Gate control of spin transport in multilayer graphene
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Gate Control of Spin Transport in Multilayer Graphene. By H . Goto et al. Kun Xu. Advantages. Advantages of spin over charge: Easily manipulatable with externally applied magnetic fields Long coherence/relaxation time. GMR. Giant magnetoresistance Sandwich structure FNF

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Gate control of spin transport in multilayer graphene

Gate Control of Spin Transport in Multilayer Graphene

By H. Goto et al.

Kun Xu


Advantages
Advantages

  • Advantages 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
Disadvantages

  • Existing spin devices do not amplify signals


Datta das device
Datta-Das Device

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


Spin based quantum computer
Spin-based quantum Computer

  • Qubit – intrinsic binary units

  • Quantum entanglement

  • Single electron trapped in a quantum dot


Spin transport in graphite based devices
Spin transport in graphite based devices

  • Carbon nanotubes

  • Graphene

  • Multilayer graphene (MLG)

  • Weak spin-orbit and hyperfine interaction

  • Gate control of spin conduction


Device structure
Device Structure

  • MLG Exfoliated from kish graphite

  • 2.5nm thick, about 7 layers (by SEM/AFM)

  • Doped Si/SiO2 substrate


Device structure1
Device Structure

  • 50nm Co electrodes 200nm/330nm

  • Separated by L=290nm


Device structure2
Device Structure

  • Cr/Au nonmagnetic electrodes

  • 5nm/100nm thick


Measurement
Measurement

  • Four terminal lock-in technique

  • 4.2K

  • Excitation current of 1.0 uA, 119Hz

  • Back gate bias


Spin signal r s
Spin Signal: Rs

  • Rs=Rp-Rap

  • Proportional to R

    when FN interfaces are opaque

  • Proportional to 1/R

    when FN interfaces are transparent



Spin signal r s2
Spin Signal: Rs

Vn=1.5V



Spin relaxation length1
Spin relaxation length

  • MLG

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


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