⅡSion

ForthestabilizationofacostateinlDand2Dorganic

Compounds,owingtoelectron-electroncorrelatedinteractions,Certainmodincationsareneededinanionandlatticesubsystems.InlDFabresaltsthatistheshiftofanionchainsasa、Nholewith

q=0.1n2Dcomp0Ⅱnds,suchaSθ一(BEDT-1TF)2Rbzn(SCN)4,theStabilizationisrealizedbythedevelopmentofasuperstrudure

Withdoublingofthelatticeperiod.1fvvithdecreasingtemperaturethisdimerizationisnotrealizedonalong-rangescalebut,instead

Ofthat,aconglomerateofmanydomainswithdifferentstruduresturnsouttobefrozen,aglass-1ikecostateisdeve】oped,as

Observedinθ一(BEDT-1丁F)2Cszn(SCN)4.

475

References

Acknowled容ments

ThisworlくWassupportedbyRFBR(crant06-02-72551)intheframeofcNRS-RASAssociatedEuropeanLaboratory,andpartlyby

INTAS(Grant05-1000008-7972)andRFBR(Grant08-02-01093a).SupportoftheANRGrantBLAN07-03_192276isalsoacknowl-

edged.

【。