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

FIG.3:(coloronline)Top:I(ω)=R

dQS(Q,ω)measuredat1.6and110K.Theintegrationrangeisfrom2.5to7 A 1.Middle:Calculatedbareintensitypro leat1.6and110K.Bottom:MeasuredI(Q)=R

dωI(Q,ω)at1.6and110K.Theintegrationrangeisfrom-15to-5meV.Theshadedpro leismeasuredS(Q,ω=0).

toQ2I(Q,ω=

0)[35].ThepeakpositionsofthebarePDOSofSinghandDuarewellreproducedinthemea-suredI(ω).ThecalculatedPDOSin[21]closelyresem-blesthatin[15].Thus,thephononspectrausedintheelectron-phononcouplingcalculationsin[19,21],whichdonotfavorthephononmechanismforsuperconductiv-ityinLa(O,F)FeAs,haveexperimentalsupportfromthiswork.

Unconventionalsuperconductivitymediatedbyvariousmagneticchannelshasbeeninvestigatedtheoretically[19,22,23,24,25,26,27].Bothd-waveandextendeds-wavehavebeenproposedforthesuperconductingorderpa-rameterofLn(O,F)FeAs.KorshunovandEreminhaveinvestigatedtheconsequencesofthesepairingsinspindynamics[27].Ford-wavepairing,thesuperconductingtransitiononlymodestlyredistributesthespinspectralweightbelow2 0,where 0isthesuperconductinggap

3

FIG.4:(coloronline)Theoreticalχ (Q,ω)inthesuper-conductingstatewithanextendeds-waveorderparameter,from[27],isshownintheleftinsetinthebottomframe.Theχ (QAFM,ω)asafunctionofωinthenormalandsupercon-ductingstatewiththetwoorderparametersymmetries[27]areshowninthetop.MeasuredS(Q,ω)≡χ (Q,ω) n(T,ω)+1 /π≈χ (Q,ω)/πat1.6Kisshownintherightinsetinthebottomframe.Thecolorbarindicatesofµ2B/meVsrFe.TheI(ω)≈χ

intensityintheunits

(QAFM,ω)/πisshowninthebottomframe.

parameter.Forextendeds-wavepairing,astrongres-onancepeakwouldappearatthenestingwavevectorQAFM=(1/2,1/2,0)and ω～1.5 0.IntheleftinsetofthebottomframeandthetopframeofFig.4,thethe-oreticalimaginarydynamicspinsusceptibilityχ (Q,ω)from[27]isshownforvariouscases.Thevalueof 0ob-tainedfrominfraredmeasurementsisbetween3.1and3.7meV[28],inthespeci cheatstudy3.4(5)meV[29],andfromtunneling3.9(7)meV[30].Therefore,theresonancepeakatQAFMisbetween4.4and6.9meV.

Intherightinsettothebottomframeof gure4,mag-neticneutronscatteringintensityS(Q,ω)measuredinthesuperconductingstateat1.6Kisshowninthesame(ω,Q)rangeasintheleftinset.Below2.5meV,intensityisdominatedbyincoherentnuclearneutronscatteringandisnotshown.Theenergydependenceattheanti-ferromagneticpointisshowninthemainbottomframewiththesameenergyscaleasinthetopframe.Above2.5meV,theBosefactorn(ω,T)≈0at1.6K.Thus,