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ECE492FutureElectronicDevicesfromCondensedMatterPhysicsTopics
[email protected]:F9-10AMHPN340
http://labsites.rochester.edu/swulab/teaching/ece-492-course-materials/
Lecture7:Purespincurrents&topologicalspintronics
SpintronicsTimeline
1990
2000
2010
Present
GiantMR(GMR)
TunnelingMR(TMR)
MagneticTunnelJunctions(MTJ)
SpinTransferTorque(STT)Spininjection&diffusion
STTMagneticSwitching
SpinTorqueNano-oscillators
SpinHallEffect
SpinSeebeckEffectSpinOrbitTorques(SOT)
TopologicalSOT
SpinPumping
STT-MRAM
SOT-MRAM
SpinHallNano-oscillators
Magnonics
Pre-spintronics
SpintronicsTimeline
1990
2000
2010
Present
GiantMR(GMR)
TunnelingMR(TMR)
MagneticTunnelJunctions(MTJ)
SpinTransferTorque(STT)Spininjection&diffusion
STTMagneticSwitching
SpinTorqueNano-oscillators
SpinHallEffect
SpinSeebeckEffectSpinOrbitTorques(SOT)
TopologicalSOT
SpinPumping
STT-MRAM
SOT-MRAM
SpinHallNano-oscillators
Magnonics
Pre-spintronics
Spintronicswithoutcharge?
Ininsulatingsystems:
Magnon
Purespincurrent
X
Chargecurrent SpincurrentSpin-polarizedcurrent
Inconductingsystems:
----
Magnon spincurrents
RemoveI2RJouleheatingbyremovingcharge->neardissipationless spintransport
PurespinbasedelectronicsSpinHalleffect(SHE)
Transversespincurrentgeneratedforlongitudinalchargecurrentinconductors
JC
SpinHalleffect(SHE):Spincurrentgeneration
JS
InversespinHalleffect(ISHE):Spincurrentdetection
JS
JC
Magnons (Spinwaves)Quasiparticlecollectivemagneticexcitation
Mediatedthroughmagneticexchangeinteraction
MagnonicsUsingmagnons tocarryspininformation(typicallymagneticinsulators)
ThispictureusesSHEandISHEtogenerateanddetectmagnons butothermethodsexist
SpinCaloritronicsSpinSeebeckeffect(SSE)
--
-
-++
++
sT
ConventionalSeebeck Effect:ChargecurrentfromsT
sT
SpinSeebeck Effect:SpincurrentfromsT
LongitudinalSSE:K.Uchida,etal.,Appl.Phys.Lett. 97,172505 (2010)
SpinHallEffect&otherHallEffects
SpinHallEffectPredictionandDiscoveryPredictedin1971…
Signsofinversespinhalleffectdiscoveredin1986(Sov.Phys.JETPLett.44,59(1986))
Repredicted in1999
SpinHallEffectPredictionandDiscoveryExperimentalobservationofdirectspinHalleffectinlate2004 Kato(2004)
Wunderlich (2005)
Source:Kato(2004)
OpticallymeasuredspinHalleffectinducedspinaccumulation
SpinHallEffectExperimentsSoonfollowedall-electricSHEmeasurements
Source:Valenzuela(2006)
Injectspincurrent,detectusingISHE
MagnitudeofSHE&SpinorbitcouplingPhenomenologicallycharacterizespinHalleffectwithspinHallangle
Largevariationduetodifferentexperimentalmethods
Generallyscaleswithspin-orbitinteraction
LargerZmeanslarger𝐿 " 𝑆
SpinHallEffectMagneticSwitching
Source:Liu(2012)
WecanswitchmagnetizationinMTJ’susingspinHalleffect
SpinOrbitronicsMoreefficientgenerationofspincurrentthroughspin-orbittorques(SHE,..etc)
Source:Hoffmann
l/tcanbelargebydesign
OtherwaystogeneratespincurrentRashba effect Spinbandsplittingduetointerfaceinversionasymmetryand
spin-orbitcoupling
Ag
Bi
Rashba Interface
Rashba Effect
Source:Rojas-Sanchez(2013)
“InversespinHalllike”voltagefromRashba interface
InverseRashba-EdelsteinEffect
ControlofRashba effectwithEfield
Source:Lesne (2016)
TopologicalInsulatorsCanwedoevenbetterwithtopologicalinsulators?
Topologicalmaterialswinnerof2016NobelPrize
Topologyinbandstructure
“Same”ifcanbedeformedwithoutsingularity(pinch,poke,…)
TopologicalinvariantsSource:D.Vanderbilt
TopologyinbandstructureTopologicalinvariantsinelectronicbandstructure
ReplacegeometriccurvatureforBerrycurvatureinmaterialsSource:D.Vanderbilt
Topologyinbandstructure
Topologicalinvariantsexistinelectronicbandstructure
Edgestatesexistattheboundarywheretwotopologicallyinequivalentstatesmeet
Considered“topologicallyprotected”duetosymmetriesofmaterialSource:D.Vanderbilt,J.Moore
RelationtoQHEMagneticfieldinducedprotectededgestates
Canbeunderstoodasaboundarybetweentwotopologicallynonequivalentmaterials
Topologicalorder:DescribesmuchlargerclassofmaterialsthanjustQHE
QuantumHallEffectsReplacemagneticfieldwithspin-orbitcoupling:TwocopiesofQHE
QuantumspinHalleffector2Dtopologicalinsulator
Topologicalinvariant:Chern Parity
QuantumHallEffects
2DTI:PropertiesandExperiments
Source:PhysicsToday
TrivialInsulator TopologicalInsulatorHgTe QuantumWells
3DTI:PropertiesandExperiments
3Dsurfacestates
Graphene-likedirac stateswithspinmomentumlocking
Bi2Se3
TopologicalspincurrentsDirectlygenerateanddetectspincurrentbypassingcurrentthroughTI
Source:Li(2016)
TopologicalMagnetizationSwitching
Source:Fan(2014)ClaimspinHallangleof140-425
Purespincurrentsummary
• Newfieldofspin-orbitronics promiseMTJmagnetizationswitchingthatmaybemoreefficientthantraditionalSTT
• Currentlyexploringvariousmechanismstogeneratepurespincurrent&variouswaystocontrol
• Moretopologicalmaterialswithmoreuniquespintexturesarebeingdiscovered
Nexttime:Functionalcomplexoxides
