The newly discovered superconductor La(O,F)FeAs (Tc = 26 K) was investigated using the neutron scattering technique. No spin-density-wave (SDW) order was observed in the normal state nor in the superconducting state, both with and without an applied magnet

themeasuredS(Q,ω)≈χ (Q,ω)/πcanbecompareddirectlytothetheoreticalχ (Q,ω)inFig.4.Powderav-eragingwillenhancethemeasuredintensityatQlargerthan|QAFM|tosomeextent,however,thesharpreso-nancepeakwillbelittlea ected.

Wedidnotobservethestronglyenhancedsupercon-ductingresonancepeakinLaO0.87F0.13FeAsat1.6K.Theupperlimitforintensityofsucharesonancepeakis0.5(1)µ2theB/meVsrperFefromourdata(seethebluecurveinbottomframe).Ifthepredictedresonancepeakisasstrongasintheunconventionalsuperconduc-torCeCoIn5,～30µ2ofmagnitudestrongerB/meVsrperCo[36],beingtwoor-dersthanourmeasurementlimit,itwouldhavebeenobservedinourexperiments.Ontheotherhand,iftheintensityoftheresonancepeakinLa(O,F)FeAsissimilartothatinYBa2Cu3O6+x,～0.2µ2B/meVsrperCu[37],itwouldnotbeobservedinourmeasurements.Theoretically,thepeakintensityfortheresonanceinLa(O,F)FeAswiththeextendeds-wavepairingdependsonthechoiceofdampingfactorandcorrectionsbeyondtherandom-phase-approximation[27].Forthed-wavepairingalsodiscussedin[27],themod-estchangeinthespindynamicswouldbebeyondthesensitivityofthispolycrystallineexperiment.

Insummary,thespin-density-waveorderofLaOFeAsisdisplacedbysuperconductivityinLaO0.87F0.13FeAs.Thepeaksinthetheoreticalphonondensityofstatesat12and17meVareobservedinourphononmea-surements.Thetheoryofphononmediatedsupercon-ductivity,whichfailstoproducethehighTC≈26K,thusisbasedonreliablephononcalculation.Ourexperi-mentssetanupperlimitof0.5µ2B/meVsrperFefortheresonancepeakinthespinexcitationsattheantiferro-magneticwavevector.Unconventionalextendeds-wavesuperconductivitymediatedbyspin uctuationsiscon-strainedbythelimit.

WewouldliketothankD.J.SinghandM.-H.DuforprovidingtheoreticalPDOSdata.WorkatLANLissupportedbyU.S.DOE,atUSTCbytheNaturalScienceFoundationofChina,MinistryofScienceandTechnologyofChina(973ProjectNo:2006CB601001)andbyNationalBasicResearchProgramofChina(2006CB922005).TheDCSatNISTispartiallysup-portedbyNSFunderAgreementNo.DMR-0454672.

Electronicaddress:wbao@lanl.gov

[1]Y.Kamiharaetal.,J.Am.Chem.Soc.128,10012(2006).

[2]

T.Watanabeetal.,Inorg.Chem.46,7719(2007).

[3]Y.Kamiharaetal.,J.Am.Chem.Soc.130,3296(2008).[4]X.H.Chen,T.Wu,G.Wu,R.H.Liu,H.Chen,andD.F.Fang,arXiv:0803.3603.

[5]

G.F.Chen,Z.Li,D.Wu,G.Li,W.Z.Hu,J.Dong,P.Zheng,J.L.Luo,andN.L.Wang,arXiv:0803.3790.

4

[6]Z.A.Ren,J.Yang,W.Lu,W.Yi,X.L.Shen,Z.C.

Li,G.C.Che,X.L.Dong,L.L.Sun,F.Zhou,etal.,arXiv:0803.4234.

[7]Z.A.Ren,J.Yang,W.Lu,W.Yi,G.C.Che,X.L.

Dong,L.L.Sun,andZ.X.Zhao,arXiv:0803.4283.

