Electrical initialization and manipulation of electron spins

An L-shaped strained n-InGaAs channel is used to polarize and subsequently rotate electron spins solely by means of electric fields. Precession of electrically-excited spins in the absence of applied magnetic fields is directly observed by Kerr rotation mi

Electricalinitializationandmanipulationofelectronspins

inanL-shapedstrainedn-InGaAschannel

Y.K.Kato,R.C.Myers,A.C.Gossard,andD.D.Awschalom

CenterforSpintronicsandQuantumComputation,UniversityofCalifornia,SantaBarbara,CA93106

(Dated:February2,2008)

AnL-shapedstrainedn-InGaAschannelisusedtopolarizeandsubsequentlyrotateelectronspinssolelybymeansofelectric elds.Precessionofelectrically-excitedspinsintheabsenceofappliedmagnetic eldsisdirectlyobservedbyKerrrotationmicroscopy.Inaddition,in-planeandout-of-planecomponentsofthespinpolarizationinthechannelaresimultaneouslyimaged.

eb 2005

F 6PACSnumbers:85.75.-d,72.25.Dc,72.25.Pn,71.70.Fk

2 ]Spin-orbite ectso erauniquedirectionforthede-llavelopmentof1,2,3byallowingspin-dependenthinteractionsthatrequireneithermagnetic eldsnormag--neticmaterials.Anumberofproposalstakeadvantageofsethespin-orbitinteractioninsemiconductorstoconstructmspintronicdevicesfromnonmagneticmaterials,4,5,6,7,8andrecentexperimentshavedemonstratedvariousman-.taifestationsofthespin-orbitinteractioninsemiconduc-mtorsystems.Ithasbeenshownthatane ectivein-ternalmagnetic eldBint,whichisproportionaltothe-ddriftvelocityofelectrons,existsinstrainedn-typeGaAsnandInGaAs,enablingcoherentmanipulationofelec-otronspinswithoutmagnetic elds.9Current-inducedcspinpolarization[13(CISP)10,11,12hasbeendetectedin thesesystemsandinatwo-dimensional 114holegasataGaAs/AlGaAsdemonstratingthefea-vsibilityofall-electricalspininitialization.ThespinHall715,16isanotherphenomenonoriginatingfromthe2spin-orbitinteractionandhasbeenobservedinn-type62unstrainedGaAsandstrainedInGaAs,17aswellasina0two-dimensionalholegas.18

50HereweshowthatitispossibletocombineCISPandB/intinstrainedsemiconductorstopolarizeandsubse-taquentlyrotateelectronspinsusingelectric eldsalone,mwithoutanappliedmagnetic eld.AKerrmicroscope-imagesthesteady-statespinpolarizationinanL-shapeddchannelofstrainedInGaAsinwhichthespinsorientinnonearmandprecessintheotherarm.

coSamplesarefabricatedfromawafergrownbymolec-:vularbeamepitaxyonasemi-insulating(001)GaAssub-istrate(wafer“E”asdescribedinpreviousworks9,13,17),Xwhichconsistsof500-nmthickn-In0.07Ga0.93As(Si-rdopedforn=3×1016cm 3toachievelongspina19,20)cappedwith100nmofundopedGaAs.TheInGaAslayershowsanisotropicstrain21butresidualstrainispresentasdeterminedbyX-raydi ractionatroomtemperature.Standardphotolithog-raphyisemployedtode neanL-shapedInGaAschannelconsistingoftwoarms,eachwithawidthof18µmandalengthof200µm,connectingatarightangle[Fig.1(a)].Thetop0.7µmofthesampleischemicallyetchedtoformthemesa,andthetwoendsoftheL-shapedchan-nelarecontactedbyannealingthefollowingmetallayers,

Au/Ni/Au/Ge/Ni,listedinorderfromthesurfacetothesubstrate.

Weconsiderthecasewhereanelectric eldisappliedsuchthattheelectrons owfromthehorizontalarmtotheverticalarmasshowninFig.Astheelectrons owtothe x-directioninthehorizontalarm,theirspinsarepolarizedinthe+y-directionbecauseofCISP.Aftertheelectronsmaketherightangleturnandstart owinginthe y-directiondowntheverticalarm,theelectronspinswillnowseeBintinthe+x-directionandstarttoprecess.Thiswillresultinanon-zerocomponentofspinpolarizationinthez-direction,allowingdetectionbyKerrrotationevenatzeroexternalmagnetic elds.Previousmeasurements9,13onasamplefromthesamewaferhaveshownanisotropyofCISPandBintforelectric eldEappliedalongthetwocrystalaxes[110]¯and[1¯10].LargerCISPhasbeenobservedwhenE [110],whileBintisP1throughP4arealsoindicated.The(x,y)coordinatesinunitsofµmareasfollows:P1(0, 5),P2(0, 15),P3(0, 25),P4(0, 35).(b)Voltage-inducedKerrrotationasafunctionofBextforthefourpositionswithE=15mVµm 1.Thecurvesareverticallyo setforclarity.

An L-shaped strained n-InGaAs channel is used to polarize and subsequently rotate electron spins solely by means of electric fields. Precession of electrically-excited spins in the absence of applied magnetic fields is directly observed by Kerr rotation mi

armalongthex-axisandthe[110]axisfortheverticalarmalongthey-axis.

Steady-statespinpolarizationisprobedbyalow-temperaturescanningKerrmicroscopeintheVoigtgeometry.17,22Thesampleisplacedinahelium owcryo-stat,andmeasurementsareperformedatatemperatureT=30K.Amode-lockedTi:sapphirelaseristunedtoawavelengthof873nm,andalinearlypolarizedbeamwithanaveragepowerof130µWisdirectedalongthez-axis(samplegrowthdirection)andfocusedthroughanobjec-tivelenswithanumericalapertureof0.73andaworkingdistanceof4.7mm.Thepolarizationaxisofthere ectedbeamrotatesbyanamountproportionaltothecompo-nentofnetspinpolarizationalongtheopticalaxis(Kerrrotation).AsquarewavevoltagewithafrequencyfE=1.169kHzisappliedtothetwocontactsandestablishesanalternatingelectric eldwithanaverageamplitudeE.Kerrrotationisdetectedbyabalancedphotodiodebridgeusingastandardlock-intechnique.Wenotethatthismeasurementschemealsodetectssignal

arisingfromelectron owoppositetothatdrawninFig.1(a),sincethechangeintheKerrrotationbetweenpositiveandneg-ativeelectric eldsismeasured.

InFig.1(b),Kerrrotationmeasurementsforscansoftheexternalmagnetic eldBextappliedparalleltothex-axiswithE=15mVµm 1isshownforvariousposi-tionsonthesample.Althoughthecurvesshowcomplexbehavior,qualitativeexplanationispossiblewithasim-plemodel.Westartbyconsideringthesteady-statespinpolarizationprepared13inthehorizontalchannel.Aswasdoneinpreviouswork,CISPismodeledasacontinuousorientationofspinsalongthey-axis.Thez-componentofthesteady-statespinpolarizationvectorS(x,y)justpriortotheright-angleturnis

Sz(0,0)= ∞dt γe t/τ

sin(ωLt) =

S0ωLτ0

(ωLτ)2

+1

,(2)

whichisequivalenttotheHanlecurve.23

Next,weconsiderthee ectofBint.Ifwepickapar-ticul …… 此处隐藏：11668字，全部文档内容请下载后查看。喜欢就下载吧 ……