Gate Control of Spin Transport in Multilayer Graphene

By H. Goto et al.

Kun Xu

AdvantagesAdvantages of spin over charge:

◦Easily manipulatable with externally applied magnetic fields

◦Long coherence/relaxation time

GMR

Giant magnetoresistance◦Sandwich structure

FNF

◦Spin valve (HDD read/write heads)

◦The 2007 Nobel Prize in physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR

Disadvantages

Existing spin devices do not amplify signals

Datta-Das Device

Current modulated by the degrees of precession in electron spin introduced by the gate field

Spin-based quantum Computer

Qubit – intrinsic binary unitsQuantum entanglementSingle electron trapped in a

quantum dot

Spin transport in graphite based devicesCarbon nanotubesGrapheneMultilayer graphene (MLG)

Weak spin-orbit and hyperfine interaction

Gate control of spin conduction

Device StructureMLG Exfoliated from kish

graphite2.5nm thick, about 7 layers (by

SEM/AFM)Doped Si/SiO2 substrate

Device Structure50nm Co electrodes

200nm/330nmSeparated by L=290nm

Device StructureCr/Au nonmagnetic electrodes5nm/100nm thick

MeasurementFour terminal lock-in technique4.2KExcitation current of 1.0 uA,

119HzBack gate bias

Spin Signal: Rs

Rs=Rp-Rap

Proportional to Rwhen FN interfaces are

opaqueProportional to 1/R

when FN interfaces are transparent

Spin Signal: Rs

Spin Signal: Rs

Vn=1.5V

Spin relaxation length

Spin relaxation lengthMLG

Graphene: 1.5-2 um at room temperaure, may stay the same at low temperature

?