[8]G.F.Chen,Z.Li,D.Wu,J.Dong,G.Li,W.Z.Hu,

P.Zheng,J.L.Luo,andN.L.Wang,arXiv:0803.4384.[9]P.Cheng,L.Fang,H.Yang,X.Zhu,G.Mu,H.Luo,

Z.Wang,andH.H.Wen,arXiv:0804.0835.

[10]Z.A.Ren,W.Lu,J.Yang,W.Yi,X.L.Shen,Z.C.

Li,G.C.Che,X.L.Dong,L.L.Sun,F.Zhou,etal.,arXiv:0804.2053.

[11]R.H.Liu,G.Wu,T.Wu,D.F.Fang,H.Chen,S.Y.

Li,K.Liu,Y.L.Xie,X.F.Wang,R.L.Yang,etal.,arXiv:0804.2105.

[12]J.Dong,H.J.Zhang,G.Xu,Z.Li,G.Li,W.Z.

Hu,D.Wu,G.F.Chen,X.Dai,J.L.Luo,etal.,arXiv:0803.3426.

[13]C.Cruz,Q.Huang,J.W.Lynn,J.Li,W.Ratcli ,J.L.

Zarestky,H.A.Mook,G.F.Chen,J.L.Luo,N.L.Wang,etal.,arXiv:0804.0795.

[14]M.A.McGuire,A.D.Christianson,A.S.Sefat,R.Jin,

E.A.Payzant,B.C.Sales,M.D.Lumsden,andD.Man-drus,arXiv:0804.0796.

[15]D.J.SinghandM.-H.Du,arXiv:0803.0429.

[16]H.H.Wenetal.,Europhys.Lett.82,17009(2008).[17]W.Lu,J.Yang,X.L.Dong,Z.A.Ren,G.C.Che,and

Z.X.Zhao,arXiv:0803.4266.

[18]B.Lorentz,K.Sasmal,R.P.Chaudhury,X.H.Chen,

R.H.Liu,T.Wu,andC.W.Chu,arXiv:0804.1582.[19]I.I.Mazin,D.J.Singh,M.D.Johannes,andM.H.Du,

arXiv:0803.2740.

[20]K.Haule,J.H.Shim,andG.Kotliar,arXiv:0803.1279.[21]L.Boeri,O.V.Dolgov,andA.A.Golubov,

arXiv:0803.2703.

[22]K.Kuroki,S.Onari,R.Arita,ui,Y.Tanaka,

H.Kontani,andH.Aoki,arXiv:0803.3325.

[23]X.Dai,Z.Fang,Y.Zhou,andF.Zhang,arXiv:0803.3982.[24]Q.Han,Y.Chen,andZ.D.Wang,arXiv:0803.4346.[25]H.Eschrig,arXiv:0804.0186.

[26]P.A.LeeandX.G.Wen,arXiv:0804.1739.

[27]M.M.KorshunovandI.Eremin,arXiv:0804.1793.

[28]G.F.Chen,Z.Li,G.Li,J.Zhou,D.Wu,J.Dong,

W.Z.Hu,P.Zheng,Z.J.Chen,J.L.Luo,etal.,arXiv:0803.0128.

[29]G.Mu,X.Zhu,L.Fang,L.Shan,C.Ren,andH.H.

Wen,arXiv:0803.0928.

[30]L.Shan,Y.Wang,X.Zhu,G.Mu,L.Fang,andH.H.

Wen,arXiv:0803.2405.

[31]H.Yang,X.Zhu,L.Fang,G.Mu,andH.H.Wen,

arXiv:0803.0623.

[32]X.Zhu,H.Yang,L.Fang,G.Mu,andH.H.Wen,

arXiv:0803.1288.

[33]rsonandR.B.VonDreele,GSAS:Generalized

StructureAnalysisSystem,(LosAlamosNationalLab-oratory,1994).

[34]T.Yildirim,arXiv:0804.2252.

[35]R.Osbornetal.,Phys.Rev.Lett.87,017005(2001).[36]C.Stocketal.,Phys.Rev.Lett.100,087001(2008).[37]S.M.Hayden,H.A.Mook,P.Dai,T.G.Perring,and

F.Doˇgan,Nature429,531(2004).