Electronic transport spectroscopy of carbon nanotubes in a magnetic field

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1、PHYSICALREVIEWLETTERSweekendingPRL94,156802(2005)22APRIL2005ElectronicTransportSpectroscopyofCarbonNanotubesinaMagneticFieldP.Jarillo-Herrero,J.Kong,*H.S.J.vanderZant,C.Dekker,L.P.Kouwenhoven,andS.DeFranceschiKavliInstituteofNanoscience,DelftUniversityofTechnology,P.O.Box5046,2600GADelft,TheNetherla

2、nds(Received30September2004;published22April2005)Wereportmagneticfieldspectroscopymeasurementsincarbonnanotubequantumdotsexhibitingfourfoldshellstructureintheenergylevelspectrum.Themagneticfieldinducesalargesplittingbetweenthetwoorbitalstatesofeachshell,demonstratingtheiroppositemagneticmomentanddeter

3、miningtransitionsinthespinandorbitalconfigurationofthequantumdotgroundstate.Weuseinelasticcotunnelingspectroscopytoaccuratelyresolvethespinandorbitalcontributionstothemagneticmoment.Asmallcouplingisfoundbetweenorbitalswithoppositemagneticmomentleadingtoanticrossingbehavioratzerofield.DOI:10.1103/PhysR

4、evLett.94.156802PACSnumbers:73.63.Fg,73.22.-f,73.23.HkTheremarkableelectronicbehaviorofcarbonnanotubesBothvalenceandconductionbandshavetwodegenerate(CNTs)originatesfromaparticularcombinationofthesubbands,labeledasand.AjikiandAndo[6]symmetrypropertiesofthegraphenebandstructureandpredictedthattheorb

5、italdegeneracyshouldbeliftedbyathequantizationofmomentumimposedbyperiodicmagneticfieldparalleltotheCNTaxis[Fig.1(a)].Thisboundaryconditionsalongthenanotubecircumferenceeffectcanbeunderstoodbynotingthat,duetoclockwise[1].Thissymmetryresultsinafourfolddegenerateshellandanticlockwisemotionaroundthetube,

6、electronsinstructureintheenergyspectrumofCNTquantumdotsdegenerateandsubbandsshouldhaveoppositeorbital(QDs).InearlyexperimentsonCNTQDs[2,3],however,magneticmoments,orb.InthecaseoffinitelengthCNTs,thissymmetrywasnotobserved,presumablyduetotheadiscreteenergyspectrumisexpectedfromsizequantiza-presence

7、ofdefects.ImprovementsinthequalityofCNTstion.ThelevelspectrumofaCNTQDcanthenbede-andadvancesinnanofabricationtechniqueshaveenabledscribedastwosetsofspindegeneratelevels,EnandEn,therecentobservat