ECE 492 Future Electronic Devices from Condensed Matter ...labsites.rochester.edu/swulab/wp-content/uploads/... · Spintronics Timeline 1990 2000 2010 Present Giant MR (GMR) Tunneling

ECE492FutureElectronicDevicesfromCondensedMatterPhysicsTopics

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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